Exam I master Page 1 Chemistry 103B Exam 2 Answer Key Form B 1. (2) Which acid/<a href="/keyword/conjugate-base/" >conjugate base</a> pair would be best for making a buffer solution with pH = 3.00? (a) H3 PO4 / H2 PO4 - (b) HCO3 /CO3 2- (c) H2 CO3 /HCO3 - (d) HCN/CN - (e) CH3 OH/CH3 O - Essentially from the d2l practice test. Definition of pH 2. (2) Lead(II) iodide, PbI2 (s), has Ksp = 7.9e-9. What is the concentration of iodide ion, I (aq), in a saturated solution of PbI2 ? (a) 1.3e-3 M (b) 2.5e-3 M (c) 2.0e-3 M (d) 6.3e-5 M (e) 1.3e-4 M - From the study outline : &quot;Be able to calculate the pH or hydrogen ion concentration of a buffer solution given the equilibrium concentrations of the weak acid , its <a href="/keyword/conjugate-base/" >conjugate base</a> and the appropriate Ka .&quot; 3. (2) A water solution has a pH of 0.00. This means: (a) The solution is neutral. (b) the hydrogen ion concentration is 1.00 mol/L (c) There is no hydronium ion present . (d) There is no hydroxide ion present . (e) The hydrogen ion concentration is 0.00 mol/L. 4. (2) What is pH of a buffer solution that consists of 0.10 M HCO3 (aq) and 0.95 M CO3 (aq)? (a) 8.80 (b) 11.29 (c) 7.27 (d) 4.66 (e) 9.33 - - From the study outline : &quot;Understand how the strength of an oxyacid depends upon molecular structure .&quot; 5. (2) A pH value greater than 13.00 means (a) [OH ] &gt; 0.10 M - (b) [H ] &gt; 0.10 M + (c) [OH ] &lt; 0.10 M - (d) [H ] &lt; 0.10 M + (e) none of these http://www.chem.arizona.edu/~kellerp/exams/Exam2/exam2Ban/Exam2Ban.htm 4/10/2008 12:20:38 AM Exam I master Page 2 (a) [OH ] &gt; 0.10 M - (b) [H ] &gt; 0.10 M + (c) [OH ] &lt; 0.10 M - (d) [H ] &lt; 0.10 M + (e) none of these 6. (2) Choose the strongest acid. (a) (b) (c) (d) (e) Be able to find the equilibrium concentrations of all species in a solution of a diprotic acid . 7. (2) A diprotic acid H2 A has Ka1 = 4.0 x 10 and Ka2 = 6.0 x 10 what is [A ]? (a) 6.0 x 10 -12 2-7 -12 . In a 0.10 mol/L solution of this acid, M (b) 4.0 x 10 M -6 (c) 6.3 x 10 M -4 (d) 4.5 x 10 M -3 (e) 1.4 x 10 M -3 From the d2l practice test. 8. (2) A diprotic acid H2 A has Ka1 = 4.0 x 10 and Ka2 = 6.0 x 10 what is [H3 O ]? (a) 4.5 x 10 M -3 + -7 -12 . In a 0.10 mol/L solution of this acid, (b) 2.5 x 10 M -6 (c) 0.10 M (d) 1.4 x 10 M -4 (e) 2.0 x 10 M -4 From the study outline : Be able to explain why a 0.10 mol/L solution of sulfuric acid has a lower pH than a 0.10 mol/L solution of hydrochloric acid . 9. (2) A phosphate buffer (H2 PO4 /HPO4 ) has a pH of 8.3. Which of the following willcause the pH to increase ? (a) Adding a small amount of phosphoric acid (H3 PO4 ) (b) Dissolving a small amount of NaH2 PO4 . (c) Adding a small amount of hydrochloric acid. (d) Making the buffer more concentrated by removing some water by evaporation . (e) Adding a small amount of Na2 HPO4 . 2- 10. (2) Which of the 0.10 mol/L solutions willhave a pH less than 1.00? (a) H2 SO4 (aq) (b) HClO4 (aq) (c) HF(aq) (d) HNO3 (aq) (e) CH3 OH(aq) http://www.chem.arizona.edu/~kellerp/exams/Exam2/exam2Ban/Exam2Ban.htm 4/10/2008 12:20:38 AM Exam I master Page 3 (a) H2 SO4 (aq) (b) HClO4 (aq) (c) HF(aq) (d) HNO3 (aq) (e) CH3 OH(aq) 11. (2) Potassium hydroxide (KOH) is an ionic compound and a strong base. A water solution of KOH has a pH of 12.83. Find the mol/L concentration of potassium ion in this solution (a) 1.0e-7 M (b) 1.17 M (c) 0.068 M (d) 1.5e-13 M (e) 12.83 M 12. (2) Which acid/<a href="/keyword/conjugate-base/" >conjugate base</a> pair would not make a buffer solution ? (a) NH4 /NH3 + (b) HF/F - (c) H2 S/HS - (d) H2 SO3 /HSO3 - (e) HNO3 /NO3 - 13. (2) Calciumcarbonate , CaCO3 , is only slightly soluble in water. Ksp = 4.0 x 10 . If more Ca (aq) is added to a saturated water solution of calcium carbonate (a) some solid CaCO3 willform (b) some solid CaCO3 will dissolve (c) the concentration of carbonate ion will increase (d) the concentration of calcium ion will drop below 2.0 x 10 M -4 -8 2+ (e) none of these The weakest base will be the conjugate of the strongest acid . From the study outline : &quot;Understand and be able to explain the meaning of all regions of the acid <a href="/keyword/conjugate-base/" >conjugate base</a> table shown in lecture and on problem set 4 and 5.&quot; 14. (2) Acetate ion is the <a href="/keyword/conjugate-base/" >conjugate base</a> of acetic acid, HCH3 CO2 . A solution is prepared by dissolving 0.10 mol of potassium acetate (KCH3 CO2 ) in 1.0 L of pure water. Which statement about the solution is correct? (a) [OH ] &gt; [H3 O + - (b) The pH is less than 7.0 (c) The solution is neutral. ] (d) The concentration of potassium ion is less than 0.10 M. (e) The concentration of acetate ion willbe 10 M. -7 From the study outline : &quot;Understand and be able to explain the meaning of all regions of the acid <a href="/keyword/conjugate-base/" >conjugate base</a> table shown in lecture and on problem set 4 and 5.&quot; 15. (2) Which acid has the weakest <a href="/keyword/conjugate-base/" >conjugate base</a> ? http://www.chem.arizona.edu/~kellerp/exams/Exam2/exam2Ban/Exam2Ban.htm 4/10/2008 12:20:38 AM Exam I master Page 4 15. (2) Which acid has the weakest <a href="/keyword/conjugate-base/" >conjugate base</a> ? (a) HCl (b) HF (c) HCN (d) HCH3 CO2 (e) HOCl From the study outline : &quot;Predicting the qualitative strength of an acid by examination of its structural formula.&quot; 16. (2) This question involves interpretation of the acid-base table attached to this exam. Which substance is a stronger proton donor than water? (a) ClO4 - (b) F - (c) CH3 - (d) HCN (e) CH3 OH From the study outline : &quot;Understand and be able to explain the meaning of all regions of the acid <a href="/keyword/conjugate-base/" >conjugate base</a> table shown in lecture and on problem set 4 and 5.&quot; 17. (2) Choose the weakest proton donor . (a) (b) (c) (d) (e) From the study outline : &quot;Be able to calculate Kb for the <a href="/keyword/conjugate-base/" >conjugate base</a> of a weak acid given the Ka value of the acid .&quot; 18. (2) This question involves interpretation of the acid-base table attached to this exam. Which substance is a weaker proton acceptor than water? (a) HCN (b) HCl (c) ClO4 - (d) HClO4 (e) NH4 + 19. (2) What is the value of Kb for the <a href="/keyword/conjugate-base/" >conjugate base</a> of formic acid (HCO2 H). Ka = 2.1 x 10 (a) 4.8 x 10 -11 -4 (b) 4.4 x 10 -8 (c) 4.8 x 10 3 (d) 2.1 x 10 -18 (e) -2.1 x 10 -4 Definitions of pOH and pH. pOH = 14.00 14.85 = -0.85 [OH ] = 10 -pOH = 10 0.85 = 7.1 mol/L http://www.chem.arizona.edu/~kellerp/exams/Exam2/exam2Ban/Exam2Ban.htm 4/10/2008 12:20:38 AM Exam I master Page 5 http://www.chem.arizona.edu/~kellerp/exams/Exam2/exam2Ban/Exam2Ban.htm 4/10/2008 12:20:38 AM