Inorganic lab manual

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CHEMISTRY 323 Inorganic Chemistry LABORATORY MANUAL

Department of Chemistry

Tulane University

Fall 1997

TABLE OF CONTENTS

Page

Schedule of Experiments ii

Safety Regulations 1Inorganic Laboratory Course 3

Influence of Ligand Field Tetragonality on the Ground State Spin of

Nickel (II) Complexes 22

SCHEDULE OF EXPERIMENTS

September 24-30 Experiment 1 Section 3 and 4

Experiment 2 Section 2 and 3

Marking; All laboratory reports are due two weeks after the end

of the experiment Late reports will be penalized 5% per dayexcept in extenuating circumstances Each report will be worth10% of your final mark, with the lowest grade being dropped inthe final calculation The final exam will be worth 20% of thegrade

UNDERGRADUATE TEACHING LABORATORY SAFETY REGULATIONS

1 NO STUDENT MAY WORK IN A LABORATORY UNLESS AN INSTRUCTOR IS

ON DUTY

2 RECOMMENDED EYE PROTECTION MUST BE WORN AT ALL TIMES IN THELABORATORY, UNLESS SPECIFICALLY INSTRUCTED OTHERWISE.*

3 NO SMOKING, EATING OR DRINKING IS PERMITTED

4 LABORATORY COATS ARE RECOMMENDED WHILE WORKING IN THELABORATORY

* Regular prescription glasses are an adequate substitute only in the absence of an

explosion hazard or where no hazardous chemicals are being used in the laboratory.

In addition to these four basic rules, the following regulations should be observed:

1 No student may perform an unauthorized experiment

2 Never leave an experiment in progress unattended

3 Any chemical which produces toxic vapors must be used in a fumehood

4 Wipe-up spilled chemicals and bottle `rings' immediately

5 Never handle or pour flammable liquids near an open flame

6 Report all accidents to the instructor immediately

7 Unless given specific permission to the contrary, NEVER pipette a liquid by mouth; Use arubber bulb

8 Keep the sinks clean

9 At the end of the period, make sure the hood, work area and sink are clean and tidy

Suggestions

Learn the locations of the emergency shower, eyewash and fire extinguisher and know how

to use them While working in the laboratory, beware of burns from forgotten, still-lit burnersand from hot glassware Wash your hands at the end of each laboratory class

If you are unsure about any directions, ask your instructor For example, ask for his/herinstructions when disposing of used chemicals Finally, never hurry when performingexperiments Safety always has the highest priority

WORKPLACE HAZARDOUS MATERIALS INFORMATION SYSTEMS (WHIMS)

WHIMS provides that, by law, students are entitled to information concerning any materials used in the laboratory This material is available

on a Material Safety Data Sheet (MSDS) These are available from Tulane's Office of Environmental Health and Safety.

CHEMISTRY INORGANIC LABORATORY COURSE:

The experiments contained in this laboratory manual have ben designed to contribute tothe student's understanding of the principles of inorganic chemistry through:

1) The use of some of the modern techniques for the synthesis and investigation of

inorganic compounds

and 2) The gaining of first hand experience of inorganic compounds Note that the

experiments are not in some cases specifically tied to particular sections of thelecture course, but rather designed to augment the lectures in order to provide

a broad introductory course in inorganic chemistry

LABORATORY REPORTS

The format of the written laboratory report will vary slightly from experiment toexperiment, but in general thy are expected to contain the following:

(a) Purpose: Briefly describe what you plan to do, and why

(b) Procedure: Give a condensed version of what is in the manual Include the

exact weights of reagents/products you measured

(c) Observations: Describe what happened in your reaction, in some detail.(d) Analysis: If required, report the qualitative tests in the usual way

(Test/Observation/Inference) Include any spectra you recordedand provide interpretations where possible

(e) Discussion: Give an explanation of the steps in the synthesis, and of the

observations you made Give balanced chemical equationswherever possible Explain any anomalous (i.e too low, or toohigh) yields from syntheses

(f) Conclusion: Give a very brief summary of your results This will obviously

differ greatly from experiment to experiment

(g) Post-lab questions Answer fully all questions posed at the end of the laboratory

write-up

(h)References Include all references used in the laboratory write-up

Laboratory reports should be written in third person All reports must be typed or legiblyhandwritten Graphical representation of data should be computer generated.

The laboratory reports will be graded on the basis of 100 points, distributed as follows

EXPERIMENT 1

SYNTHESIS OF A SOLID ACID,

12-Tungstosilicic acid, H4SiW12O40@@ 7H2O

REFERENCES:

a) E North, Inorg Syntheses, 1, 129 (1939).

b) N N Greenwood and A Earnshaw, "Chemistry of the Elements" Pergamon Press, 1984,

pp 1171-1186

c) F A Cotton and G Wilkinson, Advanced Inorganic Chemistry, 5th Edition, pp 811-818.

d) D M Adams and J B Raynor, Advanced Practical Inorganic Chemistry

1 INTRODUCTION

The condensation of oxometalate anions in acidic solutions is a commonly encounteredreaction in inorganic chemistry For example, the following equilibria between molybdenumspecies are highly dependent on pH:

7[MoO4]2- + 8H+ X [Mo7O24]6- + 4H2O8[MoO4]2- + 12H+ X [Mo8O26]4- + 6H2OThese ions are only two of the many complex species which occur in solution, and hydration,protonation and further condensation or hydrolysis reactions can increase the diversity of thesesystems The basic building block of these isopolyanions is the MoO6 octahedron, and theseunits can be connected by sharing corners, edges, but not faces In some structures MoO4tetrahedra can also be found Tungsten exhibits very similar chemistry in this regard.There has been renewed interest in these types of compounds, largely as a result of theirpotential and actual, use as catalysts They have found use in selective oxidation and acidcatalyzed reactions

— Experiment 1 —

In this laboratory exercise you will prepare a heteropolymetalate species which is a solidacid The object of the experiment is to:

a) Prepare the compound 12-tungstosilicic acid using a solvent extraction method

b) Quantitatively determine the available protons in this material

C) To test the material as a solid acid catalyst

it, add a further 5 mL of concentrated hydrochloric acid slowly, and transfer it into aseparatory funnel Shake the solution with diethyl ether (12 mL); at this point you shouldobserve three layers in the funnel If not, add a little more ether, shake and again allow toseparate Withdraw the bottom, oily ether layer and save it in a beaker Repeat the extractionprocess several times, until the yellow product in the middle layer has been completelyremoved Discard the liquid left in the funnel (put it in the residues bottle), rinse out thefunnel, and return the ether extracts to the funnel, together with a solution of 4 mL ofconcentrated hydrochloric acid in 12 mL of water, and an additional 4 mL of ether Aftershaking, run off the lower (ether) layer into an evaporating dish and allow the solvent toevaporate Dry the white crystalline product at 70o C for about two hours, then put it into atared sample vial, reweigh the vial and record your yield

DO NOT USE A METAL SPATULA TO HANDLE YOUR PRODUCT, OR IT WILL TURN BLUE!

3 Determination of the acidity of the product

Weigh out about four grams of the product and dissolve it in deionized water, and dilute

to 100 mL in a volumetric flask Titrate 40 mL aliquots of the solution with the 0.1 M NaOHsolution provided, using an appropriate indicator (e.g methyl orange or chlorophenol red).Assuming the formula given in the title, calculate the moles of titratable protons per mole ofcompound

4 Test of H4SiW12O40@ XH2O as a Solid Acid

Add 6 drops of cyclohexanol to 3 mL of cyclohexane Shake to dissolve Add ca O.2 g of

H4SiW12O40 and shake for a few minutes Filter to remove the solid acid from the solution A.Prepare a second solution B of 6 drops of cyclohexanol in 3 mL of cyclohexane Add ca 10drops of dilute bromine water (pale brown color) - 20 drops of saturated Br2 water in 20 mls ofdistilled water - to each of the cyclohexane solutions and shake Solution A should decolor, and

a white precipitate of C6H10Br2 may appear in the organic layer

Solution B will extract the brown Br2 out of the Br2 water into the organic layer, but theorganic layer will not decolor

NB: It is important to filter out the solid acid after reaction with cyclohexanol since it

appears to react with bromine water by itself

3 What other atoms can occupy the tetrahedral position in the center of the M12 polyanion

in which the Si is found in H4SiW12O40@ 7H2O ?

Drying tubeMossy tin

Chlorosulfonicacid

Apparatus for the Synthesis of Tin(IV) Chloride

EXPERIMENT 2

TIN(IV) HALIDES

1 Introduction

Read the appropriate section of F A Cotton and G Wilkinson, Advanced Inorganic

Chemistry, 5th Edition in order to acquire some background for interpretation of the

observations in Part 4 of this experiment

2 Preparation of Tin(IV) Chloride

L [CAUTION: ClSO3 H REACTS VIOLENTLY WITH WATER.]

Because the handling of reagents used in this experiment could be hazardous, consult your

instructor before beginning You MUST use a fumehood, and keep the window between you

and the experiment It is important that the apparatus you use is properly dried before youstart

Put 5.5 g of mossy tin into a 25 ml semi-micro distillation flask and slowly add 13 ml ofClSO3H (chlorosulfonic acid) from a tap funnel The addition should be just fast enough tomaintain a steady reaction, and to provide enough heat to distil the stannic chloride into thereceiving flask When the reaction is complete, redistill the product, if necessary It should be

a colorless liquid, b p - 110o C

Sn + 4ClSO3H xv SnCl4 + 2SO2 + 2H2SO4

N B SnCl4 + 2H2O xv SnO2 + 4HCl

As soon as the product is obtained, stopper it in a flask

3 Preparation of Tin(IV) Iodide

Weigh 1.0 g of granulated tin and 3.3 g of iodine into a 25 ml flask Add 15 ml of carbontetrachloride and one or two small boiling chips and fit a reflux condenser to the flask Warmthe flask gently, using a water bath on a hot plate, until the reaction starts and then removethe source of heat

Re-apply heat as necessary to maintain a steady refluxing of the solvent until no free iodineremains (Solution is orange-red instead of violet.)

Remove the condenser, heat the solution to boiling point and filter through a fluted filterpaper to remove excess tin The filtering equipment should be preheated with hot solvent inorder to prevent the product from crystallizing prematurely Wash the residue in the flask and

on the filter with 3 ml of hot carbon tetrachloride, combining the washings with the mainfiltrate

Cool the solution in an ice bath and filter off the solid Evaporate the filtrate to about bulk to obtain a further crop of crystals Weigh and record the yield Calculate the theoreticalyield (based on iodine)

half-The solid may be recrystallized from carbon tetrachloride

4 Reactions of Tin(IV) Halides

hydrochloric acid, (v) 2M-sodium hydroxide solution Note color of solutions, possiblereactions, and write equations to explain all observations.

(b) Stability to oxidation, e.g acidic permanganate solution.

(c) Stability to reduction, e.g acidic stannous chloride, zinc metal and dilute hydrochloric

acid

(d) Complexation, or "adduct"-forming reactions To a solution of 2.0 g triphenyl phosphine in

2 ml benzene, add a solution of 0.5 g of SnCl4 in 2 ml benzene Repeat this reaction with0.5 g SnI4 How does the reactivity of SnCl4 change as a result of forming a complex with

EXPERIMENT 3

REDOX CHEMISTRY OF CHROMIUM

1 Preliminary Exercises

Consult F A Cotton and G Wilkinson, Advanced Inorganic Chemistry, 5th Edition for a

list of the oxidation states of chromium

2 Reactions with Hydrogen Peroxide

Carry out the following tests Record your observations and explain them on the basis ofthe information gleaned from the preliminary exercises

(a) Dissolve 25 mg of chromium(III) sulfate in 2 ml of water Divide the solution into

2 parts To one add 1 ml 2M-sulfuric acid, to the other add 1 ml 2M sodiumhydroxide solution Then to each add 1 ml hydrogen peroxide (6% solution) Afterobserving any initial reaction warm the solution

(b) Dissolve 25 mg of potassium chromate in 2 ml of water Divide the solution into 2 partsand repeat the test described in (a)

3 Preparation of Chromium(II) Acetate

Chromous acetate as a dimeric, relatively insoluble material is a relatively stablechromium(II) compound, the rate of oxidation being sufficiently slow to enable it to be preparedwithout the elaborate precautions of oxygen, which other chromous preparations demand.Each chromium ion in the dimer has six octahedral bonds, four to the oxygen atoms of theacetate groups (which act as bridging ligands between the two chromium ions), one to a watermolecule and the sixth a mutual chromium-chromium bond

30 minutes Allow to cool.

During this time assemble the apparatus shown in the diagram below:

Add a similar quantity of carbon dioxide to a 400 ml beaker containing 300 ml of water.Cover this beaker with a watchglass, and add more carbon dioxide as required to maintain an

Allow the reaction in A to continue until the solution has a clear sky-blue color Then close

C so that the solution is forced through E and H into J The chromous acetate precipitatesimmediately as a red-brown solid

The product needs to be protected from oxygen while you are working it up A simple way

is to add a few small pieces of dry ice to the Büchner funnel in which you are filtering off theprecipitate This will generate an atmosphere of CO2 over the solution, and the sample Afterfiltering off the solid wash it with oxygen free water, then finally with acetone Dry theproduct in a vacuum desiccator

5 Analysis of the Chromium(II) Compound

The chromium content is determined by conversion to CrO42-, and the measurement of theintensity of the yellow color using the spectrophotometer

A weighed sample of the compound** is dissolved in dilute nitric acid to give a solution ofvarious CrIII ions Make the solution up to 100 ml in a volumetric flask, take a 5.0 ml aliquotand place it in a 250 ml Erlenmeyer flask Add enough 2.0 M NaOH to neutralize the free acid,and then add 10.0 ml more NaOH Add about 5-10 drops of 30% hydrogen peroxide, then heat

on a steambath for a few minutes until oxygen evolution ceases Cool to room temperature andmake up to 250 ml A duplicate determination should be made, and also in this case a blank

solution (same reagents and procedure but no Cr).

Measure the absorbance of both solutions and blank in a 1 cm path length cell at 374 nmand calculate the concentration of chromate ion from the relationship:

— Experiment 3 —

CR

0 = molar extinction coefficient = 4820 L mol-1 cm-1 at 374 nm

A = absorbance - measured by experiment

c = molar concentration - calculated from measured value of A

R = path length of cell - 1 cm

Remember the dilution step when calculating chromium content of the original sample

(b) The book Synthesis and Technique in Inorganic Chemistry by R J Angelici has some

useful information on this experiment

2 Preparation of Tetraaminecarbonatocobalt(III) Nitrate

[Co(NH3)4CO3]NO3

Dissolve 20 g of ammonium carbonate in 60 ml of water and add 60 ml concentratedaqueous NH3 (solution A) Dissolve 15 g of cobalt(II) nitrate hexahydrate in 30 ml of water(solution B) Mix solution A with solution B and add 8.0 ml of 30% hydrogen peroxide solution(slowly), stirring continuously Pour this solution into an evaporating dish and concentrate toabout 90 ml on a hot plate During the evaporation add in small portions, a total of 5 g ofammonium carbonate Filter the hot solution and cool the filtrate in an ice-water bath Whencrystallization is complete, filter off the red crystals under suction, and wash with 2-3 ml ofwater then two or three times with 10 ml of ethanol Preserve some sample for conductance