SamExamChem26Unit2v8 - Chemistry 26 Sample problems for...

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Chemistry 26 – Sample problems for Unit 2 (The actual exam will provide more space to show your work. Also, this practice exam is longer than the actual exam.) In addition to the following problems, Problems similar to those in the homework may also appear on the exam. Be aware that on the exam, some questions will only require an ICE table. Equations/Data: K w = 1.00 x 10 -14 a ac b b x 2 4 2 - ± - = - + = ] [ ] [ log HA A pKa pH Indicators and pH range of color change Methyl orange Methyl red Erichrome Black T Cresol red Alizarin yellow R 3.3 – 4.5 4.2 – 5.0 5.0 – 6.5 7.0 – 8.8 10.0 – 11.0 For the following multiple choice questions, CIRCLE the best answer. 1. For the equilibrium that exists in an aqueous solution of nitrous acid (HNO 2 , a weak acid), the  equilibrium constant expression is: a) K  =  b) K  =  c) K  = [H + ][NO 2 ] d) K  =  e) none of these 2. As water is heated, its pH decreases. This means that: a) the water is no longer neutral. b) the K w value is decreasing. c) the water has a lower [OH ] than cooler water. d) the dissociation of water is an endothermic process. e) none of these. 3. Which of the following is true for a buffered solution? a) The solution resists change in its [H + ]. b) The solution will not change its pH very much even if a concentrated acid is added. c) The solution will not change its pH very much even if a strong base is added. d) Any H + ions will react with a conjugate base of a weak acid already in solution. e) All of these 4. Which of the following will not produce buffered solutions? (There may be more than one answer!) a) 100 mL of 0.1 M Na 2 CO 3 and 50 mL of 0.1 M HCl b) 100 mL of 0.1 M Na 2 CO 3 and 75 mL of 0.2 M HCl c) 100 mL of 0.1 M NaHCO 3 and 25 mL of 0.2 M HCl
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d) 50 mL of 0.1 M NaHCO 3 and 30 mL of 0.4 M HCl e) 50 mL of 0.2 M Na 2 CO 3 and 5 mL of 1.0 M HCl f) 100 mL of 0.1 M Na 2 CO 3 and 50 mL of 0.1 M NaOH 5.   Using the following  K a  values, indicate the correct order of base strength (strongest base on the left,  weakest base on the right). HNO 2 K a  = 4.0  ×  10 –4 HF K a  = 7.2  ×  10 –4 HCN K a  = 6.2  ×  10 –10 a) CN  > NO 2  > F  > H 2 O > Cl b) Cl  > H 2 O > F –  > NO 2  > CN c) CN  > F  > NO 2  > Cl  > H 2 O d) H 2 O > CN  > NO 2  > F  > Cl e)
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This note was uploaded on 08/30/2010 for the course CHEMISTRY chem 26 taught by Professor Mitch during the Spring '10 term at Los Medanos College.

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SamExamChem26Unit2v8 - Chemistry 26 Sample problems for...

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