Chemistry 323: Main Group Chemistry Lab Manual

Introduction Safety in the Undergraduate Teaching Laboratories Laboratory Procedures Research Notebooks Laboratory Reports Grading Scheme Order of Experiments

ii iv v vi vi vii

Note: Students are to perform all experiments (within each group there may be some choice). Students will work in pairs, but must submit separate reports and keep separate lab books. Group 13 Part 1: Synthesis of an aluminum coordination complex, aluminum acetylacetonate, Al(C5H7O2)3. Part 2: Synthesis of a covalent boron compound (pick 1 of two) Group 14 Part 1: Silicone polymers Part 2: Transformation of lead compounds Group 15 Part 1: Synthesis and complexation of diphos Part 2: Synthesis of Group 15-based complex ions Group 16 Part 1: Synthesis of Potassium Peroxydisulfate Part 2: Synthesis of a Heavy Chalcogen Compound (pick 1 of 3) Group 17 Part 1: Synthesis of a polyhalogen anion containing iodine (pick 1 of 2) Part 2: Analysis of iodine content by redox titration

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ii INTRODUCTION This course is designed to introduce the student to research techniques in inorganic chemistry. The experiments to be carried out involve the synthesis of various types of compounds by diverse experimental techniques. Instrumental methods will be used to characterize the products. The entrance into these new areas of research requires a greater appreciation of safety hazards related not only to the chemical properties of reactants but also to the dangers presented by unfamiliar apparatuses. New fundamental techniques will be encountered, and these must become as second nature as weighing and pipetting were in prior courses. Finally, the research orientation of the course requires careful record-keeping by the researcher. This first chapter will expand upon certain aspects of (1) safety, (2) basic laboratory procedures, and (3) methods of keeping a research notebook. It is important that you become well acquainted with this material before beginning the experiments. SAFETY IN THE UNDERGRADUATE TEACHING LABORATORIES These notes are directed to all users of undergraduate chemistry teaching laboratories. General Guidelines for Safety 1.

No undergraduate may perform an experiment to which the student has not been specifically assigned. Other than in project courses, no undergraduate experiment of any kind may be performed in the absence of an instructor, demonstrator or technician.

2.

Learn the location of escape routes and of all safety equipment (showers, eye wash station, fire extinguishers, fire alarm, telephone, etc.) before you start to work in any room. Know how to use the equipment.

3.

Smoking, eating or drinking is not permitted. Nothing should be placed in the mouth. Pipetting by mouth is absolutely forbidden.

4.

Regard all chemicals as potentially hazardous. Treat with special caution those chemicals that the laboratory manual cites as toxic, poisonous or otherwise dangerous. Do not attempt to clean up any spills yourself - inform the demonstrator of the problem as soon as possible.

5.

Compressed gas cylinders should always be securely anchored to a wall or heavy bench. If a large cylinder tips over and the valve snaps off, the cylinder becomes a jet-propelled missile which has sufficient power to penetrate a brick laboratory wall.

6.

If you are in doubt as to the safety of a procedure, don't do it until you have sought professional advice.

7.

All accidents, however minor, must be reported to the person in charge of the lab section immediately.

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Practice good housekeeping - a clean work space is much safer than a messy one. The dangers of spilled acids and chemicals and broken glassware created by thoughtless actions are too great to be tolerated. Clean up your work space, including wiping the surface and putting away all chemicals and equipment, at the end of the laboratory period.

Some Additional Good Practice Rules 1.

Carefully read the experiment before coming to the laboratory. An unprepared student is a hazard to everyone in the room.

2.

Dispose of excess reagents as directed by your instructor or laboratory demonstrator. Never return reagent to bottles.

3.

Always pour acids into water when mixing. Otherwise the acid can spatter, often quite violently.

4.

Avoid breathing fumes of any kind. (a) To test the smell of a vapour, collect some in a cupped hand. (b) Work in a hood if there is the possibility that noxious or poisonous vapours may be produced.

5.

Be careful when heating liquids. Flammable liquids such as ethers, hydrocarbons, alcohols, acetone, and carbon disulfide must never be heated over an open flame.

6.

Test tubes being heated or containing reacting mixtures should never be pointed at anyone. If you observe this practice in a neighbour speak to them or the instructor.

7.

Do not force rubber stoppers onto glass tubing or thermometers. Lubricate the tubing and the stopper with glycerol or water.

8.

Finally, and most importantly, THINK about what you’re doing. Plan ahead. If you give no thought to what you are doing, you predispose yourself to an accident.

Personal Protective Equipment 1.

Eye protection must be worn at all times in the undergraduate teaching labs. Adequate eye protection consists of impact resistant safety glasses or goggles which have side shields and a top flange in contact with the forehead. People who normally wear prescription glasses will be required to purchase detachable side shields to be worn in the lab. If the prescription glasses are deemed to be inadequate for satisfactory eye protection (due to small lens size), safety glasses or goggles which can be worn over the prescription glasses will be required.

2.

Contact lenses MUST NOT be worn into a chemistry lab under any circumstances.

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Adequate footwear which fully covers the feet must be worn. Sandals and open-toed shoes are not acceptable. Wearing high heels or shoes with no treads is discouraged.

4.

Lab coats are required when working in the chemistry labs to prevent exposure to corrosive or otherwise harmful chemicals. Lab coats should not be worn outside of the labs, especially in areas where food is prepared or consumed, since they could contaminate areas not normally exposed to chemicals.

5.

Long hair and bangs must be tied back. LABORATORY PROCEDURES

Use of time Plan your experiments so that you will profitably use time that would otherwise be spent watching, e.g., a distillation, a sublimination, or a nonhazardous reaction that need not be attended. This course allows some latitude in the planning of experiments, and you should be looking for opportunities to use the available time effectively. Cleanliness Since most of the experiments will involve the use of equipment that other students will use sometime during the course, it is essential that all equipment be left in good condition at the end of each period. Any equipment that is broken should be reported to the instructor immediately so that a replacement may be found in time for the next class. Glassware that is difficult to clean with a detergent are more conveniently cleaned by pouring a few milliliters of concentrated H2SO4 into the soiled flask, followed by an equal volume of 30 per cent H2O2 and then by swirling the mixture. This is a very strong oxidizing mixture, which rapidly cleans almost any glassware. Needless to say, the H2SO4-H2O2 solution dissolves clothing and produces severe skin burns; it should be handled with rubber or polyethylene gloves. Performance of experiments The laboratory programme is a very important component of the Chemistry 322 course and it is imperative that students be well prepared prior to coming into the laboratory. Many experiments will require more than one week to complete and it will be necessary to find appropriate places in the procedures where experiments can be left safely until the next laboratory period. Experiments should be signed out a week in advance on the sheet provided in the laboratory. Note that it will be necessary to check the sign-up sheet to find out which experiments will be available. Some experiments may require the student to come in outside the lab time for a brief period. Those will be set up on an appointment basis agreeable to both the student and the lab instructor.

v Often times, in a research laboratory, quality is more important than quantity. For this reason, students are expected to show their products to the demonstrator for inspection. As many of these products are air sensitive, the sooner after isolation it is seen, the better. Additionally, some labs call for recystallisation of the product. A trick that has saved numerous students is to set aside a small portion of the unrecrystallised product in case this step goes awry. Occasionally, recrystallisation actually give an inferior looking product! Except in exceptional circumstances (e.g., illness), attendance at the laboratory sessions is mandatory (until all experiments are completed). RESEARCH NOTEBOOK The communication of scientific facts and experimental results is an important duty of the scientist. Without it, little would be gained from the scientist's efforts. The first step in the communication chain is the accurate and detailed recording of experimental facts in a bound notebook. The purpose of this record is to allow you or someone else to learn from what you did in the experiment and to help you or them to repeat your success or avoid your failure. Detailed information about a synthesis or measurement is much appreciated by someone wishing to repeat your experiment. Your notebook records of your experiments should include more than enough detail to allow you or someone else to repeat the experiment successfully. It is much better to be overly detailed than to overlook observations that may be of use later. Your notebook may contain drawings of experimental apparatus (or a reference to a figure in this manual). It should also contain experimental observations such as colour changes, temperatures of reaction mixtures, difficulties encountered, weighings, measurements, and cross references to spectra (label spectra with notebook page number on which the compound preparation is given). All of these experimental details should be recorded in the notebook at the time of the observation. Data are not to be first written on loose paper. This rule was not instituted by a cranky teacher; it is simply a waste of time to record observations and then recopy them into a notebook. Needless to say, if this rule is followed, your research notebook will not be a work of art in neatness, but it should be readable. Since water and acid may spill on the notebook, it is important that your records be kept with permanent ink. Mistakes are simply crossed out. Information specifically requested at the end of each experiment should also be included at the end of the experimental observations. Each page of the notebook should be numbered and dated to indicate the day that the experiment was performed. To facilitate referring to experiments, the first two or three pages in the notebook should be left blank for a table of contents. As you complete an experiment, its title and page should be recorded in this table of contents. Your grade for the notebook will be based on completeness of experimental information, as well as point-form answers to any experiment questions which you did not answer in a formal report.

vi LABORATORY REPORTS The lab due dates are listed on the class calendar, which will be handed out in class. Each person is responsible for 2 formal reports. The writeups should follow the general form of a journal article. As such, the following sections should be used: Abstract – this is a specific statement of the nature of the experiment, stating what was learned in a succinct manner. It should be no longer than 5-8 lines. Introduction – this is a general introduction, which would include background theory. Experimental – this should be in journal form, which assumes the reader has a fundamental knowledge of equipment and techniques (e.g., the term “distillation” need not be defined, and a distillation aparatus should not be drawn in the formal report). Therefore, it can be quite brief, but must give all necessary information (masses, melting points, observed spectral lines in IR, etc.). This could also go at the end (immediately before the references) of the paper. Results and Discussion – this is the bulk of the paper, and can be divided up into subsections as required. For example, there is often a section titled “synthesis,” which can expand on the information in the experimental section. This is normally where explanations of unusual techniques, sources of experimental error, etc. would be discussed. Any questions that are to be answered as listed in the lab manual would generally go in this section (or the intro) – these should be worked into the discussion and not written in point form. References – all literature material must be referenced. They can either be reported as footnotes or endnotes. The labs will be marked out of 20 points, with the following breakdown: Abstract: 2 points Intro/Discussion (including answers to the questions): 10 points Experimental: 4 points Overall presentation (including references, grammer, etc.): 4 points GRADING SCHEME The lab is worth 25% of the total mark in the course. While the information in the labs will not be specifically tested on exams, the underlying theory ties in with the course work. 20% 5%

formal lab reports (two, 10% each) research notebook, including answers to all discussion questions not formally reported.

NOTE: Although the experiments will be done in pairs, each student must submit their own formal reports and lab book. It is expected that these reports will be done independently. ORDER OF EXPERIMENTS These experiments do not directly follow the course material, but are instead designed to give a

vii flavour of experimental techniques. As such, the experiments can be done in any order. There will be a sign-up sheet in the lab. Since there is a limited number of sets of apparatus, you will have to book the week before. In addition, this booking system will ensure that all the chemicals and glassware you need will be available at the start of the laboratory period. The experimental groups represent the groups on the periodic table. Some groups have choice, while others do not. Compounds of the Nobel Gases are highly explosive and usually require highly specialised equipment to synthesise (i.e., stainless steel reactor vessels, very high pressures, etc.), so we will not be making such compounds in this course. In addition, the s-block elements will not be specifically investigated, but are normally present as cations in many of the compounds that will be synthesised, and thus will be studied incidentally.

The Chemistry of Group 13 Boron is the only true non-metal in Group 13. Aluminum is often considered a metalloid, but has most of the classical characteristics of a metal (conductivity, maleability, lustre). The heavier elements are undoubtedly metals (gallium through thallium), but they have some significant differences to the transition metals, most noticably the stability (in In and Tl) of the +1 oxidation state. The lighter metals (Ga and Al) invariably exist in the +3 oxidation state. Boron, on the other hand, has access to both the +3 and the -1 formal oxidation states, although these are normally in covalent compounds, not ionic. The most obvious characteristic of the lighter Group 13 elements is the low valency - neutral compounds would contain only 3 bonds to the Group 13 element. Thus, most simple, binary compounds of this group are Lewis acids, seeking to fulfill an octet about the central atom by binding to an electron pair of a Lewis base. In the case of boron, this has led to a very rich and diverse cluster chemistry. Aluminum and galluim can often form simple anions such as AlF4- and GaCl4-, and also some hypervalent or more complex ions such as AlF63- and Ga2Cl7-. In this experiment, you will synthesise an aluminum coordination compound and a covalent (molecular) boron compound, to emphasise the difference in reactivity between B and Al. The heavier elements of Group 13 are either too expensive (Ga) or highly toxic (In, Tl), and will not be used in this laboratory.

Part 1. Synthesis of an aluminum coordination complex, aluminum acetylacetonate, Al(C5H7O2)3. Preamble: Acetylacetonate, commonly abbreciated “acac,” is one of the most common inorganic ligands. Acetylacetone has one acidic proton, which is removed on addition of base to give the monoanionic acac ligand, C5H7O2-. In this synthesis, you will demonstrate the metallic properties of aluminum by synthesising a classic coordination complex. To 20 mL of water, add 3.0 g of acetylacetone. This will form a bilayer. Add 6 N NH3 solution dropwise (hood), with swirling, until the acetylacetone dissolves (this forms acac). This solution is added to a solution of 3.0 g of aluminum sulfate heptadecahydrate, Al2(SO4)3.17H2O, in 30 mL of water. The product should precipitate immediately from the neutral (pH 7) solution. Suction filter the crude product, washing with water. Dissolve the crude material in toluene, and reprecipitate with addition of petroleum ether. Suction filter and wash with pet. ether. Check the purity of your product by taking its melting point.

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Questions: 1. Draw the structure of acetylacetone and point out the most acidic hydrogen. 2. Report your melting point and compare with the literature value. 3. Suggest a method to further purify the product. Reference: Young, R.C. Inorg. Synth. 1946, 2, 25.

Part 2. Synthesis of a Boron Compound In this part of the experiment, you will synthesise a molecular compound containing boron. Do either Part A or Part B. Part A. Synthesis of 1,3-dimethyl-1,3-diaza-2-boracyclopentane Preamble: N,N’-dimethylethylenediamine is also a ligand for the formation of metal complexes. When reacted with boron compounds, however, the result is a covalent bond between N and B. Synthesis: Set up a 2-neck 100 mL round-bottomed flask with a reflux condenser attached to one neck (hood). Attach a drying tube to the top of the condenser, and a nitrogen line to the other neck of the rbf. Dry the apparatus by heating with a bunson burner (with N2 flowing through the system). While continuing to pass N2 gas, add 3.6 g of trimethylamine-borane adduct, 4.3 g of N,N’-dimethylethylenediamine, and a few boiling chips. Reflux for the rest of the lab period (at least 2 hours). Store the crude material in a sealed vessel under nitrogen In the next lab period, flame dry a distillation apparatus and attach a drying tube (hood). Under a static pressure of N2, distill the oil (around 90°C). Run an infrared spectrum on the resultant oil to check the purity. Questions: 1. Draw the structure of 1,3-dimethyl-1,3-diaza-2-boracyclopentane. Are there any possible resonance structures wherein the octet of B is satisfied? 2. Compare your IR spectrum with that in the literature. Comment on the purity of your product. Reference: Merriam, J.S.; Niedenzu, K. Inorg. Synth. 1977, 17, 164.

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Part B. Synthesis of borane-t-butylamine complex Preamble: One of the most common reactions of boron to the reaction between the Lewis base BR3 and a Lewis acid such as NR’3 or PR’3. As many compounds BR3 are gaseous and poisonous (and therefore difficult to work with), this experiment will use a Brønsted-Lowry acid-base reaction between an ammonium acid and a borane base to form a R3B-N3 adduct. Synthesis of tert-butylammonium chloride, (CH3)3CNH3+Cl-: Dissolve 2.5 mL of tertbutylamine in 15 mL of anhydrous diethyl ether (hood). Add 2M HCl in diethyl ether gradually until precipitation is complete. Suction filter the product, wash with a little ether, and air dry on the frit. If storing for longer than a couple of hours, seal it in a bottle filled with N2 gas. Synthesis of the tert-butlyamine-boron adduct, (CH3)3CNH2-BH3: To a round-bottomed flask add 1.3 g of your tert-butylammonium chloride and 15 mL of dry tetrahydrofuran (THF). Stir the suspension with a magnetic stirrer, and add 0.20 mL of sodium borohydride, NaBH4 (hood). Place a drying tube over the neck of the flask. If the solution stops stirring, add a further 10-15 mL of THF. Note: H2 gas is released! Continue stirring for 2 hours. After the reaction has completed, suction filter the solution to remove NaCl and any unreacted (CH3)3CNH3+Cl-. Rotovap the THF solution to dryness to isolate your adduct product. Recrystallise the crude material by dissolving in a minimum of toluene (1-2 mL) and adding hexane until it precipitates. Determine the melting point. Questions: 1. Report your melting point. Comment on the purity of your product based on the melting point. 2. Using valence bond theory (Lewis structure), determine the direction of polarity of the N-B bond. Carry out the same analysis using molecular orbital theory. Do the two theories give you the same answer? Reference: Angelici, Robert J. Synthesis and Technique in Inorganic Chemistry. 2nd edition, p. 202. Philadelphia: Saunders. 1977.

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The Chemistry of Group 14 Carbon is well known for its ability to catenate; that is, to form long chains with many carbon-carbon bonds. The other non-metals in Group 14, also have this ability. Although the expense of germanium has limited its investigation, molecules containing catenated silicon are common. Even more common are the silicone materials, made up of polymers of chains of Si-O units. In Part 1 of this lab, you will synthesise and characterise two silicon polymers, one with a linear chain that is later converted into the second polymer, a cross-linked one. The metallic elements of Group 14, tin and lead, are now best known for their toxicity. The wealth of toxicity data arises from the fact that both metals have highly useful properties and are easy to isolate. They were readily available to even rudimentary civilisations. Tin compounds are often more dangerous, due to their higher volatility. Thus, in Part 2 of this experiment, you will investigate some lead compounds, on a small scale so as to limit waste. Part 1: Synthesis and Characterisation of Two Silicone Polymers Preamble: Dichlorodimethylsilane is toxic and volatile, so care must be taken when using this material. In addition, the compound readily hydrolyses in the air with the formation of (highly favourable) Si-O bonds, releasing HCl gas. In fact, we will use this reaction to form our silicon compounds, but we do not want to waste material in this way by leaving the cap off the bottle! The silicone oil is a linear polymer and is a liquid. The cross-linked polymer is much more viscous and has different properties than linear polymer Synthesis of silicone oil: Mix 20 mL of dichlorodimethylsilane with 40 mL of diethyl ether. Add 40 mL of water (dropwise) to the solution with stirring. Allow the layers to separate and wash the ether layer (containing your product) with dilute (10%) sodium bicarbonate solution until the washes have neutral pH. Then wash once with water and allow it to dry over magnesium sulfate. Decant and distill off the ether (rotovap) and record the yield and IR of the resultant oil. Synthesis of cross-linked silicone, “silly putty”: After performing all the necessary experiments above, place the oil in an evaporating dish (7 cm) with 1-5% by weight boric oxide. You may also add some celite (no more that 50% by weight) for filler. Heat this mixture, stirring occasionally with a glass rod, to 200°C for 20 minutes. Use a heating mantle, not a bunsen burner. Questions: 1. Report the spectrum of your oil and silly putty. Use a KBr disc for the silly putty, not nujol. Point out any differences between them. 2. Why can’t you use nujol when running the infrared spectrum of a silicone polymer?

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Part 2: Some Lead Chemistry Preamble: This experiment is cyclical, in that at the end, you will regenerate the starting material. Thus the expense (and environmental difficulties) of disposing of lead-contaminated waste is minimised. Both lead and formic acid are toxic substances, so this Part should be performed entirely in the fumehood. Be sure to dispose of all waste products (including decanted solutions, washings, etc.) in the lead waste container. Preparation and characterisation of lead(II) formate: In a medium-sized test tube, place 0.5 g of lead(II) acetate, Pb(CH3CO2)2.3H2O, and 3 mL of water. Immerse in a warm water bath (60-80°C) and stir with a glass rod until the solid dissolves. The clear solution is treated with 1 mL of 99% formic acid. A white precipitate should form immediately. Cool the solution in an ice bath for at least 3 minutes, to allow full crystallisation of the lead formate. Decant off the mother liquor (dispose in the lead waste) and wash the crystals twice with 3 mL of acetone, decanting off the wash each time. Be sure to stir the mixture with your stir rod while washing to ensure full removal of residual acid or water. Place in an oven (60-80°C) for 15 minutes to dry. Record your yield. Test the product using drop tests. Test for formate ion with permanganate solution. Place 2 drops of acetic acid and 1 drop of 0.1 M KMnO4 on a watch glass. Addition of a small amount of solid lead formate should decolourise the solution upon mixing. Try the test of lead(II) acetate as well. Test for the presence of lead using the lead iodide test. Dissolve 10 mg of lead formate in 1 mL of water and add a few drops of 1 M sodium iodide (make this solution yourself, but as little as possible - 1 mL is more than enough). A colour change and precipitate indicates the presence of lead. Repeat the test with 1 M H2SO4 to further confirm the presence of lead. Preparation of elemental lead from lead(II) formate: Take half of your remaining lead acetate (after doing the tests above), which should be at least 100 mg, and place in a test tube. The other half will be used below (these two parts, preparation of Pb and preparation of PbO, below, should be done simultaneously). Be sure to record the mass of the tube and solid together. Place a glass wool plug over the open end of the tube. Then, place the tube in the tube furnace for 5 minutes (no longer!) at 300°C. Remove from the furnace, allow to cool, remove the glass wool plug, and reweigh the tube. Be sure to note the colour and consistency of the solid product. Preparation of lead(II) oxide from lead(II) formate: Take the other half of your lead(II) formate (that not used above) and place in another test tube. Be sure to measure the mass of both the tube and the material together. Heat this tube for at least 60 minutes in the tube furnace at 300°C. Be sure to record the appearance of the product at the end of the heating time.

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Reconversion of lead to lead(II) acetate starting material: Return your test tube containing elemental lead to the furnace, leaving it in for at least 60 minutes. Combine this solid with the solid obtained from the lead(II) oxide formation. Dissolve completely in 4 M acetic acid (this will require heating). Allow the acetic acid to evaporate (by leaving on a watch glass over a week in the fumehood). Test that you have recovered lead(II) acetate by comparing the IR spectra of it with the commercial acetate starting material. Questions: 1. What are the substances created in the two tests for lead that are performed on the lead(II) formate you produced? Why do these materials precipitate? 2. Why do you need glass wool covering the tube mouth in the preparation of elemental lead? 3. Commonly, in the preparation of elemental Pb, the measured yield exceeds the calculated yield. Suggest a reason for this. 4. Report the IR of commercial Pb(CH3CO2)2 (recall it’s a trihydrate) and the Pb(CH3CO2)2 that you synthesised. Comment on any differences. Reference: Arnàiz, F.J.; Pedrosa, M.R. J. Chem. Educ. 1999, 76, 1687.

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The Chemistry of Group 15 The Group 15 elements can be known collectively as the pnicogens (from the Greek word meaning to choke or stifle, referring to the fact that nitrogen is an inert asphyxiant). This term is not IUPAC approved, but is sometimes used in the chemical literature. Because of the odd number of electrons in the neutral atom, the pnicogens often have odd numbered oxidation states (+3 and +5 being the most common for P and lower). Additionally, many compound ions exist, such as NH4+, PF6-, and SbF6-. In the neutral compounds, the most common valencies are coordination numbers 3 and 5. In the case of C.N. 3, there will also be a lone pair; thus, many of these compounds are Lewis bases. Part 1 of this experiment is the synthesis of a common ligand in transition metal chemistry. Because of the lone pairs on phosphorus in this compound, they can act in a Lewis base sense by binding to a positive metal to make a metal complex. In this course, we are interested in the ligand primarily. In Part 2, the syntheses of a number of salts containing ions of Group 15 are given. A complete experiment will consist of completion of Part 1 and one of Compounds A or B in Part 2. Part 1: Synthesis of Diphos and a Nickel Complex of Diphos Preamble: This synthesis involves the use of liquid ammonia as a solvent and also to solvate electrons. The intense blue colour is consistent with electrons in solution. Free electrons are required to cleave a phenyl group from PPh2 to create PPh2-, which then reacts with dichloroethane to create the desired product, diphos, as shown, 2 e- + PPh3 6 PPh2- + Ph2 PPh2 + ClCH2CH2Cl 6 Ph2PCH2CH2PPh2 + 2 Cl-

There are two sites of binding on diphos (i.e., it is dibasic, because of the lone pairs on the phosphorus atoms), and usually both these phosphorus centres would bind to the same atom, as in the case of the nickel complex you will synthesise Synthesis of 1,2-bis(diphenylphosphino)ethane, diphos, Ph 2P-CH2CH2-PPh2: Weigh out 11.5 g of sodium metal into a beaker containing 30 mL of hexane. The purpose of the hexane is to wash off the mineral oil from the sodium. Also weigh out 5.7 g of triphenylphosphine. Set up the ammonia condensor in the fumehood as directed by the lab demonstrator. Be sure you add a magnetic stirrer to the flask! Condense in 75 mL of ammonia. Cut up the sodium into 10-20 small chunks and add slowly to the ammonia while stirring the solution. Do not add it too fast or it will boil over. Once all the sodium is added, add the triphenylphosphine, again taking care not to boil over. Make a solution of 6 g of dichloroethane in 1 mL of ether. Add this dropwise to the stirred 15-1

solution. Once all the dichloroethane is added, remove the ammonia condensor and allow the ammonia to evaporate. This could take some time (say, half an hour). Once the flask reaches room temperature, add 25 mL of water and shake the flask. Filter the solid in a Büchner funnel and wash with a further 25 mL of water and 4 times with 2 mL of methanol. Recrystallise the crude product in 150 mL of 1-propanol. Filter and air-dry on a Büchner funnel. Synthesis of [1,2-bis(diphenylphosphino)ethane]nickel(II) chloride, [(Ph2P)2C2H4]NiCl2: In 10 mL of warm 1-propanol, dissolve 0.16 g NiCl2.6H2O, adding methanol until the solid goes into solution. Add 0.25 g of your recrystallised diphos. Filter the resultant crystals and air dry on a Büchner funnel. Questions: 1. Record the IR of both diphos and the nickel complex. Point out any differences to verify that the diphos has complexed with the nickel. 2. What is the fate of the Ph- produced in the liquid ammonia reduction? Part 2: Synthesis of Group 15 ions In this part of the experiment, there is one compound with an ion for each of phosphorus, arsenic, and antimony. Because Sb has more metallic character that As or P, it makes a cation instead of an anion. Compound A: Orthoarsenic Acid and Ammonium Orthoarsenate, (NH4)3AsO4.3H2O Synthesis of orthoarsenic acid. This experiment is carried out in a fume hood. Place 10 mL of concentrated nitric acid in a dropping funnel, and add (dropwise) to 10 g of solid arsenic(III) oxide. Evolution of nitrogen oxides will occur. Heat the solution (hotplate) with stirring until the evolution of gas ceases. Decant off the solution and evaporate to dryness. After evaporation, add a minimum of water (filtering if necessary, through a glass frit), and heat the solution until the temperature reaches 130°C. Allow the solution to cool - it should be supersaturated with a honeylike consistency. Store half in a desiccator in the fridge at least overnight. The product will crystallise out during that time. The other half will be used in the next step. Synthesis of ammonium orthoarsenate. Bubble ammonia gas through the half of the solution you saved from above. White crystals of the product should form immediately. Filter on a glass frit. Questions: 1. It is possible to isolate other products from the saturated arsenic acid solution. What are they and how are they isolated?

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Reference: Handbook of Preparative Inorganic Chemistry, Vol. 1, 2nd Edition, Georg Brauer, editor, p. 602. New York: Academic Press. 1963.

Compound B: Antimony(III) Sulphate, Sb 2(SO4)3 and Antimony Oxysulfate, (SbO)2SO4 Synthesis of antimony(III) sulphate. Dissolve 10 g of antimony(III) oxide in 50 mL of hot, concentrated sulfuric acid. When dissolved, allow to cool. Wash the crystals that precipitate with xylene followed by ether. Synthesis of antimony oxysulphate. Take a portion of the above product and add to cold water. Stir and filter the solid. Dry at 100°C. Take an IR of both products to show that conversion from the Sb3+ to SbO+ has occurred. Use a KBr pellet. Questions: 1. Would bismuth be more or less likely to form cationic salts than antimony? Why? Reference: Advanced Practical Inorganic Chemistry, D.M. Adams and J.B. Raynor, p. 42. London: Wiley. 1965. Note: This book is not owned by the Trent Library - I have photocopied the relevant pages and made them available on reserve.

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The Chemistry of Group 16 The elements of Group 16 are known as the chalcogens (from the Greek word for bronze, due to the affinity of sulfur for soft metals such as copper). The four non-radioactive chalcogens (O, S, Se, Te) are highly variable in their physical and chemical properties. In spite of this, consecutive members of the group. Both O and S are strictly non-metals, with several allotropic forms. The heavier Se and Te have considerable metallic character in certain situations, but will also form small ions and molecules much the same as normal non-metals. It is important to note that selenium and tellurium are highly toxic, both in the native form and in low oxidation states, and must be treated as heavy metals such as mercury or cadmium. Certain forms have the ability to penetrate the skin, and thus any spill on the body must be immediately washed with copious amounts of soap and water. Higher oxidation states (say, +4 or greater) are much less toxic, but still should be handled with care. The penalty for carelessness for a Te or Se chemist is a severely restricted social life for several months, as the metabolites used by the body to eliminate these metals (through the sweat glands and respiration) smell like rotting garlic. All members of the chalcogens exist in multiple oxidation states, the most common being even numbers (-2 to +6). All members except oxygen commonly exist with valencies up to 6. In this experiment, you will synthesise a sulfur compound in Part 1, using an electrolytic cell. In Part 2, you will synthesise a compound containing either tellurium or selenium depending on your choice. Part 1: Synthesis of Potassium Peroxydisulfate, K2S2O8 Preamble: This synthesis involves use of an electrolytic cell. This cell provides electrons and an appropriate voltage to effect a redox reaction that would otherwise be unfavourable. A common example of this type of synthesis is the isolation of NaOH, Cl2, and H2 by the application of current to sea water. The Electrolysis Cell: The cell has been prepared for you. It consists of an anode made by sealing a platinum wire into 6 mm glass tubing. The length of anode that is in contact with the solution is about 5 cm. The cathode is a Pt wire wound around the glass tubing. The electrode assembly is inserted into a cork or rubber stopper that either contains a hole or is loosely fitted into the approximately 2 x 20 cm test tube. These measures allow gaseous reaction products to escape from the system. An adjustable power supply conveniently provides the 1.0 amp/cm2 current density required for the K2S2O8 preparation. Note that this amperage level is dangerous, and all electrode connections should be made with care. Synthesis of the potassium peroxydisulfate: Prepare a saturated solution of KHSO4 by saturating a solution of 150 mL of water and 60 mL of concentrated H2SO4 with K2SO4. About 40 g of K2SO4 will be required to prepare the solution. Cool the solution to 0°C in 16-1

an ice bath to ensure that precipitation of excess K2SO4 is complete. Pour the supernatant solution into the electrolysis cell and immerse the cell in an ice bath. Turn on the power supply (record the time and amperage) and adjust the amperage until the anode current density is 1 amp/cm2. The amperage required will be determined by the area of the anode, as noted in the earlier discussion. Use the amperage that is required by the area of your anode to achieve a 1 amp/cm2 current density. Allow the current to flow for 30 to 45 minutes, during which time white crystals of K2S2O8 collect on the bottom of the tube. The reaction will slow considerably toward the end of this period owing to depletion of HSO4-. The resistance of the solution to the current will generate sufficient heat to require replenishing the ice in the bath during electrolysis. After the reaction period, turn off the power supply and record the time. Suction-filter the K2S2O8 crystals and wash them on the frit, first with 95 per cent ethanol and finally with diethyl ether. In each washing stage, stop the suction, fill the fritted funnel with solvent, stir the contents thoroughly, then suction filter. This will ensure that all H2O is removed from the product. Determine the yield. Questions: 1. Write a balanced chemical equation for this reaction and calculate the percent yield. 2. From the amperage and time, calculate the current efficiency. 3. Draw a Lewis diagram (dot formula) for the S2O82- ion. 4. What is overvoltage? Use this concept to explain why the oxidation of water does not occur in preference to oxidation of the hydrogensulfate anion at the anode. Reference: Angelici, Robert J. Synthesis and Technique in Inorganic Chemistry. 2nd edition, p. 162. Philadelphia: Saunders. 1977.

Part 2: Synthesis of a Selenium- or Tellurium-Based Anion Synthesise one of compounds A, B, or C. Compound A: Sodium Selenopentathionate, Na2SeS4O6.3H2O Prepare a salt-ice bath. Dissolve 1.7 g of SeO2 in 2 mL of water and 10 mL of glacial acetic acid. Cool in the salt-ice bath to a temperature below 0°C. Dissolve 13 g of Na2S2O3.5H2O in 4 mL of water (this will probably require heating the solution to dissolve all the thiosulphate; if so, cool to room temperature after dissolution before proceeding). Add this solution to a dropping funnel and add over the course of 20 minutes, with stirring, to the SeO2 solution. Do not allow the reaction mixture to exceed 0°C!!! Do not allow the addition to proceed any more quickly, as the product will 16-2

decompose in a local excess of thiosulfate anion. After the addition is complete, add 15 mL of ethanol. Once crystallisation starts, add 5 mL of ether and cool on an ice bath for 15 minutes. Suction filter the crude product. To recrystallise, dissolve in a minimum (~5 mL) of 0.2 M HCl, and gravity filter to remove any insoluble particulates (your product will go into solution). Then add 10 mL of methanol and cool on ice to crystallise. Questions: 1. Write a balanced chemical reaction and calculate the percent yeild. 2. How would you remove the water of crystalisation if you wanted anhydrous sodium selenopentathionate? Reference: Handbook of Preparative Inorganic Chemistry, Vol. 1, 2nd Edition, Georg Brauer, editor, p. 434. New York: Academic Press. 1963. Compound B: Sodium Telluropentathionate, Na2TeS4O6.2H2O Prepare a salt-ice bath. Dissolve 1.9 g of TeO2 in 7.5 mL of conc. HCl and 7.5 mL of glacial acetic acid. Cool in the salt-ice bath to a temperature below 0°C. Dissolve 11 g of Na2S2O3.5H2O in 6 mL of water (this will probably require heating the solution to dissolve all the thiosulphate; if so, cool to room temperature after dissolution before proceeding). Add this solution to a dropping funnel and add over the course of 15 minutes, with stirring, to the TeO2 solution. Do not allow the reaction mixture to exceed 0°C!!! Do not allow the addition to proceed any more quickly, as the product will decompose in a local excess of thiosulfate anion. After the addition is complete, add 15 mL of ethanol and cool on an ice bath for 15 minutes. Suction filter the crude product. To recrystallise, dissolve in a minimum (~6 mL) of 0.2 M HCl, and gravity filter to remove any insoluble particulates (your product will go into solution). Then add 10 mL of methanol and cool on ice to crystallise. Questions: 1. Write a balanced chemical reaction and calculate the percent yeild. 2. How would you remove the water of crystalisation if you wanted anhydrous sodium telluropentathionate? Reference: Handbook of Preparative Inorganic Chemistry, Vol. 1, 2nd Edition, Georg Brauer, editor, p. 454. New York: Academic Press. 1963.

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Compound C: Telluric Acid, H6TeO6 Dissolve 1.25 g of KMnO4 in 35 mL of water. To a 250 mL Erlenmeyer flask, add 25 mL of water and 10 mL of conc. nitric acid. Dissolve 2.5 g of TeO2 in this mixture (this will require boiling the solution in the fume hood). While maintaining a gentle boil, add the KMnO4 solution in several portions. Once the addition is complete you should have a cloudy solution (due to suspended MnO2). Remove from the heat and add 30% H2O2 dropwise (CAREFULLY!) until the solution is clear (the peroxide reacts with the MnO2). Evaporate the solution to 12 mL total volume, then add 2.5 mL of conc. nitric acid. Leave this solution to crystallise at least overnight. Suction filter the crystals. If you want to recrystallise them, dissolve in a minimum of hot water, add 3 drops of conc. nitric acid, and let stand uncovered until your next lab period. Questions: 1. Write a balanced chemical reaction and calculate the percent yield. 2. Draw a Lewis structure for telluric acid. Based on the structure, determine the number of acidic protons the compound contains. Reference: Handbook of Preparative Inorganic Chemistry, Vol. 1, 2nd Edition, Georg Brauer, editor, p. 451. New York: Academic Press. 1963.

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The Chemistry of Group 17 One normally thinks of the halogen elements in terms of either their coloured elemental forms or as simple anions X-. There is a much wider chemistry of these elements, especially for the brave chemist who is willing to work with fluorine. As the most electronegative element, fluorine can form compounds with elements that are normally unreactive, including the nobel gas xenon. In addition, positive oxidation states in normally electronegative metals can be accessed, such as O2+ in OF2, and Cl3+ in ClF3. Unfortunately, fluorine and binary fluorine compounds (like HF) are notoriously difficult to work with as F etches glass (thus stainless steel equipment is required) and is highly toxic. Chlorine can often serve the same purpose as fluorine with a sufficiently electropositive element, such as iodine. Thus, interhalogen ions such as the anionic ICl4-, with I in the +3 oxidation state, can be isolated. Iodine itself can for a number of different anions, as it has a limited catenating ability. Thus, the complex ions I3- and I5- are well established. In fact, there is considerable evidence for a large series of such anions, including I7-, I9-, I182-, etc. Structural analysis implies that these complex polyiodides are in fact sets of I2 and I- linked together by weak bonds. For example, I7- could be considered as 3 I2 + I-. This is also the way these polyiodides behave in solution (i.e., they dissociate). In this lab, you will synthesise a compound that contains a polyhalogen anion, either Ix- or ICl4-. You will then analyse the compound for iodine content using a redox titration. Part 1: Synthesis of a Polyhalogen Anion Synthesise one of compounds A, B, or C. Note that both compounds A and B contain the Ix- anion, but the preparative details are different, leading to different values of x. Compound A: Preparation of a polyiodide salt, NMe4Ix Dissolve 2.5 g of I2 in 30 mL of cold methanol. This will require stirring for some time and crushing the iodine crystals, but do not heat the solution. Once dissolved, add 1.0 g of finely powdered (mortar and pestle) tetramethylammonium iodide, Me4NI. As you stir in the ammonium salt, metallic green plates should start to appear in the solution. Once all the Me4NI has disappeared, allow the solution to stand for at least an hour (it will keep for a week if covered with parafilm and left in the dark). Filter the product and wash with 5 mL of cold methanol. Reference: Popov, Alexander I., Buckles, Robert E. Inorg. Synth. 1957, 5, 167. Compound B: Preparation of a polyiodide salt, NMe4Iy

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Dissolve 2.5 g of I2 in 30 mL of hot methanol (hood). Add 0.5 g of tetramethylammonium iodide, Me4NI. Stir the solution, maintain the heat, but do not allow the solution to boil, until all the Me4NI has disappeared. Allow the solution to stand and cool undisturbed for at least 90 minutes (it will keep for a week if covered with parafilm and left in the dark). Decant off any remaining solvent, wash with 5 mL of cold methanol, and decant off the wash. Allow the crystals to air dry (no suction). Reference: Popov, Alexander I., Buckles, Robert E. Inorg. Synth. 1957, 5, 167. Results for Part 1 Be sure to record the yield of your product, and to hand in a small sample of your crystals for grading.

Part 2: Analysis of Product Preamble: Iodine can be analysed by a process called iodometry. By this method, iodine atoms in any sort of iodine-based molecule or ion can by released by reaction with a suitable compound. This converts all the iodine to elemental iodine (I2) or to iodide (I-), which is then titrated by a standard method. You must standardise and run your samples all in the same lab period, as thiosulfate solutions only last a few hours. Preparation and Standardisation of Thiosulfate Solution: You must prepare and standardise a solution of sodium thiosulfate. Dissolve approximately 12.5 g of sodium thiosulfate hydrate, Na2S2O32-.nH2O (n . 5), in 500 mL of water. This will give an approximately 0.1 M solution. Standardise the solution using dry potassium iodate, KIO3. Weigh out three 0.05 g samples of iodate in each of 3 Erlenmeyer flasks. Just before titrating each flask, add 10 mL of distilled water, excess (1 g - need not be accurate) KI, and, once all the KI is dissolved, 10 mL of 0.5 M HCl. The resultant solution will be dark brown. Titrate immediately with the thiosulfate solution until it turns straw coloured, then add a few drops of starch to give the solution a blue colour. Continue titrating to the starch end point (colourless). Repeat for the other two flasks. The standardisation reaction is shown in Reactions 1 and 2. 1 2 Analysis of Compounds A and B: Weigh out accurately two 0.2 g samples into Erlenmeyer flasks. Add 0.25 g of KI, dissolve in 20 mL of methanol, then add 20 mL of distilled water. Titrate to a starch endpoint as with the standardisation run. 17-2

Questions: 1. 2. 3. 4. 5.

Balance Reactions 1 and 2. Report the average molarity of your thiosulfate solution. Report the value of x or y if you synthesised one of compounds A or B. If you synthesised compound C, determine how close you are to the theoretical value of 1. Draw the Lewis structure of S2O32-. Which resonance structure is most likely? Explain your reasoning. How does the addition of KI to a titration of Ix- improve the accuracy of your titration?

Reference: Vogel, Arthur I. A Textbook of Quantitative Inorganic Analysis. 3rd edition, p. 343. London: Longmans, Green, and Co. Ltd. 1961.

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