Industrial Chemistry Quiz 4 With Answers

UPH Industrial Chemistry

2009

Name: __________________ Date: __________________

Student ID: _____________ Marks: ____/100

Quiz 4 Instruction: Please write your answers legibly. 1. Oxoanions of phosphorous are buffer components in blood. For a KH2PO4/Na2HPO4 solution with pH = 7.40 (pH of normal arterial blood), what is the buffer-component concentration ratio? Answer: 1.6 2. A 50.0-ml volume of 0.50 M Fe(NO3)3 is mixed with 125 ml of 0.25 M Cd(NO3)2. (a) If aqueous NaOH is added, which ion precipitates first? (see Appendix C) (b) Describe how the metal ions can be separated using NaOH. (c) Calculate the [OH-] what will accomplish the separation. Answer: (a) Fe(OH)3 (b) The two metal ions are separated by adding just enough NaOH to precipitate iron(III) hydroxide. (c) 2.0 × 10-7 M 3. Find the solubility of Cr(OH)3 in a buffer of pH 13.0. Given that Ksp of Cr(OH)3 = 6.3 × 10-31; Kf of Cr(OH)4- = 8.0 × 1029. pOH =1, so [OH-] = 0.1 Cr(OH)3 +

OH-  0.1 -S 0.1 - S

Cr(OH)4+S S

Koverall = Ksp × Kf = [Cr(OH)4-]/[ OH-] Answer: 0.034 M

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UPH Industrial Chemistry

2009

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