The chemical properties of the following compounds, dissolved in water, areinvestigated in Part A of this experiment: Sodium carbonate Na2CO3aq Magnesium sulfate MgSO4aq Ammonium chlorid
Trang 1Experiment 2
Identification of
a Compound: Chemical Properties
• To identify a compound on the basis of its chemical properties
• To design a systematic procedure for determining the presence of a particularcompound in aqueous solution
The following techniques are used in the Experimental Procedure:
Techniques
Introduction
Chemists, and scientists in general, develop and design experiments in an attempt tounderstand, explain, and predict various chemical phenomena Carefully controlled(laboratory) conditions are needed to minimize the many parameters that affect theobservations Chemists organize and categorize their data and then systematicallyanalyze the data to reach some conclusion; often, the conclusion may be to carefullyplan more experiments!
It is presumptuous to believe that a chemist must know the result of an ment before it is ever attempted; most often, an experiment is designed to determinethe presence or absence of a substance or to determine or measure a parameter A
experi-goal of the environmental or synthesis research chemist is, for example, to separatethe substances of a reaction mixture (one generated in the laboratory or one found innature) and then identify each substance through a systematic, or sometimes trial- and-error, study of their chemical and physical properties As you will experience
later, Experiments 37–39 are designed to identify a speci c ion (by taking advantage
of its unique chemical properties) in a mixture of ions through a systematic sequence
of analyses
In this experiment, you will observe chemical reactions that are characteristic ofvarious compounds under controlled conditions After collecting and organizing yourdata, you will be given an unknown compound, one that you have previously investi-gated The interpretations of the collected data will assist you in identifying yourcompound
What observations will you be looking for? Chemical changes are generallyaccompanied by one or more of the following:
• A gas is evolved This evolution may be quite rapid, or it may be a “ zzing”
sound (Figure 2.1, page 54)
Substance: a pure element or compound having a unique set of chemical and physical properties Trial-and-error study: a method that is often used to seek a pattern in the accumulated data
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Trang 2• A precipitate appears (or disappears) The nature of the precipitate is important.
It may be crystalline, it may have color or it may merely cloud the solution
• Heat may be evolved or absorbed The reaction vessel becomes warm if the
reaction is exothermic or cools if the reaction is endothermic
• A color change occurs A substance added to the system may cause a color
change
• A change in odor is detected The odor of a substance may appear, disappear,
or become more intense during the course of a chemical reaction
The chemical properties of the following compounds, dissolved in water, areinvestigated in Part A of this experiment:
Sodium carbonate Na2CO3(aq)
Magnesium sulfate MgSO4(aq)
Ammonium chloride NH4Cl(aq)
The following test reagents are used to identify and characterize these compounds:
Silver nitrate AgNO3(aq)
Hydrochloric acid HCl(aq)
In Part B of this experiment, the chemical properties of ve compounds in aqueoussolutions, labeled 1 through 5, are investigated with three reagents labeled A, B, and C.Chemical tests will be performed with these eight solutions An unknown will then beissued and matched with one of the solutions, labeled 1 through 5
Procedure Overview: In Part A, a series of tests for the chemical properties of
known compounds in aqueous solutions are conducted A similar series of tests areconducted on an unknown set of compounds in Part B In each case, an unknown com-pound is identi ed on the basis of the chemical properties observed
You should discuss and interpret your observations on the known chemicaltests with a partner, but each of you should analyze your own unknown compound Ateach circled superscript1–7 in the procedure, stop and record your observation on the
Report Sheet.
To organize your work, you will conduct a test on each known compound
in the ve aqueous solutions and the unknown compound with a single test reagent.The Report Sheet provides a “reaction matrix” for you to describe your observations.
Because the space is limited, you may want to devise codes such as the following:
• p—precipitate ⫹ color • g—gas, no odor
• c—cloudy ⫹ color • go—gas, odor
• nr—no reaction
1 Observations with silver nitrate test reagent
a Use a permanent marker to label ve small, clean test tubes (Figure 2.2a) or
set up a clean 24-well plate (Figure 2.2b) Ask your instructor which setupyou should use Place 5–10 drops of each of the ve “known” solutions into thelabeled test tubes (or wells A1–A5)
b Use a dropper pipet (or a dropper bottle) to deliver the silver nitrate solution.
(Caution: AgNO 3 forms black stains on the skin The stain, caused by silver metal, causes no harm.) If after adding several drops you observe a chemicalchange, then add 5–10 drops to see if there are additional changes Record yourobservations in the matrix on the Report Sheet.1 Save your test solutions for
54 Identification of a Compound: Chemical Properties
Figure 2.1 A reaction mixture
of NaHCO 3 (aq) and HCl(aq)
produces CO 2 gas
Reagent: a solid chemical or a
solution having a known
A mix of AgNO 3 and NaCl solutions
produce a white AgCl precipitate.
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Trang 3Part A.4 Write the formula for each precipitate that forms Ask your lab
instruc-tor for assistance For example, a mixture of NaCl(aq) and AgNO3(aq) produces AgCl(s) as a precipitate The insolubility of AgCl is noted in Appendix G.
2 Observations with sodium hydroxide test reagent
a Use a permanent marker to label ve additional small, clean test tubes
(Figure 2.3) Place 5–10 drops of each of the ve “known” solutions into thissecond set of labeled test tubes (or wells B1–B5, Figure 2.2b)
b To each of these solutions, slowly add 5–10 drops of the sodium hydroxide
solu-tion; make observations as you add the solution Check to see if a gas evolves inany of the tests Check for odor What is the nature of any precipitates that form?
Observe closely.2 Save your test solutions for reference in Part A.4 Write theformula for each of the precipitates that formed
3 Observations with hydrochloric acid test reagent
a Use a permanent marker to label ve additional small, clean test tubes
(Figure 2.4) Place 5–10 drops of each of the ve “known” solutions into thisthird set of labeled test tubes (or wells C1–C5, Figure 2.2b)
b Slowly add 5–10 drops of the hydrochloric test reagent to the solutions and
record your observations Check to see if any gas is evolved Check for odor
Observe closely.3 Save your test solutions for reference in Part A.4 Write theformula for any compound that forms
Appendix G Appendix G
Figure 2.2a Arrangement of test
tubes for testing with the silver nitrate reagent
Figure 2.4 Arrangement of test
tubes for testing with the hydrochloric acid reagent
Figure 2.3 Arrangement of test
tubes for testing with the sodium hydroxide reagent
Figure 2.2b Arrangement of test solutions in the 24-well plate for testing salts
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Trang 44 Identi cation of unknown Obtain an unknown for Part A from your laboratory
instructor Repeat the three tests with the reagents in Parts A.1, 2, and 3 on yourunknown On the basis of the data from the “known” solutions (collected and sum-marized in the Report Sheet matrix) and that of your unknown solution, identify
the compound in your unknown solution.4
CLEANUP: Rinse the test tubes or well plate twice with tap water and twice with
deionized water Discard each rinse in the Waste Salts container
The design of the experiment in Part B is similar to that of Part A Therefore, 15 cleantest tubes or a clean 24-well plate is necessary
1 Preparation of solutions On the reagent shelf are ve solutions labeled 1
through 5, each containing a different compound Use small clean test tubes or thewell plate as your testing laboratory About 1 mL of each test solution is necessaryfor analysis
2 Preparation of reagents Also on the reagent shelf are three reagents labeled A,
B, and C Use a dropper pipet (or dropper bottle) or a Beral pipet to deliverreagents A through C to the solutions
3 Testing the solutions
a Test each of the ve solutions with drops (and then excess drops) of reagent A.
If, after adding several drops, you observe a chemical change, add 5–10 dropsmore to see if there are additional changes Observe closely and describe anyevidence of chemical change; record your observations.5
b With a fresh set of solutions 1–5 in clean test tubes (or wells), test each with
reagent B.6 Repeat with reagent C.7
4 Identi cation of unknown An unknown solution will be issued that is one of the
ve solutions from Part B.1 On the basis of the data in your reaction matrix andthe data you have collected, identify your unknown as one of the ve solutions
CLEANUP: Rinse the test tubes or well plate twice with tap water and twice with
deionized water Discard each rinse in the Waste Salts container
This experiment will enable you to better understand the importance of “separation andidenti cation,” a theme that appears throughout this manual For example, refer to
Experiments 3, 4, 37, 38, and 39 These experiments require good experimental niques that support an understanding of the chemical principles involved in the separa-tion and identi cation of the various compounds or ions Additionally, the amounts of
tech-a substtech-ance of interest tech-are tech-also determined in other experiments
Obtain a small (⬃50 cm3) sample of soil, add water, and lter Test the ltrate
with the silver nitrate test reagent Test a second soil sample directly with the
hydrochloric acid test reagent What are your conclusions?
Disposal: Discard the test solutions in the Waste Salts container
Disposal: Discard the test solutions in the Waste Salts container
56 Identification of a Compound: Chemical Properties
B Chemical Properties of
Unknown Compounds
The Next Step
A dropper pipet 20 drops is
⬃1 mL of solution.
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Trang 5Experiment 2 Prelaboratory Assignment
Identification of a Compound:
Chemical Properties
Date Lab Sec Name Desk No
1 Experimental Procedure, Part A.
a What is the criterion for clean glassware?
b What is the size and volume of a “small, clean test tube”?
2 Experimental Procedure, Part A.2 Describe the technique for testing the odor of a chemical.
3 Identify at least ve observations that are indicative of a chemical reaction.
4 Experimental Procedure, Part A.1 Referring to Appendix G for the substances listed here; underline those that are
soluble and circle those that are insoluble:
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Trang 65 Experimental Procedure, Part A The substances NaCl, Na2CO3, MgSO4, and NH4Cl, which are used for test solutions,are all soluble ionic compounds For each substance, indicate the ions present in its respective test solution.
NaCl:
Na2CO3:
MgSO4:
NH4Cl: _
6 Three colorless solutions in test tubes, with no labels, are in a test tube rack on the laboratory bench Lying beside the
test tubes are three labels: potassium iodide, KI; silver nitrate, AgNO3; and sodium sul de, Na2S You are to place thelabels on the test tubes using only the three solutions present Here are your tests:
• A portion of test tube 1 added to a portion of test tube 3 produces a yellow silver iodide precipitate
• A portion of test tube 1 added to a portion of test tube 2 produces a black silver sul de precipitate
a Your conclusions are:
Trang 7Experiment 2 Report Sheet
Identification of a Compound:
Chemical Properties
Date Lab Sec Name Desk No
A Chemical Properties of Known Compounds
1AgNO3(aq) _ _ _ _ _ _
2NaOH(aq) _ _ _ _ _ _
3HCl(aq) _ _ _ _ _ _Write formulas for the precipitates that formed in Part A (See Appendix G)
Part A.1 _ _ _ _ _ _Part A.2 _ _ _ _ _ _Part A.3 _ _ _ _ _ _Sample no of unknown for Part A.4
4Compound in unknown solution
B Chemical Properties of Unknown Compounds
5Reagent A _ _ _ _ _ _
6Reagent B _ _ _ _ _ _
7Reagent C _ _ _ _ _ _Sample no of unknown for Part B.4
Compound of unknown is the same as Solution No
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Trang 8Laboratory Questions
Circle the questions that have been assigned
1 Identify a chemical reagent used in this experiment that can be used to distinguish CaCl2 (soluble) from CaCO3(insoluble) What is the distinguishing observation?
2 What test reagent used in this experiment will distinguish a soluble Cl⫺salt from a soluble salt? What is the tinguishing observation?
dis-3 Predict what would be observed (and why) from an aqueous mixture for each of the following (all substances are
water soluble)
a potassium carbonate and hydrochloric acid
b zinc chloride and silver nitrate
c magnesium chloride and sodium hydroxide
d ammonium nitrate and sodium hydroxide
4 Three colorless solutions in test tubes, with no labels, are in a test tube rack on the laboratory bench Lying beside the
test tubes are three labels: silver nitrate, AgNO3; hydrochloric acid, HCl; and sodium carbonate, Na2CO3 You are toplace the labels on the test tubes using only the three solutions present Here is your analysis procedure:
• A portion of test tube 1 added to a portion of test tube 2 produces carbon dioxide gas, CO2
• A portion of test tube 2 added to a portion of test tube 3 produces a white silver carbonate precipitate
a On the basis of your observations how would you label the three test tubes?
b What would you expect to happen if a portion of test tube 1 is added to a portion of test tube 3?
5 For individual solutions of the cations Ag⫹, Ba2⫹, Mg2⫹, and Cu2⫹, the following experimental observations werecollected:
Cu2⫹ Blue ppt/deep blue soln with excess No change No change
aExample: When an aqueous solution of hydrochloric acid is added to a solution containing Ag ⫹ , a white precipitate (ppt) forms.
From these experimental observations,
a identify a reagent that distinguishes the chemical properties of Ag⫹ and Mg2⫹ What is the distinguishingobservation?
b identify a reagent that distinguishes the chemical properties of HCl and H2SO4 What is the distinguishingobservation?
c identify a reagent that distinguishes the chemical properties of Ba2⫹and Cu2⫹ What is the distinguishing tion?
observa-*d identify a reagent that distinguishes the chemical properties of Cu2⫹and Mg2⫹ What is the distinguishing vation?
obser-6 Three colorless solutions in test tubes, with no labels, are in a test tube rack on the laboratory bench Lying beside the
tests tubes are three labels: 0.10 M Na2CO3, 0.10 M HCl, and 0.10 M KOH You are to place the labels on the test
tubes using only the three solutions present Here are your tests:
• A few drops of the solution from test tube 1 added to a similar volume of the solution in test tube 2 produces no ible reaction but the solution becomes warm
vis-• A few drops of the solution from test tube 1 added to a similar volume of the solution in test tube 3 produces carbondioxide gas
Identify the labels for test tubes 1, 2, and 3
SO42⫺
60 Identification of a Compound: Chemical Properties
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Trang 9Experiment 25
Calorimetry
• To determine the speci c heat of a metal
• To determine the enthalpy of neutralization for a strong acid–strong base reaction
• To determine the enthalpy of solution for the dissolution of a saltThe following techniques are used in the Experimental Procedure:
Experiment 25 287
A set of nested coffee cups is a good constant pressure calorimeter.
Objectives
Techniques
Accompanying all chemical and physical changes is a transfer of heat (energy); heat may
be either evolved (exothermic) or absorbed (endothermic) A calorimeter is the
labora-tory apparatus that is used to measure the quantity and direction of heat ow ing a chemical or physical change The heat change in chemical reactions is quantitativelyexpressed as the enthalpy (or heat) of reaction, H, at constant pressure H values are
accompany-negative for exothermic reactions and positive for endothermic reactions
Three quantitative measurements of heat are detailed in this experiment: ments of the speci c heat of a metal, the heat change accompanying an acid–base reac-tion, and the heat change associated with the dissolution of a salt in water
measure-The energy (heat, expressed in joules, J) required to change the temperature of one
gram of a substance by 1C is the speci c heat1of that substance:
(25.1)
or, rearranging for energy,
(25.2)
T is the temperature change of the substance Although the speci c heat of a
sub-stance changes slightly with temperature, for our purposes, we assume it is constantover the temperature changes of this experiment
The speci c heat of a metal that does not react with water is determined by (1) ing a measured mass of the metal, M, to a known (higher) temperature; (2) placing it into
heat-a meheat-asured heat-amount of wheat-ater heat-at heat-a known (lower) temperheat-ature; heat-and (3) meheat-asuring the nheat-alequilibrium temperature of the system after the two are combined
energy (J) specific heat 冢 J
Specific Heat of a Metal
1 The specific list of a substance is an intensive property (independent of sample size), as are its ing point, boiling point, density, and so on.
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Trang 10The following equations, based on the law of conservation of energy, show the culations for determining the speci c heat of a metal Considering the direction of energy
ow by the conventional sign notation of energy loss being “negative” and energy gainbeing “positive,” then
(25.3)Substituting from equation 25.2,
(25.4)Rearranging equation 25.4 to solve for the speci c heat of the metalMgives
(25.5)
In the equation, the temperature change for either substance is de ned as the
differ-ence between the nal temperature, Tf, and the initial temperature, Ti, of the substance:
(25.6)These equations assume no heat loss to the calorimeter when the metal and thewater are combined The speci c heat of water is 4.18 J/g •C
The reaction of a strong acid with a strong base is an exothermic reaction that produceswater and heat as products
(25.7)The enthalpy (heat) of neutralization, Hn, is determined by (1) assuming the den-sity and the speci c heat for the acid and base solutions are equal to that of water and(2) measuring the temperature change, T (equation 25.6), when the two are mixed:
(25.8)
Hnis generally expressed in units of kJ/mol of water that forms from the
reac-tion The mass (grams) of the solution equals the combined masses of the acid and base
solutions
When a salt dissolves in water, energy is either absorbed or evolved, depending on themagnitude of the salt’s lattice energy and the hydration energy of its ions For the dis-solution of KI:
(25.9)The lattice energy (an endothermic quantity) of a salt, HLE, and the hydration
energy (an exothermic quantity), Hhyd, of its composite ions account for the amount ofheat evolved or absorbed when one mole of the salt dissolves in water The enthalpy
(heat) of solution, Hs, is the sum of these two terms (for KI, see Figure 25.1)
(25.10)Whereas HLEand Hhydare dif cult to measure in the laboratory, Hsis easilymeasured A temperature rise for the dissolution of a salt, indicating an exothermicprocess, means that the Hhydis greater than the HLEfor the salt; conversely, a tempera-ture decrease in the dissolution of the salt indicates that HLEis greater than Hhydand
K(aq) I (aq) Hs 13 kJ/mol
enthalpy change, Hn specific heatH 2 O combined massesacid base T
H3O(aq) OH (aq) l 2 H2O(l) heat
T Tf Ti
specific heatM specific heatH2 O massH 2 O TH 2 O
massM TM
specific heatM massM TM specific heatH 2 O massH 2 O TH 2 O
energy (J) lost by metalM energy (J) gained by waterH 2 O
Enthalpy (Heat) of Solution
for the Dissolution of a Salt
Enthalpy of neutralization: energy
released per mole of water formed
in an acid–base reaction—an
exothermic quantity
The negative sign in equation 25.8 is
a result of heat “loss” by the
acid–base reaction system.
Lattice energy: energy required to
vaporize one mole of salt into its
gaseous ions—an endothermic
quantity
Hydration energy: energy released
when one mole of a gaseous ion is
attracted to and surrounded by water
molecules forming one mole of
hydrated ion in aqueous solution—
an exothermic quantity
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Trang 11(25.12)Refer to equation 25.6 for an interpretation of T The speci c heats of some salts
are listed in Table 25.1
H s (specific heatH2 O massH 2 O TH 2 O) (specific heatsalt masssalt Tsalt)
Procedure Overview: Three different experiments are completed in a “double”
cof-fee cup calorimeter Each experiment requires careful mass, volume, and temperaturemeasurements before and after the mixing of the respective components Calculationsare based on an interpretation of plotted data
Ask your instructor which parts of this experiment you are to complete
You and a partner are to complete at least two trials for each part assigned Thetemperature versus time curves to be plotted in Parts A.5, B.4, and C.4 can beestablished by using a thermal probe that is connected directly to either a calculator or acomputer with the appropriate software If this thermal sensing and/or recordingapparatus is available in the laboratory, consult with your instructor for its use and adap-tation to the experiment The probe merely replaces the glass or digital thermometer inFigure 25.4, page 291
Experimental Procedure
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Trang 12Prepare a boiling water bath in a 400-mL beaker as shown in Figure 25.2.
1 Prepare the metal Obtain 10–30 g of an unknown dry metal2from your instructor.Record the number of the unknown metal on the Report Sheet Use weighing paper to
measure its mass on your assigned balance Transfer the metal to a dry, 200-mm testtube Place the 200-mm test tube in a 400-mL beaker lled with water well above thelevel of the metal sample in the test tube (Figure 25.2) Heat the water to boiling andmaintain this temperature for at least 5 minutes so that the metal reaches thermalequilibrium with the boiling water Proceed to Part A.2 while the water is heating
2 Prepare the water in the calorimeter The apparatus for the calorimetry
experi-ment appears in Figure 25.4 Obtain two 6- or 8-oz Styrofoam coffee cups, a tic lid, stirrer, and a 110 glass or digital thermometer Thoroughly clean theStyrofoam cups with several rinses of deionized water Measure and record the com-bined mass (0.01 g) of the calorimeter (the two Styrofoam cups, the plastic lid,and the stirrer)
plas-Using a graduated cylinder, add ⬃20.0 mL of water and measure the mass of
the calorimeter plus water Secure the glass or digital (Figure 25.3) thermometer
with a clamp and position the bulb or thermal sensor below the water surface.(Caution: Carefully handle a glass thermometer If the thermometer is acciden-
tally broken, notify your instructor immediately.)
3 Measure and record the temperatures of the metal and water Once thermal
equilibrium has been reached in Parts A.1 and A.2, measure and record the
temper-atures of the boiling water from Part A.1 and the water in the calorimeter from Part A.2 Record the temperatures using all certain digits plus one uncertain digit.
4 Transfer the hot metal to the cool water and record the data Remove the test
tube from the boiling water and quickly transfer only the metal to the water in the
calorimeter.3Replace the lid and swirl the contents gently Record the water perature as a function of time (about 5-second intervals for 1 minute and then15-second intervals for ⬃5 minutes) on the table at the end of the Report Sheet.
tem-290 Calorimetry
A Specific Heat of a Metal
2 Ask your instructor to determine the approximate mass of metal to use for the experiment.
3 Be careful not to splash out any of the water in the calorimeter If you do, you will need to repeat the entire procedure Also, be sure that the metal is fully submerged in the calorimeter.
The temperature is to be recorded
with the correct number of significant
figures.
Use a stirring rod to assist in the
gentle transfer of the metal into
the water of the calorimeter.
Temperature probe 200-mm test tube
Metal only Water level 400-mL beaker
Gentle heat
to boiling
Figure 25.2 Placement of the metal in
the dry test tube below the water surface
in the beaker A Bunsen flame may replace the hot plate.
Figure 25.3 A modern digital
thermometer can be substituted for a glass thermometer.
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Trang 135 Plot the data Plot the temperature (y-axis) versus time (x-axis) on the top half of
a sheet of linear graph paper or by using appropriate software The maximum perature is the intersection point of two lines: (1) the best line drawn through thedata points on the cooling portion of the curve and (2) a line drawn perpendicular
tem-to the time axis at the mixing time [when the metal is added tem-to the water (Figure25.5)].4Have your instructor approve your graph
6 Do it again Repeat Parts A.1 through A.5 for the same dry metal sample Plot the
data on the bottom half of the same sheet of linear graph paper
Obtain 110 mL of 1.1 M HCl, 110 mL of 1.1 M HNO3and 210 mL of standardized
1.0 M NaOH from the stock reagents.
1 Measure the volume and temperature of the HCl Measure 50.0 mL of 1.1 M
HCl in a clean graduated cylinder Measure and record its temperature.
2 Measure the volume and temperature of the NaOH Using a second clean
graduated cylinder, transfer 50.0 mL of a standard 1.0 M NaOH solution to the
dry calorimeter (see Figure 25.4) Record the temperature and exact molar tration of the NaOH solution
concen-3 Collect the data Carefully but quickly add the acid to the base, replace the
calorimeter lid, and swirl gently Read and record the temperature and time every
5 seconds for 1 minute and thereafter every 15 seconds for ⬃5 minutes
4 Plot the data Plot the temperature (y-axis) versus time (x-axis) on the top half of a
sheet of linear graph paper or by using appropriate software Determine the mum temperature as was done in Part A.5 Have your instructor approve your graph
maxi-5 Do it again Repeat the acid–base experiment, Parts B.1 through B.4 Plot the data
on the bottom half of the same sheet of graph paper
Disposal: Return the metal to the appropriately labeled container, as advised
by your instructor
Experiment 25 291
Appendix C
Figure 25.4 Schematic of a “coffee
cup” calorimeter (see opening photo)
4 The maximum temperature is never recorded because of some, albeit very small, heat loss to the calorimeter wall.
Figure 25.5 Extrapolation of temperature versus time data (not to
scale) for an exothermic process
B Enthalpy (Heat)
of Neutralization for an Acid–Base Reaction
Standard solution: a solution with a very accurately measured
concentration of a solute
Appendix C
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Trang 146 Change the acid and repeat the neutralization reaction Repeat Parts B.1
through B.5, substituting 1.1 M HNO3for 1.1 M HCl On the Report Sheet,
com-pare the Hnvalues for the two strong acid–strong base reactions
Measure the mass of salt for each of the separate trials (Part C.5) while occupying thebalance
1 Prepare the salt On weighing paper, measure about 5.0 g (⫾0.001 g) of the
assigned salt Record the name of the salt and its mass on the Report Sheet.
2 Prepare the calorimeter Measure the mass of the dry calorimeter Using your
clean graduated cylinder, add ⬃20.0 mL of deionized water to the calorimeter.Measure the combined mass of the calorimeter and water Secure the thermometerwith a clamp and position the bulb or thermal sensor below the water surface (seeFigure 25.4) and record its temperature
3 Collect the temperature data Carefully add (do not spill) the salt to the
calorimeter, replace the lid, and swirl gently Read and record the temperatureand time at 5-second intervals for 1 minute and thereafter every 15 seconds for
⬃5 minutes
4 Plot the data Plot the temperature (y-axis) versus time (x-axis) on the top half of
a sheet of linear graph paper or by using appropriate software Determine themaximum (for an exothermic process) or minimum (for an endothermic process)temperature as was done in Part A.5 Have your instructor approve your graph
5 Do it again With a fresh sample, repeat the dissolution of your assigned salt,
Parts C.1 through C.4 Plot the data on the bottom half of the same sheet of lineargraph paper
CLEANUP: Rinse the coffee cups twice with tap water and twice with deionized
water, insert the thermometer into its carrying case, and return them
Heat is evolved or absorbed in all chemical reactions (1) Since heat is transferredto/from the calorimeter, design an experiment to determine the calorimeter constant
(called its heat capacity) for a calorimeter (2) An analysis of the combustion of
differ-ent fuels is an interesting yet challenging project Design an apparatus and develop aprocedure for the thermal analysis (kilojoules/gram) of various combustible materials—for example, alcohol, gasoline, coal, or wood
Disposal: Discard the salt solution into the Waste Salts container, followed byadditional tap water Consult with your instructor
Disposal: Discard the neutralized solutions contained in the calorimeter into theWaste Acids container Rinse the calorimeter twice with deionized water
the heat lost to or gained by the
calorimeter per degree Celsius
temperature change.
energy change
C
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