CH 302 - [McCord] [Spring 2010] - Test 2

CH 302 - [McCord] [Spring 2010] - Test 2 - Version 088 –...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Version 088 – Exam 2 – Mccord – (52450) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. McCord CH302 1pm This exam is only for McCord’s MWF 1pm CH302 class. 001 10.0 points The equilibrium constant for the reaction 2 SO 2 (g) + O 2 (g) ⇀ ↽ 2 SO 3 (g) has the value K = 4 × 10 24 at 298 K. Find the value of K for the reaction SO 3 (g) ⇀ ↽ SO 2 (g) + 1 2 O 2 (g) at the same temperature. 1. 5 × 10 − 13 correct 2. 5 . 77 × 10 − 3 3. 3 . 95 × 10 − 10 4. 2 . 64 × 10 − 7 5. 6 . 32 × 10 − 6 6. 8 . 23 × 10 − 8 Explanation: For the first equation 2 SO 2 (g) + O 2 (g) ⇀ ↽ 2 SO 3 (g) K 1 = P 2 SO 3 P 2 SO 2 · P O 2 = 4 × 10 24 . For the second reaction SO 3 (g) ⇀ ↽ SO 2 (g) + 1 2 O 2 K = P SO 2 · P 1 / 2 O 2 P SO 3 = 1 √ K 1 = 1 √ 4 × 10 24 = 5 × 10 − 13 002 10.0 points A solution of HClO is mixed and found to have a pH of 4 . 74. Find what the initial concentration of HClO was for this solution. K a = 3 . 00 × 10 − 8 for HClO. 1. 0.10072 2. 0.191889 3. 0.0110559 4. 0.210399 5. 0.0553603 6. 0.0290616 7. 0.481933 8. 0.139021 9. 0.021057 10. 0.0220488 Correct answer: 0 . 0110559 mol / L. Explanation: pH = 4 . 74 K a = 3 × 10 − 8 At equilibrium, [H 3 O + ] = 10 − pH = 10 − 4 . 74 = 1 . 8197 × 10 − 5 mol / L . Analizing the reaction using concentra- tions, HClO + H 2 O ⇀ ↽ H 3 O + + ClO − C − − x − x x C − x − x x x = [H 3 O + ], so K a = x 2 C − x C − x = x 2 K a Version 088 – Exam 2 – Mccord – (52450) 2 C = x 2 K a + x = (1 . 8197 × 10 − 5 ) 2 3 × 10 − 8 + 1 . 8197 × 10 − 5 = 0 . 0110559 mol / L . 003 10.0 points Auto-protolysis of water is the same as the autoionization of water. Consider a glass of water at 80 ◦ C, which of the following statements is true? 1. The water is acidic because its pH is slightly lower than 7 2. The water is neutral because its pH is 7 3. The concentrations of H + and OH − are equal correct 4. The auto-protolysis of water is an exothermic process Explanation: The auto-protolysis of water is an endother- mic process since energy is needed to break the bonds. At a higher temperature, more H + ions exist due to higher energy, thus the pH of water decreases. The water is not acidic be- cause pH = pOH, although the K w is not 14 in this case. 004 10.0 points Rank following acids from most to least acidic: hydrocyanic acid (HCN) K a = 6 . 2 × 10 − 10 hypoiodous acid (HOI) K a = 2 × 10 − 11 chlorous acid (HClO 2 ) K a = 1 . 2 × 10 − 2 acetic acid (CH 3 COOH) K a = 1 . 8 × 10 − 5 1. HOI > HClO 2 > CH 3 COOH > HCN 2. CH 3 COOH > HCN > HOI > HClO 2 3. HCN > HOI > HClO 2 > CH 3 COOH 4. HClO 2 > CH 3 COOH > HCN > HOI correct Explanation: Explanation: The value of K a is directly proportional to the acidity (strength) of the acid. By ranking from the largest (1 . 2 × 10 − 2 ) to the smallest (2 × 10 − 11 ) Ka, one is ranking from the most to least acidic.from the most to least acidic....
View Full Document

This note was uploaded on 11/18/2010 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas at Austin.

Page1 / 10

CH 302 - [McCord] [Spring 2010] - Test 2 - Version 088 –...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online