Chemistry 2604 Name: ______L. S. Curtin Soc. Sec. #. ______March 7, 2007

EXAM I

INSTRUCTIONS:

Follow the instructions given to you below. Failure to follow these instructions will result in a significant deduction of points from your exam score.

1) This exam consists of nine pages, the last being a table of equilibrium constants and a periodic table. If any of the pages are missing bring your exam to me immediately .

2) Make sure to print your name and social security number in the top, right hand corner of the exam.

3) Answer five and only five of the six questions on the exam. Clearly indicate which of the questions you do not want to be graded by putting an X through the entire page the question is on.

4) You must show ALL of your work in order to receive credit for an answer, no matter how trivial it may seem. Work must be presented in an orderly and easily followed way . Show all of your units in your calculations and pay attention to the number of significant figures in your responses.

5) You will receive 50 minutes to take the exam . Budget your time for each question and answer questions which you know how to work first. After you have finished the entire exam, it is a good practice to review and check your work.

6) Good luck!

1) Fully explain why the solubility of chloride in 0.10 M aqueous ammonia is higher than it is in pure water. Note that I am not interested in calculating the increased solubility, I am interested in an explanation . 2) 10.00 mL of an aqueous solution which is 0.1000 M in NaClO 3 is mixed with 25.00 mL of an aqueous solution which is 0.02500 M in HBr. Calculate the pH of the resulting solution.

3) Consider Experiment 3: Volumetric Chloride:

a) Suppose that a student accurately weighed out the appropriate amount of dried sodium chloride, covered the sample with parafilm and waited until the next lab period to dissolve the sample before proceeding with the titration. Assuming that the student correctly performed the rest of the titration as outlined in the lab, would the calculated molarity of the silver nitrate solution be accurate, too high or too low? Fully explain your response.

b) b) Suppose that a student did a similar thing in Experiment 4: Percentage of Copper in an Oxide. The student accurately weighed out the appropriate amount of copper wire which had been cleaned as indicated in the lab, covered the sample with parafilm and waited until the next lab period to dissolve the sample before proceeding with the laboratory procedure. Assuming that the student correctly performed the rest of the titration as outlined in the lab, would the calculated molarity of the thiosulfate solution be accurate, too high or too low? Fully explain your response.

4) The solubility of nickel sulfide in 0.50 M aqueous sodium cyanide solution is 1.37 x 10 -3 M. Calculate the solubility of nickel sulfide in pure water.

5) Consider Experiment 3: Volumetric Chloride in which sodium chloride was titrated via the Mohr method using potassium chromate as the indicator. Given that the initial concentration of potassium chromate was 2 x 10 -3 M, calculate the percent error in the titration when 50.00 mL of an aqueous solution which was 0.100 M in sodium chloride was titrated with 0.100 M silver nitrate solution. (Note: the potassium chromate solution was added prior to dilution of the sodium chloride)

6) Give the correct name or for the following compounds: a) H3PO 3(aq)

b) Ca(IO) 2

c) Permanganic acid

d) Stannous bicarbonate

Some Potentially Useful Equilibrium Constants

Acid Ka Base Kb Acetic 1.75 x 10 -5 Ammonia 1.75 x 10 -5 Chlorous 1.12 x 10 -2 Aniline 3.94 x 10 -10 Hypochlorous 3.0 x 10 -3 Dimethylamine 5.9 x 10 -4 Hydrocyanic 4.9 x 10 -10 Ethylamine 4.28 x 10 -4 Hydrofluoric 6.8 x 10 -4 Hydroxylamine 1.07 x 10 -8 Nitrous 5.1 x 10 -4 Methylamine 4.8 x 10 -4 Phthalic acid 1.2 x 10 -3 Hydrogen phthalate 3.9 x 10 -6 Pyridine 1.7 x 10 -9 Methyl red 1.25 x 10 -5 THAM 1.19 x 10 -6

Salt Ksp Aluminum hydroxide 2 x 10 -32 Barium chromate 1.2 x 10 –10 Calcium carbonate 4.5 x 10 -9 Calcium sulfate 2.6 x 10 –5 Copper(I) sulfide 2.0 x 10 –47 Copper(II)sulfide 8.5 x 10 -45 Iron(III) hydroxide 4.0 x 10 -38 Lead(II) chromate 1.77 x 10 -14 Lead(II) iodide 7.47 x 10 -9 Lead oxalate 4.8 x 10 -10 Lead sulfate 1.6 x 10 -8 Mercury(I) bromide 6.4 x 10 -23 Mercury(II) bromide 1.56 X 10 -12 5.2 x 10 -13 Silver carbonate 1.8 x 10 -10 Silver chromate 1.1 x 10 -12 Silver dichromate 2.0 x 10 -7 8.3 x 10 -17 Zinc sulfide 4.5 x 10 -24

Complex ion Kf + 6 Ag(NH 3)2 1.3 x 10 2- AgBr 3 5.0 - 21 Ag(CN) 2 1.26 x 10 2- 22 Ni(CN) 4 1.0 x 10