ap chemistry lab manual and syllabus for students elegante

Avoid contact with acetic acid and readily oxidized substances.0.5M KSCN Slightly toxic by ingestion.. MSDS: 0.1 M FeNO33 Corrosive to body tissues by contact and inhalation.. Sodium Hig

7/24/2024 Page 1 of 116

AP Chemistry Lab Manual

Lab Notebook Guidelines 2

QRS lab 5

Qualitative Analysis of the Group III Cations 6

How Much Zinc is in a penny? 11

Predicting Products of Chemical Reactions 12

Redox Titration: The Standardization of Potassium Permanganate 13

The EMF Activity Series 15

Heat of Fusion for Ice 19

Additivity of Heats of Reaction: Hess’s Law 21

Heat of Combustion of a metal-an inquiry based approach 23

VSEPR and Molecular Geometry 25

Formation of a Coordination Complex of Copper (II) 26

Kinetics of a Reaction An Iodine Clock 28

Where did the Crystal Violet go? 30

Chemical Equilibrium: Finding a Constant, Keq or Kc 35

Entropy of a Reaction 37

Catalytic Converter—Hot Copper Catalysis 38

Equilibrium and Le Châtelier's Principle 40

Strong Acid Strong Base Titration 43

Titration of a weak acid 45

Determination of the Ka of Weak Acids 46

Determination of the Ksp of an Ionic Compound 49

Buffer Laptop Palooza 51

Preparation and Properties of Buffer Solutions 53

Corrosion Cells 56

Polyatomic Ions 59

Molecular Geometry 60

Rules of Writing Equations 62

AP Chemistry Syllabus 64

Class Rules 66

Description of Content Covered 67

End of Year Review 70

Solution Practice 79

Redox Practice 80

Thermochemistry: Standard Heats of Formation Worksheet 82

Gas laws practice 83

8 and 9 Practice worksheet 85

Equilibrium and Entropy Practice 89

Ch 10 questions 92

Chapter 11 Practice 92

Kinetics part I 94

Kinetics part II 97

Accessing Prior Knowledge Acids and Bases 100

pH PRACTICE 101

Ka and Kb practice 102

Titration Curve Practice 103

Chapter 14 and 15 practice: 110

Ksp practice Keep me but put all answers in your notes 112

Electrochem practice 114

7/24/2024 Page 3 of 116

Lab Notebook Guidelines

You must have a composition notebook or the notebook from Chem I as a lab notebook

A lab notebook should be used to explain lab procedures, record all lab data, and show how calculations are made You may also use the notebook to discuss the results of an

experiment and to explain the theories involved

A record of lab work is an important document which will show the quality of the lab work that you have done You may need to show your notebook and your lab reports to the Chemistry Department at a college or university in order to obtain credit for the lab part of an

AP Chemistry class As you record information in your notebook, keep in mind that

someone who is unfamiliar with your work may be using this notebook to evaluate your lab experience in chemistry When you explain your work, list your data, calculate values and answer questions, be sure that the meaning will be obvious to anyone who reads your

notebook

Guidelines for the notebook:

1 Write your name and class on the front cover

2 In black or blue ink, number all the right hand pages on the lower right corner if they are not already numbered

3 Save the first 2 pages for a Table of Contents This should be kept current as you

proceed Each time you write up a lab, place the title and page numbers where the lab report begins in the Table of Contents

4 Write in ink Use only the right hand pages

5 If you make a mistake, DO NOT ERASE OR SCRIBBLE Just draw ONE LINE throughyour error, and continue It is expected that some errors will occur A lab notebook is a working document, not a perfect, error-free, polished product Errors should be corrected

by drawing one line through the mistake, and then proceeding with the new data

6 Do not use the first person or include personal comments

Prelab Instructions:

1 On most every lab you will have prelab instructions If it has you read, read carefully

as there will often times be a quiz over that content If there are questions you are supposed to answer, do them on a separate sheet of paper and hand them in as your ticket into lab If there is a code word in the procedure or weird instructions be prepared to follow them

2 Some labs will be full write-ups and some will be data and calculations only You must always answer questions if they are in the lab manual You must get your data stamped in your lab notebook before you leave the lab

Lab Reports (Lab reports will be worth 50 points)

Include the following information in your lab reports Label each section

1 Title – The title should be descriptive Experiment 5 is not a descriptive title

2 Date and lab station – This is the date you performed the experiment and lab station

3 Purpose – A brief statement of what you are attempting to do Must be a sentence

4 Procedure – A shortened description of the method you are using You may refer to the lab manual for specific instructions, but you should include a brief statement of the method Do not include lengthy, detailed directions A person who understands chemistry should be able to read this section and know what you are doing

5 Reactions: Write a balanced reaction including states of matter for any reactions If there are no reactions omit this section

Organize your data in a neat, orderly form Label all data very clearly Use correct sig figs and always include proper units Underline, use capital letters or use any device you choose to help organize this section well Space things out – don’t try to cram everything on one page A data table must have a label and a title e.g – Table 1: Density Values for Sugar Solutions.

7 Calculations and Graphs- You should show how calculations are carried out Give the equation used and show how your values are substituted into it Give the

calculated values If graphs are included, make the graphs an appropriate size Label all axes and give each graph a title If experiments are not quantitative, this section may be omitted

8 Conclusions – Make a simple statement concerning what you conclude from the experiment This is not a place to give your opinion of the lab and whether or not it was “fun” It is not your job to review the lab like you would if you saw a movie

9 Experimental error – If there is a known value for something you are doing in lab, calculate the experimental error

10 Error Analysis – What are some specific sources of error, and how do they influence the data? Do they make the values obtained larger or smaller than they should be? Which measurement was the least precise? Instrumental error and human error exist

in all experiments, and should not be mentioned as a source of error unless they cause

a significant fault Significant digits and mistakes in calculations are NOT a valid source of error In writing this section it is sometimes helpful to ask yourself what you would do differently if you were to repeat the experiment and wanted to obtain better precision

11 Questions – Answer any questions included in the lab directions Answer in such a way that the meaning of the question is obvious from your answer

Reporting Lab Data Graphing Data

1 All graphs should have a descriptive title (“Graph” is not a title) and a label e.g – Graph A: Density of Solutions with Varying Sugar Concentrations

2 Both the vertical and horizontal axes should both have labels and units clearly

marked Use a ruler to draw the axes

3 The scales chosen should reflect the precision of the measurements For example, if temperature is known to be ±0.1ºC, you should be able to plot the value this closely Don’t have each block of the graph equal to 10ºC

4 There should be a table in which the data values are listed Don’t put data in a graph unless you have first listed it in a table

5 The controlled or independent variable is placed on the horizontal axis The

dependent variable is graphed on the vertical axis

6 There should be an obvious small point on the graph for each experimental value It

is not necessary to include the coordinates of each point since they will be in the data table

7 A smooth line should be drawn that lies as close as possible to most of the points DoNOT draw a line connecting one point to the next as in a dot-to-dot drawing If the line is a straight line, use a ruler to draw it

8 If a computer program is used to draw the graph, the rules still apply

Accuracy

Accuracy is a measure of how close an experimental value is to a value which is accepted as correct The measure of the accuracy of an experimental value is reported as Percent Error

7/24/2024 Page 5 of 116

Accepted

Accepted al

QRS lab

Reactions and explanations only, no full writeup

In this lab, there are three flasks labeled Q, R, and S Each flask contains one of the followingsolutions: 0.1 M Pb(NO3)2, 0.1 M NaCl, or 0.10 M K2CO3 Two other flasks are labeled X and Y One of these flasks contains 0.1 M AgNO3 and the other contains 0.1 M BaCl2

Mix each of the solutions with each of the other and record all observations For all

precipitates which form, you must write a balanced equation and net ionic equation and identify the precipitate You will need to wait until you have identified the solutions to write the equations As you carry out the reactions you must use as little solution as possible Part

of your grade is the way in which you are observed performing the reactions Frugality is key You must explain how you reasoned out the solution’s identity

7/24/2024 Page 7 of 116

Qualitative Analysis of the Group III Cations

No writeup Only data sheet

Cr3+ (aq) + 3OH-(aq) Cr(OH)3(s)

Al3+(aq) + 3OH-(aq)  Al(OH)3(s)

Fe3+(aq) + 3OH-(aq)  Fe(OH)3(s)

Mn2+(aq) + 2OH-(aq)  Mn(OH)2(s)

The pH is then raised with NaOH and hydrogen peroxide is added to further oxidize the precipitates The Fe(OH)3 (s) remains the same, the Mn(OH)2(s) becomes MnO2(s), the Cr(OH)3(s) oxidizes to the chromate ion CrO42-(aq) and the Al(OH)3(s) complexes with more hydroxide ion to form Al(OH)4-(aq)

6M NaOH Moderately toxic by ingestion and skin absorption Corrosive to body

tissues Causes severe eye burns Avoid all body tissue contact

3% H2O2 Slightly toxic by ingestion or inhalation Irritant to skin, eyes and

respiratory tract Avoid prolong body contact Hydrogen peroxide will decompose rapidly when exposed to almost any substance

3M H2SO4 Moderately toxic by ingestion Corrosive to eye, skin, and all other body

tissues Avoid all body tissue contact Very considerable heat generated when diluted with water

6M HNO3 Corrosive; will cause severe damage to eyes, skin and mucous

membranes Moderately toxic by ingestion and inhalation Strong oxidizer Avoid contact with acetic acid and readily oxidized substances.0.5M KSCN Slightly toxic by ingestion Irritating to body tissues Avoid all body

tissue contact Contact with acids or heat may liberate poisonous hydrogen cyanide gas

PbO2 Moderately toxic by ingestion or inhalation Irritating to body tissues

Avoid all body contact Oxidizer Lead and lead compounds are possible carcinogens

6M HC2H3O2 Substance not considered hazardous However, not all health aspects of

this substance have been thoroughly investigated

0.1 M

Pb(C2H3O2)2

Moderately toxic by ingestion and skin absorption Eye and skin irritant Possible carcinogen Avoid ingestion, inhalation and skin absorption Chronic exposure to inorganic lead via inhalation or ingestion can result

Procedure

Obtain a Group III known sample which contains all of the ions You will get a Group III unknown solution (which may contain any or all of these cations) after you have completed the known All glassware should be cleaned, rinsed and rinsed with distilled water before starting the lab

1 Place 1-2 mL of solution to be tested in a small test tube

2 Add 1 mL of 2 M ammonium chloride solution to the

sample in the test tube and stir Add 6 M aqueous ammonia to

the sample dropwise until the solution is just barely basic

(remove a drop of the solution with a stirring rod and touch

the drop to a strip of pH test paper)

3 Add about 3 mL of distilled water to wash the precipitate

Mix thoroughly, centrifuge, decant and discard water

4 Add ~ 2mL 6M NaOH to the residue and mix

5 Add 10 drops 3% H2O2 and mix immediately Boil

several minutes to remove excess H2O2 If solution is green,

add more H2O2 (yellow is okay) Look for separation of

precipitate and supernatant Centrifuge, decant and obtain

residue 2 for step 6, and decantate 2 for step 12 Do not

discard If necessary, recentrifuge decantate 2 until

absolutely clear or filter into another test tube.

6 Add 1-2 mL 3M H2SO4 to residue 2 Mix

7 Add 5-6 drops 3%H2O2 to hasten the process Mix

thoroughly If it doesn’t dissolve, heat for a few minutes until

all the solid dissolves

8 Dilute solution to a total of 4 mL with distilled water and

divide the solution into 2 parts to be tested for Fe3+ ions in

step 9 and Mn2+ ions in step 10

9 Add 1-2 drops 0.5M KSCN to one test tube from part 6

A blood red solution indicates the presence of Fe3+ ions

10 To the other half of the solution from step 6, add ~ 1mL

6M HNO3 and mix

11 Add solid PbO2 equivalent to 1/10 the volume of the

liquid Mix well and Boil for 2-3 minutes and let stand for 3

minutes If Mn2+ ions are present, the solution will turn a

pink to dark purple color If test is negative, add another

small portion of acid, mix and Boil solution Centrifuge

12 Dilute decantate 2 from step 4 to ~ 4mL with distilled

water and divide into two parts to be tested for Al3+ in step 13

and CrO42- in step 14

13 Add ~ 2mL 2M NH4Cl to the first half of decantate from

step 12 DO NOT MIX Place in Boiling water for 5

minutes Look closely for a fluffy, translucent solid in the top

layer which indicates the presence of Al3+ ions If uncertain

about the aluminum test, centrifuge If other ions are present,

7/24/2024 Page 9 of 116the decantate may not be clear and a halo effect may be seen

around the precipitate The iron and manganese hydroxides

will spin down first because of the greater densities and the

aluminum hydroxide will be on top

14 Add 6M HC2H3O2 to second half of decantate from step 9

until acidic to litmus paper Add 1-2 drops 0.1 M

Pb(C2H3O2)2 Let stand for 3 minutes A white or yellow

precipitate is a positive test for CrO42- ions

Presence of Manganese ion Yes No

MnO

4 -

PbCrO

4

yellow or white

Group III Cation Analysis

7/24/2024 Page 11 of 116

How Much Zinc is in a penny?

Full writeup

Discussion

Up until 1982 pennies were made with mostly copper The history of the penny shows a plethora of changes in composition and sizes but I digress If you are interested, google it In an effort to save money the treasury started putting a zinc core with a thin copper skin around it In this lab you will scratch away the thin copper on an edge to expose the zinc You’ll then soak it in acid overnight to dissolve the zinc You will then choose a salt that you can use to precipitate out the zinc and calculate the mass of zinc in a penny

Procedure

Write your own Pick an acid, 6 M HCl, 6M H2SO4, or 6M HC2H3O2

Write out a procedure to dissolve the zinc and then choose a salt from the storeroom that you can dissolve in water and add to the dissolved zinc to precipitate it out

You must get your procedure approved by your teacher

Collect your data and look up the actual value online Cite your source when you report the expected mass of the zinc Calculate a percent error

Questions:

1 Why not use iron? Iron’s cheap

2 Name 2 other salts that you could have used to precipitate out the zinc

7/24/2024 Page 13 of 116

Predicting Products of Chemical Reactions

Only reactions and data

compounds Even though a weak acid such as acetic acid does ionize slightly in water, the percent of ionization is very small Only the formulas of the major species are shown in the net ionic equation Solids, gases, and nonionic liquids, whether dissolved or nor, are written

as neutral, molecular formulas See your notes about types of reactions

Procedure:

Carry out the reactions as described Create a data table in which you describe the reactants, products, and any indication that a reaction has occurred Identify the type of reaction Write a net ionic equation for the reaction It is not necessary to balance the reaction

1 Mix 1 mL of 0.1M sodium chloride with 1 mL of 0.1M silver nitrate Save the product for step 2

2 Centrifuge the precipitate from step 1 Decant and discard the decantate Add 1 mL of 6M ammonia to the precipitate and agitate

3 Add 2 mL 6M hydrochloric acid to the solution from 3 Test with litmus to be sure the solution is acidic If not acidic, add 1 more mL of the acid

4 Add a tiny bit of calcium oxide to distilled water Test with litmus

5 Put 10 mL of 0.1M potassium iodide solution in a 50 mL beaker Using a 9 volt battery

as a power source and graphite electrodes, allow an electric current to pass through the solution for two minutes Test the solution near the electrodes with litmus

6 Place a small amount of sodium hydrogen carbonate in a test tube Add 1 mL of 0.1 M acetic acid

7 Place 2 mL of oxalic acid solution in a test tube Make a loose ball of a small piece of aluminum foil (2 cm square) and drop it into the solution Use a stirring rod to push it under the solution Wait five minutes and observe

8 Place 1 mL of 0.1M sodium phosphate in a test tube, add 5 mL of 0.1 M hydrochloric acid Feel the outside of the tube for evidence of a reaction

9 Place 2 mL of 0.1 M sulfuric acid in a test tube Add a small spatula of solid sodium bicarbonate

10 Place 2 mL of 0.1M iron III nitrate in a test tube Add several drops of 0.1M potassium thiocyanate solution

11 Place 2.0 mL of 0.1 M aluminum nitrate in a test tube Dropwise, with agitation, add 2

mL of 1.0M sodium hydroxide

12 Place 1 mL of 0.1 M copper II sulfate in a test tube with 3 mL of 0.1 M sodium

hydroxide solution

13 Place 2.0 mL of 0.1M iron III nitrate in a test tube Add 2.0 mL of 0.1M ammonia

14 Place 1.0 mL of 0.1 M barium hydroxide in a test tube Add 5 mL of 0.1 M sulfuric acid

15 Place 5 mL of 0.1M silver nitrate in a test tube Add a small coil of copper wire

Observe after 5 minutes

16 Place 5 mL of 3% hydrogen peroxide in a test tube Add a small amount of solid

manganese IV oxide

Redox Titration: The Standardization of Potassium

be used to determine the concentration of potassium permanganate

Oxalic acid is a strong electrolyte that dissociates completely in water The oxalate ion,

C2O42-, will react quantitatively with permanganate ion, MnO4-, in the presence of strong acid according to the following equation:

MnO4- (aq) + C2O42- (aq)  Mn2+ (aq) + CO2 (g)

The numerical value of Keq for the equilibrium is very large (The reaction goes totally toward the right, very little to the left) When reaction conditions are anywhere near

optimum (in terms of pH and temperature) the reaction can be considered to be

quantitative

Prelab:

1 Balance the equation above

2 Identify what is oxidized and what is reduced

3 Identify the oxidizing agent and the reducing agent

MSDS:

KMnO4 Irritating to body tissues Avoid all body tissue contact

Sodium oxalate Moderately toxic by ingestion and inhalation Corrosive to body

tissues Avoid contact with all body tissues

Sulfuric acid Moderately toxic by ingestion Corrosive to eye, skin, and all other

body tissues Avoid all body tissue contact Very considerable heat generated when diluted with water

Procedure

1 Transfer 200mL of water to a 400mL (or larger) beaker Place the beaker on a hot plate

2 Add 40mL of 6.0M sulfuric acid to the water while stirring with a glass rod

3 Turn on the hot plate Monitor the temperature with a thermometer You will need to heat the acid solution to about 80oC to 90oC Continue with the procedure while the acid

solution is heating (This removes CO2 from the water)

4 Use an analytical balance to mass 0.134g to 0.149g (NO MORE!) of reagent grade sodium oxalate in a weigh boat Record the mass of sodium oxalate to the nearest 0.001g

5 Transfer the sodium oxalate sample to the acid solution You may use a water bottle to facilitate the transfer if necessary Stir until dissolved

6 Rinse a buret with a few milliliters of the potassium permanganate solution Dispose of therinsing down the sink

7 Fill the buret with the permanganate solution above the zero mark Drain the buret until theliquid level is below the zero mark and to clear most of the air from the tip of the buret Mount the buret in a buret clamp on a ring stand and position the buret over the

acid/oxalate solution

11 As the titration approaches its equivalence point the purple color from the permanganate will persist longer and longer before it disappears

12 Slow the rate of titration as the equivalence point is approached

13 Immediately stop the titration when you believe the equivalence point is reached The equivalence point is defined as the point in the titration where the color from the titrant persists for 30 seconds A perfect titration will yield a faint pink solution that persists for

30 seconds

14 If the color fades before the 30 second requirement add more titrant one drop at a time untilthe 30 second requirement is reached

15 Once you are satisfied the equivalence point has been reached record the volume of titrant

16 Run another trial mixing another sample of oxalic acid to verify your results

17 Calculate the molarity of the permanganate solution Be sure to show all calculations in thecalculations area

18 Post your molarity on the class result sheet hanging in the lab

19 Your percent error is done using the average molarity for the class as the accepted value

Clean-up:

1 Pour the remainder of the permanganate back into the stock bottle

2 Rinse the buret with some tap water, rinse again with a hydrogen peroxide solution located in the fume hood and then rinse twice with distilled water

3 Wash the beaker with soap, rinse, rinse and distilled rinse Put on a paper towel at yourstation to dry

Conclusion:

In your conclusion describe why it was necessary to add the sulfuric acid Research some redox reactions that happen in your body and discuss the value of redox reactions in life

The EMF Activity Series

oxidized to an ionic state For example, 2Na + Fe+2  2Na+ + Fe

Although hydrogen has many physical and chemical properties that are similar to nonmetals,

it frequently functions chemically as a metal, and for this reason, it is included in the activity series of metals Its placement indicates that the metals preceding it will displace it from non-oxidizing acids The metals that are found uncombined in nature in large amounts are those that are less active than hydrogen, whereas those metals that are more active than hydrogen are not usually found in the free state Two metals that are exceptions are metallic iron and nickel found in meteorites

The normal test of the chemical activity of an element is its displacing power If the metal can displace another metal from a compound, it may be considered to be more chemically active than the metal it displaces The relative activity of a metal may be determined by observing: 1 - metal reactivity with water: cold, warm, or hot; 2 - metal reactivity with acids: hydrogen producing acids and non-hydrogen producing acids: 3 - metal activity with bases; and 4 - metal reactivity with salt solutions

It should be noted that the more finely divided the state of the metals-powdered form rather than large lumps-the more surface area is exposed, and the greater the activity of the metal Ifthe reaction is heated, the reactivity of the elements and compounds tend to increase

Halogens can also be organized according to their ability to displace other halogens In the reaction between a free halogen X2 and a halide ion Y-, the free halogen gains electrons is reduced to its halide ion X2 + 2e-  2X- The original halide ion is oxidized to the free halogen state 2Y-  Y2 + 2e- The most reactive halogen is the one most easily reduced (most hungry for the electron) To determine if a reaction occurs, a method is needed to identify which halogen is present Halogens dissolve in the nonpolar solvent mineral oil forming different colored solutions Mineral oil does not dissolve in water, but when shaken with an aqueous halogen solution, the halogen is extracted from the water into the mineral oil The color of the mineral oil indicates which halogen is present

Prelab:

Read the entire discussion and procedure

MSDS:

0.1 M Fe(NO3)3 Corrosive to body tissues by contact and inhalation Avoid contact with

skin, eyes and mucous membranes

0.1 M AgNO3 Moderately toxic by ingestion Irritating to body tissues Avoid all body

tissue contact

0.1 M CuSO4 Mildly toxic by ingestion Irritant to skin, eyes and mucous membranes

Avoid contact with body tissues

0.1 M Zn(NO3)2 Slightly toxic by ingestion Corrosive to body tissues Avoid all body

tissue contact

Copper Irritant to body tissues as dust Avoid contact with nitric acid, emits

toxic fumes of nitrogen oxides

Lead Lead as a powder or dust is toxic by ingestion or inhalation Lead and

lead compounds are possible carcinogens Avoid ingestion and

7/24/2024 Page 17 of 116

inhalation Emits highly toxic fumes of Pb when heated Chronic exposure to inorganic lead via inhalation or ingestion can result in accumulation in and damage to the soft tissues and bones

Magnesium Substance not considered hazardous However, not all health aspects of

this substance have been thoroughly investigated

Zinc Substance not considered hazardous However, not all health aspects of

this substance have been thoroughly investigated Inhalation of zinc dust may cause lung irritations Zinc dust can spontaneously combust when in contact with moisture

Calcium Corrosive solid Avoid body tissue contact Violent reaction with water

may evolve explosive hydrogen gas Flammable solid

Sodium Highly corrosive solid, avoid all body tissue contact Will severely burn

skin, eyes, or internal tissues Reacts violently with water releasing hydrogen gas, which will ignite and explode in air

6M HCl Toxic by inhalation and ingestion Severe corrosive to all body tissues,

especially skin and eyes Avoid all body contact

NaBr solution Possible body tissue irritant

NaCl solution Substance not considered hazardous However, not all health aspects of

this substance have been thoroughly investigated

KI solution Substance not considered hazardous However, not all health aspects of

this substance have been thoroughly investigated

Cl2 water Toxic by inhalation and ingestion Very irritating to mucous

membranes This is a weak solution of chlorine gas and water Chlorinegas will slowly leave solution

Br2 water Highly toxic by ingestion and inhalation Severe skin irritant; may

cause burns and irreversible eye damage Strong oxidizer, heat of reaction may ignite combustibles on contact Will react with water or steam to produce toxic and corrosive fumes Extremely hazardous substance

Your lab report must include net ionic equations for each single replacement reaction that occurs Leave plenty of room before the data section

Procedures:

1 For each section below, follow the instructions and perform the reactions

2 Describe each reactant and product

3 If no reaction occurs, write N.R

4 Arrange test tubes in the test tube rack in order as in table 1

Part 1

Reactions of metals with salt solutions

1 Place 1 to 2 mL of each of the following solutions into the designated number of test tubes: iron (III) nitrate - 4, silver nitrate - 4, copper (II) sulfate – 4, and zinc nitrate – 4

2 Obtain the number of strips of each metal as indicated: copper -4, lead - 4,

magnesium - 4, and zinc - 4 Place a strip of metal into each test tube as indicated by the table Allow the solution with metal to sit for at least 15 minutes At the end of 15 minutes, record all changes in the solution and metal in each of the test tubes If no reaction occurs within 20 minutes, write N R rather than a description

3 While waiting for the reactions in the salt solutions to occur, set up the reactions for metals in acid solutions and metals in water

Reactions of metals with acid

Place 1 -2 mL of 6M HCl in each of the designated test tubes Place a strip of each metal intoseparate test tubes of acid Observe immediately for any sign of a reaction occurring Record your observations of the changes

Reactions of metals with water

Place 1-2 mL of water into 3 separate test tubes along with 1 drop of phenolphthalein Place astrip of magnesium into one of the test tubes, a chunk of calcium into one of the test tubes and a piece of sodium into the other test tube At Record observations of any reactions and the changes in the color A pink color indicates a base meaning a reaction has occurred

Part 2 Activity Series for some halogens

If you notice a really strong smell that bothers you, do the following steps in the fume hood

1 As a reference, a rack of test tubes has been set up for you at the front of the room They indicate what color the mineral oil changes when combined with either each halogen or the halide ions

2 Set up 6 test tubes in a test tube rack according to the following table

Clean Up

After all observations are made, empty the test tubes into the corner of the sink, rinse with water, remove the metal to a paper towel at your lab station, wash each test tube, rinse with tap water and do a final rinse with distilled water Turn the clean test tubes upside down in

7/24/2024 Page 19 of 116the test tube rack and leave for the next class

CONCLUSIONS:

1 According to the tests done in lab, list the metals and hydrogen from most active to least active Be sure to also include those metals and hydrogen that were in ionic form in the solutions used In your conclusion give evidence from your results for your conclusion

2 According to the tests done in lab, list the halogens from most active to least active In your conclusion give evidence from your results for your conclusion

3 Were there any tests for the activities of the metals and hydrogen that did not agree with the order of activity according to the EMF activity series? If there were disagreements, why do you think that happened?

4 No error analysis or % error

Heat of Fusion for Ice

Data and Calculations and question only

Discussion:

Melting and freezing behavior are among the characteristic properties that give a puresubstance its unique identity As energy is added, pure solid water (ice) at 0°C changes toliquid water at 0°C

The equation we will use is q=mct where q is heat measure in joules

In this experiment, you will determine the energy (in joules) required to melt ice You willthen determine an experimental value for the molar heat of fusion for ice (in kJ/mol) andcompare it to the accepted value Excess ice will be added to warm water, at a knowntemperature, in a Styrofoam cup Heat from the warm water will be used to warm the ice toits melting point, 0oC, to melt the ice, and then to warm the resulting liquid to sometemperature above 0oC

The heat balance for the system can be defined by the following equation:

(c(ice) •t •mice) Heat absorbed by the ice

+ (miceHf) Heat it takes to melt the ice

+ (c(water) •  t •m(water from melt)) Heat absorbed by the melted ice

c(water) •t •m(hot water) Heat lost by the hot water

where c is specific heat capacity (one value for liquid water another for ice) , m is mass in

grams, Hf is the heat of fusion for ice, and t is the change in temperature (each t should

be unique) The minus sign is used on the left because heat is being lost For liquid water, c

is 4.18 J/g°C For ice, c is 2.03J/goC

Prelab:

1 Calculate the amount of heat necessary to heat 15.00 g ice from -20 to 0 °C

2 Calculate the mass of water when 7700 J of heat is added to water at an initialtemperature of 29° which increases 69 degrees

4 Once the water is hot, use a 100-mL graduated cylinder to transfer 100.0 mL of the hotwater to the styrofoam cup Use a balance to determine the mass of the water Usebeaker tongs and/or “hothand” glove to make the transfer Place the thermometer in theStyrofoam cup containing the hot water and allow the temperature reading to stabilize.Record the temperature reading as “initial hot water temperature.”

5 When ready, start adding ice to the hot water Stir the mixture continuously with thethermometer Continue to add ice as the ice melts to maintain a significant excess of ice

6 Once the temperature goes below 10oC quickly remove any remaining ice from theStyrofoam cup Record the minimum observed temperature as the “final system

temperature.”

7/24/2024 Page 21 of 116

7 Record the mass of the water after the melt

Data and Calculations

Be sure to collect the following data

Initial ice temperature

Initial hot water temperature, t1

Final system temperature, t2

Change in temperature of the hot water, t

Change in temperature of melted water, t

Change in temperature of ice before melting, t

Final water mass

Initial water mass

Mass of melt

SHOW YOUR CALCULATIONS for the following:

Mass of ice melted

Heat released by the hot water as it cooled

Heat gained by solid ice as it warmed from its initial temp to its melt temp

Heat gained by liquid melt as it warmed from its melt temp to final system temp

J/g ice melted (heat of fusion)

kJ/mol ice melted (molar heat of fusion)

Percent error (6.03 kJ/mol is the accepted value)

Questions:

1 Research the heat of fusion of paraffin wax How would it be useful for a

homeowner’s wall to be filled with blocks of paraffin wax?

2 Go to this website, what kinds of PCM’s are used in gloves?

http://www.textileworld.com/Articles/2004/March/Features/Phase_Change_Materials.html

Additivity of Heats of Reaction: Hess’s Law

Full writeup

In this experiment, you will use a Styrofoam-cup calorimeter to measure the heat released bythree reactions One of the reactions is the same as the combination of the other tworeactions Therefore, according to Hess’s Law, the heat of reaction of the one reaction should

be equal to the sum of the heats of reaction for the other two This concept is sometimes

referred to as the additivity of heats of reaction The primary objective of this experiment is

to confirm this law The reactions we will use in this experiment are: (Write equations for

each one including state of matter for Prelab)

(1) The dissolution of solid sodium hydroxide H1 = ?

(2) Solid sodium hydroxide reacts with aqueous hydrochloric acid H2 = ?

3) Solutions of aqueous sodium hydroxide and hydrochloric acid react H3 = ?

You will use a Styrofoam cup as a calorimeter For purposes of this experiment, you mayassume that the heat loss to the calorimeter and the surrounding air is negligible Even if heat

is lost to either of these, it is a fairly constant factor in each part of the experiment, and haslittle effect on the final results

MSDS:

NaOH Highly toxic by ingestion, inhalation, or skin absorption

Extremely corrosive to body tissues Causes severe eye burns.Avoid all body tissue contact

0.50 M and 1.0 M HCl Toxic by inhalation and ingestion Severe corrosive to all body

tissues, especially skin and eyes Avoid all body contact

Procedure

Reaction 1

1 Measure out 100.0 mL of water into the Styrofoam cup Place the thermometer into thesolution Allow the temperature reading to stabilize and record the temperature as the

“initial temperature.” Be sure to record the mass of the water

2 Weigh out about 2 grams of solid sodium hydroxide, NaOH, and record the mass to thenearest 0.001 g Since sodium hydroxide readily picks up moisture from the air, it isnecessary to weigh it and proceed to the next step without delay Caution: Handle theNaOH and resulting solution with care

3 Add the NaOH to the water in the Styrofoam cup and swirl the cup to aid dissolution.Monitor the temperature increase Record the maximum temperature as the “finaltemperature.”

4 Rinse and dry the thermometer and Styrofoam cup Dispose of the solution in the beaker

in the fume hood

Reaction 2

5 Repeat the steps for reaction 1, using 50.0 mL of 1.0 M hydrochloric acid added to 50.0

mL of distilled water instead of water Use approximately the same amount of solidNaOH as before Caution: Handle the HCl solution and NaOH solid with care Recordthe mass of the water before you add the solid NaOH

Reaction 3

6 Run another trial using 50.0 mL 1.0 M HCl in place of water and 50.0 mL 1.0 M NaOH

in place of solid NaOH Record the initial temperature of the HCl and the finaltemperature of the mixture Record the mass of the two solutions together

7/24/2024 Page 23 of 116

Processing Data

1 Determine the temperature change, t, for each reaction

2 Calculate the heat released by each reaction, q,(Convert joules to kJ in your final answer.)

3 Calculate moles of NaOH used in each reaction

4 Use the results of the Step 4 and Step 5 calculations to determine H/mol NaOH in each

of the three reactions

5 Use Hess’s law 1 and 2 should add up to 3 Use 3 as the accepted value Calculate percent error

6 Record your value on the class data sheet in the lab Report your data and the class average data

Heat of Combustion of a metal-an inquiry based approach

Data and Calculations and questions only

Discussion:

In this experiment you will use Hess’ Law of the additivity of reaction heats to determine the heat of reaction for a reaction that is difficult to measure directly – the combustion of either magnesium or zinc The combustion of a metal with a 2+ oxidation state is represented by the following equation:

M (s) + ½ O2 (g)  MO (s)This equation can be obtained by creatively combining equations (1), (2), and (3)

(1) MO (s) + 2HCl (aq) 

(2) M (s) + 2HCl (aq) 

(3) H2 (g) + ½ O2 (g)  H2O (l)

The heats of reaction for equations (1) and (2) will be determined in this experiment

H/mol for reaction (3) is –285.8 kJ/mol

Prelab: Find the 

H f for each reactant in equations 1, 2 and 3 Read all lab procedures.MSDS:

MgO Inhalation may cause respiratory irritation Slight eye irritant

HCl Highly toxic by inhalation and ingestion Severe corrosive to all body tissues, especially skin and eyes Avoid all body contact.

Mg Flammable solid Substance not considered hazardous However, not all health

aspects of this substance have been thoroughly investigated

Zn Inhalation of zinc dust may cause lung irritations Zinc dust can spontaneously

combust when in contact with moisture

ZnO Moderately toxic by ingestion and inhalation Body tissue irritant Avoid all body

Part II Hydrochloric Acid Plus M

1) You will need approx 0.5 ±0.25g g of M and approximately 100 g ± 25 g of 6M HCl2) Determine the mass you will use of the M and the HCl Write a procedure that willdetermine the H for the reaction #2 above per mole of M

3) Do the stoichiometry necessary to find the limiting reactant and amount of excess reagentremaining

4) Have your teacher approve both the stoichiometry and the procedure you wrote Afterapproval perform your experiment and collect the data

7/24/2024 Page 25 of 116

Processing the Data

1 Calculate T for each reaction

2 Calculate the heat using mcat

3 Calculate the moles of MO and M used

4 Calculate the H per mole of MO for the first reaction and the H per mole of

M for the second reaction Record these values on the data sheet

5 Determine the heat of combustion for the metal by rearranging the equations1-3 above using Hess’s law Show the correct rearrangement as part of the calculations

6 Determine the percent error for your experimental result Look up the heat ofreaction for oxidation of zinc or magnesium and use that as the theoretical

7 Share your data with your classmates and do a 2nd percent error using the classaverage for your metal as the expected

Questions:

1 Research magnesium decoy flares and describe how modern Stinger missile systems can tell the difference between aircraft engines and these flares

2 Describe the difference between the H for each metal and

describe why one metal would have a higher H than the other

VSEPR and Molecular Geometry

Copy this table in your lab notebook, no formal writeup

Design the Lewis structure and its molecular geometry on a scratch piece of paper and then draw it in the correct orientation in your lab notebook Decide whether the molecule is polar

or non polar Not the bond but the molecule

Formula Lewis Structure Bonding

7/24/2024 Page 27 of 116

Formation of a Coordination Complex of Copper (II)

Written observations in lab notebook

Discussion

The class of substances referred to as coordination compounds generally contains a central metal atom, to which a fixed number of molecules or ions (called ligands) are coordinately covalently bonded in a characteristic geometry Coordination complexes are very important

in both inorganic and biological systems For example, the molecule heme in the bearing protein hemoglobin contains coordinated iron atoms Chlorophyll, the molecule that enables plants to carry on photosynthesis, is a coordination compound of magnesium

oxygen-In general, coordination compounds contain a central metal ion that is bound to several other molecules or ions by coordinate covalent bonds For example, the compound to

be synthesized in this experiment, tetramminecopper (II) sulfate, consists of a copper (II) ion surrounded by four coordinated ammonia molecules The unshared pair of electrons on the nitrogen atom of the ammonia molecule is used in forming the coordinate bond to the copper (II) ion In other words, the ammonia acts as a lewis base to the copper’s lewis acid

One property of most transition metal coordination compounds that is especially striking is their color Generally the coordinate bond between the metal ion ad the ligand is formed using empty low-lying d-orbitals of the metal ion Transitions of electrons within the

d orbitals correspond to wavelengths of visible light, and generally these transitions are very intense Coordination complexes of metal ions are some of the most beautifully colored chemical substances known; frequently they are used as pigments as paints

Prelab: Read the procedure; write the formula for tetraaminecopper (II) sulfate.

MSDS:

CuSO4 Mildly toxic by ingestion Irritant to skin, eyes and mucous membranes Avoid

contact with body tissues

NH4OH Liquid and vapor are strongly irritating to skin, eyes, and mucous membranes

Vapor extremely irritating to eyes May cause blindness Moderately toxic by ingestion or inhalation

Et-OH Toxic by ingestion and inhalation Body tissue irritant Avoid all body tissue

contact Denatured with isopropanol and methanol Not for human consumption.Flammable liquid

Procedure:

1 Weigh out approximately 1.0 g of copper II sulfate pentahydrate Record the mass

2 Dissolve the copper salt in approximately 10 mL of distilled water in a beaker or flask Stir thoroughly to make certain that all the copper salt has dissolved before proceeding Record the color of the solution at this point

3 Transfer the copper solution to the exhaust hood and with constant stirring; slowly add 5 mL of concentrated ammonia The first portion of ammonia added will cause a light blue precipitate of copper II hydroxide to form But upon adding more

ammonia, this precipitate will dissolve as the ammonia complex forms Record the color of the mixture after all of the ammonia has been added

4 To decrease the solubility of the tetramminecopper (II) complex, add approximately

10 mL of ethyl alcohol with stirring A deep blue solid should precipitate Code word

“cinnabon”

5 Allow the precipitate to stand for 5 minutes and then filter the precipitate

6 While in the filter paper, wash the precipitate with 2-5 mL portions of alcohol and stir

7/24/2024 Page 29 of 116

7 Remove the filter paper and allow the filter paper to dry

Clean up: Filtrate can be put down the sink with excess water Dried precipitate can be thrown into the garbage can Clean all glassware with soap and water, rinse, rinse distilled rinse Wash hands before leaving the lab

Kinetics of a Reaction An Iodine Clock

The rate of this reaction can be defined by the following equation:

Rate = k[IO3 -]x[HSO3 -]y

Where: k is a temperature dependent rate constant

[IO3-] is the initial concentration of iodate[HSO3-] is the initial concentration of bisulfiteand x and y are the reaction orders of iodate and bisulfite respectivelyThe reaction order values for a set of reactants are totally unrelated to the stoichiometric coefficients In all cases reaction order values must be determined experimentally On edmodo there is a link to a video and a paper handout of how to solve for the exponents if you don’t remember how to do logs

Prelab: Read all the procedures and be ready to hand me a slip of paper 3 cm square with your name on it in order to get into the lab

MSDS:

KIO3 Substance not considered hazardous However, not all health aspects of this

substance have been thoroughly investigated

NaHSO3 Mild body tissue irritant Avoid contact with body tissues

Starch Substance not considered hazardous However, not all health aspects of this

substance have been thoroughly investigated

7/24/2024 Page 31 of 116

Procedure

1 Obtain three 100 or 150mL beakers and label them “KIO3”, “NaHSO3”, and “Starch”

2 Obtain ~75mL of the 0.04M KIO3 solution, ~75mL of the 0.04M NaHSO3 in 0.04M

H2SO4 solution, and about 50mL of the starch solution in the labeled beakers

3 Follow the trial table below to prepare the reaction mixture for each trial Use syringes tomeasure out the correct amount of each solution A clean 100mL graduated cylinder can

be used for water and starch measurements The water and starch may be combined in

the 100mL graduated cylinder during measurements Add the contents of the

graduated cylinder to an Erlenmeyer flask and then add the KIO3 Always add the KIO 3 last when you start the timer Notice the total volume for each trial is 100mL

4 In each trial the water, starch, and NaHSO3 should be added to a beaker One student must then start the timer when the KIO3 is added For each trial record the time in seconds required for the solution to change after the KIO3 is added

5 After each trial, dispose of the reaction mixture in the sink and rinse the beaker

thoroughly with tap water

6 You need to calculate the concentration of each chemical for each of the three trials, the exponents for the rate law (they will be decimals, don’t round) and the value of k

Cleanup: Take all the syringes apart, rinse with water and lay on a paper towel at your station to dry Rinse all the glassware twice with tap water and leave at your station to dry

Trial Water Starch NaHSO H 2 SO 4 3 in

KIO 3 (always add last)

1 Which of the steps in the proposed mechanism is the rate determining step? Why?

2 Given your experimentally determined values for the reaction orders x and y, what would be the expected reaction time if the following solution were timed: 20mL KIO3, 5mL NaHSO3, 5mL starch, and 70mL water?

Where did the Crystal Violet go?

Full Writeup

Central Challenge

The purpose of this laboratory activity is to determine the rate law for the reaction

of crystal violet (CV) and sodium hydroxide (NaOH) In Part 1 of the investigation, you willprepare dilutions of a stock CV solution to generate a Beer’s law calibration curve for CV

In Part 2 of the investigation, you will perform a reaction of CV with NaOH while

monitoring in real time the concentration of CV remaining This laboratory investigation willillustrate a variety of science concepts because determining the rate law for the reaction of

CV with NaOH requires you to use graphical analysis and a simplifying approximation that leads to a pseudo-rate law while also integrating prior chemistry knowledge involving spectroscopy, Beer’s law, solution dilution, calibration curves, and chemical kinetics

Context for This Investigation

If you’re making something, you might think making it to last would always be a good thing.But what if you’re making a pesticide with known detrimental impacts on human health? Then you may only want it to stay intact for a few days after it has been applied to crops before it decomposes into what often are less harmful products If its molecules stay intact for too long, the pesticide can persist in the environment and build up in drinking water In

2000, over 20 million kilograms of the pesticide 1,3-dichloropropene (1,3-D) were applied tocrops in the United States Scientists investigated the rate of decomposition of 1,3-D in acidic, basic, and neutral solutions as well as in soil For each case, they generated plots of the amount of intact 1,3-D persisting versus time and found that the reaction could be

characterized as pseudo first-order Knowing the order of the reaction allowed them to determine the half-life of intact 1,3-D In acidic media, they found that the half-life for the decomposition of 1,3-D was about eight days, but in the presence of excess NaOH the half-life was reduced to about four days Experimentally determined data like this is vital to the ability of society to use chemicals wisely in improving food production, while not

endangering the end consumers or the people who work with the chemicals during the growing process The Beer’s law employs the use of a colorimeter (or spectrophotometer) to obtain a calibration curve that is used to convert raw absorption data from a colorimeter (or spectrophotometer) to molar concentration of a chemical in solution In this investigation, you will first use a colorimeter (or spectrophotometer) to generate a calibration curve for a chemical (CV) and then use the colorimeter (or spectrophotometer) to follow the change in the concentration of CV as it reacts with NaOH By recording these changes through time and analyzing them graphically, you will be able to obtain the rate law of the reaction, which may be used to predict the behavior of the system under different experimental conditions without doing the actual experiments

PreLab questions Day 1

1 Answer the following questions about the selection of a wavelength for your experiment

a Based on the absorption spectrum of 25 μM crystal violet in Figure 1 and taking into M crystal violet in Figure 1 and taking into account the considerations that follow, what wavelength should you use for the Beer’s law calibration curve and subsequent reaction of CV with NaOH? Please explain your answer

b Simulate the instrument readings you will get in Part 1 of the experiment by doing the following: Trace Figure 1 onto your own paper Draw a vertical line at the wavelength you have chosen, intersecting the absorbance curve at that wavelength Where your vertical line intersects the absorbance curve is the absorbance value your instrument should read for the stock 25 μM crystal violet in Figure 1 and taking into M CV solution Keeping in mind Beer’s law from

Equation 1, and being mindful that the wavelength and path length are fixed, draw X’s

7/24/2024 Page 33 of 116

on your vertical line where you expect the absorbance values will be for the diluted solutions you prepare in Question 2 Use appropriate ratios of concentrations to

determine where on the vertical line to make your marks

2 A calibration curve requires the preparation of a set of known concentrations of CV, whichare usually prepared by diluting a stock solution whose concentration is known Describe how to prepare 10 mL of a 5-, 10-, 15-, and 20- μM crystal violet in Figure 1 and taking into M CV solution using a 25 μM crystal violet in Figure 1 and taking into M CV stock solution

3 During the reaction of CV with NaOH, do you expect the colorimeter’s (or

spectrophotometer’s) absorbance reading to change? How do you expect it to change if such a change is anticipated (i.e., increase, decrease, or no change) as the reaction

proceeds? Explain your reasoning

4 Answer the following questions for a reaction of CV with NaOH in these two scenarios: a solution with a 1:1 NaOH:CV mole ratio and a solution similar to what you will be using with a 1000:1 NaOH:CV mole ratio

a Using your prior knowledge of reaction stoichiometry, what is the final percentage of each reactant remaining if each reaction went to completion? Show work and reasoning

to justify your answer

5 Using the kinetics chapter in your textbook and websites like “Chemical Kinetics –

Integrated rate laws” http://www.chm.davidson.edu/vce/kinetics/IntegratedRateLaws.html,describe the graphical analysis that can be done to determine the order (considering only 0th, 1st, or 2nd order) and the value of the pseudo-rate constant, k*, of a chemical reactionfrom concentration data collected through time

6 Based on your answer to Questions 3–5, design an experiment for the reaction of CV with NaOH and describe the subsequent data analysis to accomplish the Central Challenge, the determination of the value of (i) w, the order with respect to CV and (ii) k*, the pseudo-rate constant found in the rate law in Equation 3 For simplicity, use 10 mL for the

combined volume of CV and NaOH because it is a bit more than enough to fill cuvettes appropriately

7 Answer the following questions after examining Figure 3 to address the issue of when to stop collecting data

a For early parts of the three different reactions in Figure 3, all three curves seem

relatively linear with different slopes But as the reactions progress through time, at roughly what concentration level would you say some graphs start to look nonlinear?

b Given that you don’t yet know the order of the reaction of CV with NaOH, how might Figure 3 help you to decide when to stop collecting data? Hint: Think in terms of percent completion instead of concentration

Explanation to help your understanding: Read before you come to class.

For a fixed concentration of solute and a fixed path length (e.g., fixed cuvette width), the amount of light absorbed by a solution varies directly with the absorptivity constant of the solute Figure 1 below shows the visible light absorbance spectrum of CV for a fixed, 25 μM crystal violet in Figure 1 and taking into M,concentration of CV and a fixed, 1.0 cm, path length Because concentration and path length are both kept constant, Figure 1 reveals how the absorptivity constant for CV varies with the wavelength of light passing through the solution Figure 1 was generated by a

Figure 1 The visible spectrum of a 25 μM CV solutionM CV solution

If we still keep the path length fixed, but now choose only one particular wavelength of light to pass through the solution, thereby fixing the

absorptivity constant, students can then observe how the absorbance of light

at that wavelength changes as they change the concentration of CV Under these conditions, Beer’s law describes a straight-line relationship for a graph

of absorbance versus solute concentration whose slope is simply the product

of the molar absorptivity constant and path length

In the reaction of CV and sodium hydroxide (see Figure 2), the dye’s color willfade as it reacts with sodium hydroxide A colorimeter (or

spectrophotometer) will be used to follow the disappearance through time of

CV by measuring the absorbance of a solution of CV during its reaction with NaOH The raw absorbance measurements from the colorimeter (or

spectrophotometer) can be transformed to molar concentration of CV via the use of a Beer’s law calibration curve

Figure 2 Chemical structures in the reaction in this laboratory activity

The net ionic equation for the reaction can be written as

CV+ (aq) + OH–(aq) → CVOH (aq)

7/24/2024 Page 35 of 116rate = k [CV+]w [OH–]z Equation 2

where k is the rate constant while w and z are the order of the reaction with respect to CV+ and OH-, respectively Under certain experimental conditions (see prelab Question 4), the rate law in Equation 2 simplifies to the following equation:

and k* is the rate constant Equation 3 is referred to as the rate law, since it is an approximation to Equation 2, the actual rate law, and significantly simplifies the analysis

pseudo-A differential rate law describes the rate of a chemical reaction as a function

of the concentration of the reactants, while an integrated rate law describes the concentration of a reactant as a function of time; both types of rate laws are related to each other by the use of calculus Equation 3 is a differential rate law, in which a graphical analysis of the corresponding integrated rate law can be used to determine the value of the parameters in Equation 3 using least-squares linear regression analysis The degree or extent of linear fit may be evaluated using the coefficient of determination (or square of the correlation coefficient), i.e., it may be used to identify the graph that has a linear relationship

Figure 3 shows concentration data plotted versus time for three different

hypothetical chemical reactions From plots like these and knowledge of

integrated rate laws found in your text or at online resources, one can

determine the exponents in the rate law equation.

hypothetical chemical reactions — 0th order (blue line), 1st order (red line), and 2nd order (yellow line)

All reactions have the same numerical value for their initial reactant

concentration and the rate constant

approximation to Equation 2

The analysis described in prelab Question 6 requires that you know the concentration of CV throughout the course of the reaction The

concentration of CV can be obtained from raw absorbance data by

applying the Beer’s law calibration curve formula you obtained previously.Prelab Question 6 asks you to design an experiment to determine the value of w and k* found in Equations 3 and 4 Both w and k* can be

determined by making appropriate plots of your data from the reaction of

CV with NaOH and checking for linear relationships

Use your answer to prelab Question 8 to decide during the experiment when to stop collecting absorbance data to get the clearest distinction between 0th-, 1st-, and 2nd-order reactions during your postlab graphical analysis

concentrations of all ions at equilibrium: [FeSCN2 +]eq, [SCN–]eq, and [Fe3 +]eq Since the complex is intensely colored, its concentration is conveniently measured using a

spectrophotometer You will prepare several mixtures containing different initial amounts ofiron III nitrate and potassium thiocyanate and will then use a spectrophotometer to measure the absorbance as an indication of the concentration of the red product From the initial concentrations of the reactants taken in each mixture and the concentration of the product present at equilibrium in each mixture, you can calculate the concentration of the reactants at equilibrium and thus the Kc

Prelab: Read the entire lab procedure, and use a graphing program to build and print a

calibration curve as the procedure directs you to do To enter the lab you must place your printed graph on top your head and whisper “Doctor Who” to get in

MSDS:

Fe(NO3)3 Corrosive to body tissues by contact and inhalation Avoid contact with skin, eyes

and mucous membranes Acidified with Nitric acid

KSCN Slightly toxic by ingestion Irritating to body tissues Avoid all body tissue

contact Contact with acids or heat may liberate poisonous hydrogen cyanide gas

Record the absorbance for each test tube at a wavelength of 450 nm, transferring the sample

to the cuvette and rinsing the cuvette between readings

Prepare a standard solution with 9 mL of 0.200 M Fe(NO3)3(aq) (note this is different than before) and 1 mL 0.002 M KSCN Record the absorbance of that solution

Using the following data, construct a calibration curve It must be a scatter plot with a line ofbest fit There is a podcast that illustrates the process using excel

[Iron III thiocyanate complex] M Absorbance

2 Calculate the initial concentrations of [Fe3+] and [SCN-] present in each of the 5 tubes

3 Calculate the equilibrium concentrations of [Fe3+] and [SCN-] present in each of the 5 tubes

Calculate a Keq for each tube; calculate an average Keq and the standard deviation

Record your values for Keq for each tube on the class data sheet

Cleanup: Throw away any disposable pipets Wash all glassware with soap, rinse 2X with

tap water and once with distilled water Put all glassware at your lab station to dry

Conclusion: Compare your data to the class average data Discuss conditions under which the Keq would be different than the ones you found in lab using the same quantities as identified in the lab

7/24/2024 Page 39 of 116

Entropy of a Reaction

NO WRITEUP REQUIRED

Discussion:

An endothermic process or reaction absorbs energy in the form of heat (endergonic processes

or reactions absorb energy, not necessarily as heat) Examples of endothermic processes include the melting of ice and the depressurization of a pressurized can In both processes, heat is absorbed from the environment You could record the temperature change using a thermometer or by feeling the reaction with your hand The reaction between citric acid and baking soda is a highly safe example of an endothermic reaction, commonly used as a chemistry demonstration Do you want a colder reaction? Solid barium hydroxide

octahydrate reacted with solid ammonium thiocyanate produces barium thiocyanate,

ammonia gas, and liquid water This reaction gets down to -20°C or -30°C, which is more than cold enough to freeze water It's also cold enough to give you frostbite, so be careful! Here's what you need to use this reaction:

15g barium hydroxide octahydrate

9g ammonium thiocyanate (or could use ammonium nitrate or ammonium chloride)

50-ml beaker

Neutral litmus paper

stirring rod

Prelab:

1 Read the discussion and procedure Be prepared to answer these questions

2 Explain how this reaction increases entropy

3 Is the change in enthalpy for the reaction going to be positive or negative? Explain your reasoning

4 Why are you using litmus?

Procedure

1 Pour the barium hydroxide and ammonium thiocyanate into the beaker

2 Stir the mixture

3 The odor of ammonia should become evident within about 30 seconds If you hold a piece of dampened litmus paper over the reaction you can watch a color change showing that the gas produced by the reaction is basic

4 Liquid will be produced, which will freeze into a slush as the reaction proceeds

5 If you set the flask on a damp block of wood or piece of cardboard while performing the reaction you can freeze the bottom of the flask to the wood or paper You can touch the outside of the flask, but don't hold it in your hand while performing the reaction

6 After the demonstration is completed, the contents of the flask can be washed down the drain with water Do not drink the contents of the flask Avoid skin contact If you get any solution on your skin, rinse it off with water

Catalytic Converter—Hot Copper Catalysis

Discussion

Catalytic converters are used in automobiles to reduce emissions of unburned hydrocarbons These unburned hydrocarbons result from incomplete combustion of the gasoline fuel Catalytic converters contain rare metals such as platinum and rhodium that catalyze the combustion of hydrocarbons with the oxygen that remains in the engine’s exhaust stream This combustion generates heat that, in turn, makes the continued combustion of the unburned hydrocarbons more efficient

In this demonstration you will observe the catalyzed combustion of a hydrocarbon, namely 2-propanol, sometimes called isopropyl alcohol, on the surface of a metal catalyst A hot copper penny is used to provide the reaction surface

2-propanol can react with oxygen to form acetone and water according to the following equation:

2CH3CHOHCH3 + O2  2CH3COCH3 + H2O (equation 1)

This reaction is thermodynamically permitted but very slow even at elevated temperatures To make the reaction go a catalyst is needed Hot copper(II)oxide will do the trick When a pre-1982 penny (almost entirely pure copper) is heated in a burner flame copper(II)oxide forms on the surface of the penny according

to the following equation:

2Cu + O2 + heat  2CuO (equation 2)

When the hot copper(II)oxide is introduced into 2-propanol vapor with oxygen present the following

exothermic reaction occurs:

CH3CHOHCH3 + CuO  CH3COCH3 + Cu + H2O + heat (equation 3)

The liberated copper metal reacts further with oxygen to make copper(II)oxide which reacts further with propanol and so forth and so on The heat generated by the reaction described by equation 3 is adequate to provide the heat needed by the reaction described by equation 2 This series of reactions proceed at an

2-acceptable rate as long as the temperature of the penny is high enough

Pre-Lab Questions

1 Many states conduct periodic emissions tests on vehicles These tests should not be conducted when the engine is cold but only after the engine has been started and allowed to warm to normal operating temperature Speculate on why this is so

2 One of the first devices used to combat automobile pollution was an “air pump.” This

pump would deliver outside air directly into the exhaust manifold of a running engine

Speculate on how this helped to reduce the emission of unburned fuel molecules