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Exam 2 Solutions

# Exam 2 Solutions - Version 370 Exam 2 owers(53885 This...

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Version 370 – Exam 2 – flowers – (53885) 2 Using Henderson-Hasselbalch equation, pH = p K a + log parenleftBigg [HPO 2 - 4 ] [H 2 PO - 4 ] parenrightBigg 7 . 4 = 7 . 21 + log parenleftBigg [HPO 2 - 4 ] [H 2 PO - 4 ] parenrightBigg log parenleftBigg [HPO 2 - 4 ] [H 2 PO - 4 ] parenrightBigg = 0 . 19 [HPO 2 - 4 ] [H 2 PO - 4 ] = 10 0 . 19 = 1 . 54882 [Na 2 HPO 4 ] = (1 . 54882)(0 . 19 mol / L) = 0 . 294275 mol / L m Na 2 HPO 4 = 0 . 294275 mol(0 . 25 L) = 0 . 0735688 mol Na 2 HPO 4 Na 2 HPO 4 = 141 . 959 g/mol mass = (0 . 0735688)(141 . 959) = 10 . 4437 g Na 2 HPO 4 005 10.0 points What is the approximate pH of a solution in which the concentration of formic acid is 0.80 M and the concentration of sodium formate is 0.20 M? 1. 4.2 2. 4.8 3. 3.1 correct 4. 3.7 5. 1.6 Explanation: [F - ] = 0.20 M [HF] = 0.80 M K a = 1 . 8 × 10 - 4 pH = p K a + log parenleftBigg bracketleftbig F - bracketrightbig [HF] parenrightBigg = log(1 . 8 × 10 - 4 ) + log parenleftbigg 0 . 2 0 . 8 parenrightbigg = 3 . 14267 006 10.0 points An acidic fog in Pasadena was found to have a pH of 2.5. Which expression represents this pH measurement? 1. M H + = 2 . 5 M 2. M H + = 9 . 7 × 10 - 3 M 3. M OH - = 3 . 16 × 10 - 9 M 4. M OH - = 3 . 16 × 10 - 12 M correct Explanation: pH= 2 . 5, so M H + = 10 - 2 . 5 = 0 . 00316228M and M OH - = 1 × 10 - 14 M H + = 1 × 10 - 14 0 . 00316228 = 3 . 16228 × 10 - 12 M 007 10.0 points What is K sp for Ag 3 PO 4 , if its molar solubility is 2 . 7 × 10 - 6 mol / L?
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