Montclair State University  CHEM 121 Laboratory Section

Experiment 5. Solubility Product of Copper Iodate

Moles of Cu(NH₃)₄²⁺ → Cu²⁺ + 4 NH₃

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Using 0.2 M (NH₄)₂S₂O_3, (standard ammonium thiosulfate solution), titrate the original 5 sample for concentration (m/L) of Iodate ion

Transfer 4.00 mL of original sample into a 250 or 125 mL flask and add the following in the order given:

1. 50 mL of water
2. 1 mL of 3M acetic acid
3. 1 g of potassium iodide (KI) crystals: swirl flask gently to dissolve the KI crystals
4.  add 5 mL of 1M sodium citrate solution.

Titrate with 0.2 M (NH₄)₂S₂O₃ solution until the iodine color fades to pale yellow. Add a small piece of starch flakes. Solution is now blue. Continue with titration until the first disappearance of the blue starch-iodine color. Record the volume used to reach the end point and calculate the moles of thiosulfate used to reach end point. Since you started with 4.00 mL of original sample, calculate the concentration of iodate in each sample.

Hint: Use the stoichiometric relationship of the following reactions involving the reaction of iodate ion from a saturated solution of copper iodate with potassium iodide:

Eqn 1:    IO₃^- + 5 I^- + 6 H⁺ → 3 I₂ + 3 H₂0

Eqn 2:    I₂  +  I^- → I₃^-

Eqn 3:   I₃^-  +  2 S₂O₃^2- → 3 I₃^- + S₄O₆^2-

Determine the ratio of the moles of thiosulfate reacted to the moles of iodate consumed to calculate the equilibrium concentration [IO₃^-] in m/L for the 5 samples.  NOTE: Put this ratio in your lab report:

Cu(IO₃)₂ → Cu⁺² + 2 IO₃^-

Ksp = [Cu⁺²] [IO₃^-]²

NOTE: If the solubility of Copper Iodate is 0.13 g/L, determine the Ksp from the solubility and compare to the value you determined experimentally. The molecular weight of Cu(IO₃)₂ is 413.3

Experiment 4. Potentiometric Titration and the Determination of Ka for a Weak Acid.

 Supplementary Review Docs and Tutorials on pH, Acids & Bases, Acid-Base Titrations.

1. Acids & Bases: Quick Review

2. Acid-Base Primer: A good basic primer on acids and bases

Read carefully the experiment for this week in the lab manual. Go over the introduction and the procedure very carefully so you are familiar with the experiment BEFORE you come to lab.  In your text book, read pages 623 thru 644 in Chapter 14 on Acids and Bases and pages 696 thru 709 in Chapter 15 on Titrations and pH curves.  Especially important are pages 705 thru 709 on the Titration of a Weak Acid and Calculating Ka value (Equilibrium Constant for the dissociation of the weak acid) for the acid in question. 

 In the lab, you will titrate an unknown weak acid with a strong base (NaHO),  determine the Ka, complete the titration curve and determine the unknown acid.  Make sure you write the unknown number for your sample on your lab report.

For more information on this subject, see my web site: http://www.techno-works.com/msu.htm

 Spend at least a few hours on all the above BEFORE lab period.  Come prepared!

 =Dr. Waldron

See Notes for Experiment 3 (Chemical Equilibrium)

Note on Experimental Report Writing:

Example of what is expected in a student lab report: For example - Experiment 3

There is a particular format for reporting experimental data and conclusions which was not followed by everyone in Experiment 1.

For example, many of you did NOT report in the Conclusion (or anywhere else in the report) just what the experiment was asking for (the experimental  heat of vaporization of water, ΔHvap, and the normal boiling point of water, Tb. Many left out all the sample calculations, and more importantly, the actual calculations needed to find the  ΔHvap from the slope of the linear equation as well as the calculation for Tb, from the intercept. In addition, many of you left out the published values of these physical constants and consequently could not report the % error for the two values. In other words, you didn't report what the experiment was asking!?

In addition, do NOT personalize any of the write-up in these reports. i.e  -. "My lab partner and I got good results" ......"we shot some water into the tube, etc etc" . "everything went as planned?!":.  "My lab buddy and I felt that the results were..."These are all no no's.....

Be totally objective, depersonalize all writing and just report the facts and what data you obtained. There is no mention of we, I, the two us us, etc.......

Carefully follow the outline below for Experiment 2:

Experiment 2: Kinetics 

Since part 2 of the lab was cancelled, you are only required to do part one of the lab. There is however many calculations you need to do and more importantly, know why you are doing them!

 Format of Report and what is expected for Experiment 2 

Please complete experimental reports using the exact format as below and in the same order. Also label your headings: INTRODUCTION & PURPOSE, PROCEDURE, etc, etc). Make sure you complete all the required parts below BEFORE you hand in Experiment 2.
 

Read and re-read very carefully  the entire experiment 2 (all pages)  before you begin analyzing the results.

 Cover Sheet with full name and date,  CHEM 121, Section number, experiment number and title of experiment

1.  INTRODUCTION & PURPOSE A paragraph or two summarizing the purpose of the experiment. In this case, explain the rate law for a generalized chemical reaction,  show the overall reaction (Eqn 11) and state the full rate law using general values of x and y as order of reactants and iodide ion and peroxydisulfate ion as reactants, show how you will determine the order of this reaction by the method of relative rates (or initial rate data), how each reactant is used to determine it's respective order in the rate equation by holding one reactant constant and changing the concentration of the other reactant. and and how the 'clock' reaction is used to determine the rate at which iodide ion (I^-) is oxidized by peroxydisulfate ion(S₂O₈^2-). Show all reactions and equations used.
    
2.  PROCEDURE Half page or one page summary of the procedure you used to measure the times observed in the clock reaction. What chemical were used in the 250 mL flask (solutions A, B and C) and what solutions were used in the 125 mL flask (D and E). What reations are involved here?
    
3.  DATA SECTION & EXPERIMENTAL RESULTS Put all  the raw data from the experiment  in tabular form or in spreadsheet (Excel) format. Put the data from PART I (Determination of the Rate Law) of the lab manual in tabular format (print out Excel data sheet using columns A through G in the lab manual under Data Analysis. You should have 2 experimental times for each run (1a,  1b, 2a, 2b, etc up to 4b). Fill in the concentrations (columns B and C) using dilution equation.  Find the average rate for each of the 4 runs (avg 1a and 1b, etc) from averaging the results from column E and putting the average results in column F for each of the 4 runs. You should now have one average rate of reaction listed for each reaction numbered 1 thru 4.
   
   Use your experimental results and the method of relative rates for experimental results (Equation 7 in the lab manual) to determine the values of x and y (order of reactants) in the rate law.  Finally, after determining the rate law, use the values of [I^-], [S₂O₈^2-] and the average reaction arte from each reaction to solve for the rate constant (k) for each run. Then average these results and report an average rate constant (k) for all your 4 runs and the average temperature of the experimental runs . In addition , show the units for the rate constant based on your experimental rate law that you just determined.
    
4. SAMPLE CALCULATIONS.  Apart from the tabulated data (Excel, etc) show  sample calculations for each 'type' of tabulated data. directly after the DATA & EXPERIMENTAL RESULTS SECTON)  For example, the thiosulfate ion, S₂O₃^2-, concentration  (which should be constant), an iodide concentration, a peroxydisulfate concentration, a reaction rate, an average reation rate and a rate constant calculation k, etc.
    
5. CONCLUSIONS. This is where you report your final results.  Show your experimental rate law here after showing the reaction that you investigated which is the iodide ion oxidized by peroxydisulfate:
   
   Show the reaction you studied, Then show your experimental results in the form of the order of reaction with respect to iodide (x) and the order of reaction with respect to peroxydisulfate and then the overall order of reaction., Finally show the entire rate equation, rate = k [I^-]^x [S₂O₈^2-]^y  where k, x and y are numerical values. Don't forget the proper units for the rate constant, k (it depends on the overall reaction order).
    
6. SUPPLEMENTARY QUESTIONS.  Answer all the supplementary questions after  each experiment. Show all work, proper units and label all answers properly. If they involve equation(s) for the solution(s), show all equations used.
    
   
   Make sure your repots are stapled and handed in on time. These reports are due next lab period

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                        HAc + PrOH ↔ PrAc + H₂O

Supplementary Questions: Hints:

Running the reaction is aqueous solutions of acetic acid and n-propyl alcohol would case a dilution in the reactants. In your text on pp 604-610 , there are several ways a reaction can be controlled using the principles of Le Chatelier. Reviewing these pages will help you get the answers to the 2 supplementary questions.

                                     HAc          +         PrOH        ↔    PrAc             +        H₂O

K_eq = [3.75][3.75] /3.75][4.05] = 0.93 reaction goes to approx 50% completion (hypothetical)

Remember to use your won experimental values and not the hypothetical ones I used above. The only value that I used that should be same as your values is the initial concentration of PrOH.

 =Dr. Waldron, Chemistry Professor

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                                                                        Page last updated on 10/17/2007