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Unformatted text preview: Chem 126 Common 2 Spring March 11, 2011 NONE OF THE MULTIPLE CHOICE PROBLEMS REQUIRES EXTENSIVE OR TIME COMSUMING CALCULATIONS. IF YOUR METHOD REQUIRES EXTENSTIVE CALCULATIONS IT IS EITHER WRONG OR HARDER THAN WHAT IS REQUIRED. 1. The pH of a nitric acid, HNO 3 , solution is 1.43. What is the concentration of the nitrate ion? (a) 7.24 x 10-12 M (b) 1.38 x 10-3 M (c) 2.69 x 10-13 M (d) 3.72 x 10-2 M (e) none of the above 2. Calculate the pH of a 0.005 M aqueous barium hydroxide solution, ( 29 2 . Ba OH Careful. (a) 2.30 (b) 11.70 (c) 2.00 (d) 12.00 (e) 8.70 3. A solution consists of 0.080 M HCl, 0.055 M HBr, and 0.045 M HCN. What is the pH? (a) 0.23 (b) 0.87 (c) 1.10 (d) 1.26 (e) Insufficient information 4. What is the pH of a solution formed by mixing 70. mL of 0.25 M 4 HClO (perchloric acid) and 140 mL of 0.15 M NaOH? (a) 2.46 (b) 11.54 (c) 12.22 (d) 12.40 (e) 1.78 5. A 0.142 M aqueous solution of a weak acid, HB, has a pH of 1.50. Calculate K a , the acid-dissociation constant. (a) 7.2x10-3 M (b) 7.0x10-3 M (c) 0.22 M (d) 1.0x10-3 M (e) none of the above 1.43 log . So, 10 10 0.0372 pH pH H H M + +-- = - = = = ( 29 2 0.005 0.01 ; log 0.01 2.00; 14 12.00 OH x M pOH pH pOH- = = = - = =- = is a weak acid. So, its concentration can be ignored compared to a strong acid. Both HCl and HBr are strong acids. 0.08 0.055 0.135 ; log 0.87 HCN H M pH H + + = + = = - = 0.25 70 17.5 1 0.15 140 21 1 mol mL mmol H x mmol L mol mL mmol OH x mmol L +- = = = = ( 29 ( 29 ( 29 ( 29 2 17.5 21 - C -17.5 -17.5 - 3.5 E 0 3.5mmol 0.0167 210 log 0.0167 1.78; 14 H aq OH aq H O l I mmol OH M mL pOH pH +-- + → = = = - = = 12.22 pOH- = [ ] 1.50 10 10 0.0316 0.142 0.316 0.139 pH x H M HB M +-- = = = = =- = ( 29 ( 29 ( 29 ( 29 2 0.142M - 0 C -x +x +x E 0.142-x x x HB aq H O l H aq B aq I +- + → + [ ] ( 29 2 3 0.0316 = = 9.0 10 0.139 a H B M K x M HB M +-- = Chem 126 Common 2 Spring March 11, 2011 6. A carbonated drink is bottled under a fixed pressure of carbon dioxide. Which of the following stresses increases the concentration of the carbonate ion, CO 3 2- ? (Use Le Chatelier’s principle) P CO2 + H 2 O (l) ↔ CO 2 (aq) CO 2 (aq) + 2H 2 O (l) ↔ H 3 O + (aq) + HCO 3- (aq) HCO 3- (aq) + H 2 O (l) ↔ H 3 O + (aq) + CO 3 2- (aq) (a) The carbon dioxide pressure is decreased. 2 Stress: too little . So, each reaction goes to left. CO P (b) Phosphoric acid is added to the water before the carbonation step (above reactions). (c) Sodium Iodide is added to the water before the carbonation step. No effect. (d) Sodium hydroxide is added to the water before the carbonation step....
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