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Unformatted text preview: A. CLEARLY SHOW THE METHOD USED AND THE STEPS INVOLVED IN ARRIVING AT YOUR ANSWERS.
It is to your advantage to do this, since you may obtain partial credit if you do and you will receive little or no credit if
you do not. Attention should be paid to significant figures.
Be sure to write all your answers to the questions on the lined pages following each question in the booklet with the
pink cover. Do NOT write your answers on the green insert.
Answer Question 1 below. The Section II score weighting for this question is 20 percent.
1. Answer the following questions that relate to solubility of salts of lead and barium.
(a) A saturated solution is prepared by adding excess PbI2(s) to distilled water to form 1.0 L of solution at
25°C. The concentration of Pb2+ (aq) in the saturated solution is found to be 1.3 × 10 − 3 M . The chemical
equation for the dissolution of PbI2(s) in water is shown below. →
PbI2(s) ← Pb2+(aq) + 2 I −(aq)
(i) Write the equilibrium-constant expression for the equation.
(ii) Calculate the molar concentration of I −(aq) in the solution.
(iii) Calculate the value of the equilibrium constant, Ksp .
(b) A saturated solution is prepared by adding PbI2(s) to distilled water to form 2.0 L of solution at 25°C. What
are the molar concentrations of Pb2+ (aq) and I −(aq) in the solution? Justify your answer.
(c) Solid NaI is added to a saturated solution of PbI2 at 25°C. Assuming that the volume of the solution does
not change, does the molar concentration of Pb2+ (aq) in the solution increase, decrease, or remain the
same? Justify your answer.
(d) The value of Ksp for the salt BaCrO4 is 1.2 × 10−10. When a 500. mL sample of 8.2 × 10− 6 M Ba(NO3)2
is added to 500. mL of 8.2 × 10− 6 M Na2CrO4 , no precipitate is observed.
(i) Assuming that volumes are additive, calculate the molar concentrations of Ba2+ (aq) and CrO42−(aq)
in the 1.00 L of solution.
(ii) Use the molar concentrations of Ba2+ (aq) ions and CrO42−(aq) ions as determine...
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This note was uploaded on 10/01/2009 for the course OC 9876 taught by Professor Dq during the Spring '09 term at UC Merced.
- Spring '09