Honors General Chemistry Test 3 Prof. Shattuck, practice

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1 Honors General Chemistry Test 3 Prof. Shattuck, practice Name R = J mol -1 K -1 1 L atm = J T(0 C) = K Answer 8 of the following 10 questions. If you answer more than 8 cross out the ones you wish not to be graded, otherwise only the first 8 will be graded. (6 points each) 1. Is PbBr2 more soluble in : (a) pure water, (b) 0.10 M NaBr, or (c) 0.10 M Pb(NO3)2? 2. Circle the stronger acid in each pair: (a) HF, HBr (b) H3PO4, H3PO3 (c) HClO3, HBrO3 3. Write the reactions that show why CaCO3(s) has increasing solubility with decreasing ph. CaCO3 (s) Ca 2+ (aq) + CO3 2- (aq) with CO3 2- (aq) + H + (aq) HCO3 or CaCO3 (s) H + Ca 2+ (aq) + HCO3 (aq) or CaCO3 (s) + H2O (l) Ca 2+ (aq) + HCO3 (aq) + OH with H + + OH H2O (l) 4. Are aqueous solutions of the following acidic, basic, or neutral? (a) NH4Cl _acidic (b) KNO3 neutral (c) Na2SO4 basic 5. Consider the general reagents at 0.1 M concentration: HCl, H2SO4, NH3, NaOH. Which of these four reagents do you add to get the following precipitates to dissolve? You can use each reagent only once (in other words you will use all four choices). (a). To dissolve Cu(OH)2 (s) add HCl _or H2SO4 (b). To dissolve Zn(OH)2 (s) add NaOH (c). To dissolve AgCl (s) add NH3 (d). To dissolve CaF2 (s) add HCl _or H2SO4 6. In the titration of ammonia with strong acid, is the equivalence point acidic, basic, or neutral? Show the reaction that determines the ph. 7. What are the two conjugate acid base pairs in the reaction: H2PO4 - + H2O H3PO4 + OH base acid acid base Make sure to indicate which in each pair is the acid and which the base. 8. For the following reactions, does the equilibrium position lie to the or right? (a) F + H2O HF + OH (b) HF + H2O F + H3O +

2 9. The volume of an ideal gas is increased from 1.00 L to 5.00 L at a constant pressure of 2.00 atm. Assume q = 0 and calculate the change in internal energy for this process. Remember to convert to J: (not this year) 10. Name the following compounds: Part II. (a) HIO hypoiodous acid (b) H3PO4 phosphoric acid (c) Na2SO3 sodium sulfite 11. Calculate the concentration of Cu 2+ in a solution of M Cu(NH3)4 2+, with an ammonia concentration of 0.20 M. The formation constant is: Cu 2+ (aq) + 4 NH3 (aq) Cu(NH3)4 2+ (aq) Kf = 5.0x Cu(NH3)4 2+ Cu NH3 Kd = 1/Kf = 2.0x10-13 initial change x +x +4x equil x x x Kd = 1/Kf = 2.0x10-13 = [Cu2+ ][NH3] 4 [ Cu(NH3)4 2+ ] = x(0.20+4x) x x(0.20) x = 1.25 x10-13 M 12. Calculate the ph at the equivalence point of a titration of 30.0 ml of M HClO with M NaOH. For HClO, Ka = 1.1x10-8 M. Show the reaction that determines the ph. reaction that determines the ph: ClO HClO + OH equil: x x x Kb = 1x10-14 /1.1x10-8 = 9.09x10-7 = [HClO][OH ] [ClO ] = x x x [OH ] = x = cbkb = (9.09x10-7 ) = 2.13x10-4 and poh = ph = What is the ph of a solution prepared by adding 1.00 L of 0.25 M HCl to 1.00 L of 0.40 M ammonia. For ammonium ion Ka = 5.5x10-10 M. The reaction with strong acid gives: NH3 + H + NH4 + (assume goes to completion) initial 0.40 mol 0.25 mol 0 completion 0.15 mol mol [H + ] Ka ca cb = Ka na nb [H + ] 5.5x mol 0.15 mol = 9.167x10 10 M and ph = 9.04 (mole ratio both species are in the same volume)

3 14. Calculate the solubility of Mg(OH)2 in a solution buffered to a ph of KSP = 1.8x10-11 M 3. Mg(OH)2 Mg OH Ksp = [Mg 2+ ][OH ] 2 with ph = 12.0 giving poh = 2.0 and [OH ] = M [Mg 2+ ] = Ksp/[OH ] 2 = 1.8x10-11 M 3 /(0.010) 2 = 1.8x10-7 M = 2x10-7 M 15. Calculate the solubility of LiF in a solution buffered at ph The Ksp of LiF is 1.7x10-3 M 2. The Ka of hydrofluoric acid is 6.8x10-4. Since LiF is a 1:1 salt: s = M = 1.7x10-3 M x x10-3 = x10 3 M Note that s = Ksp is fine at this ph. However at ph = 3: s = M = 1.7x10-3 M x x10-3 = x10 3 M

4 Honors General Chemistry Test 3 Prof. Shattuck, practice Name R = J mol -1 K -1 1 L atm = J T(0 C) = K Answer 8 of the following 10 questions. If you answer more than 8 cross out the ones you wish not to be graded, otherwise only the first 8 will be graded. (6 points each) 1. Is PbBr2 more soluble in : (a) pure water, (b) 0.10 M NaBr, or (c) 0.10 M Pb(NO3)2? 2. Circle the stronger acid in each pair: (a) HF, HBr (b) H3PO4, H3PO3 (c) HClO3, HBrO3 3. Write the reactions that show why CaCO3(s) has increasing solubility with decreasing ph. CaCO3 (s) Ca 2+ (aq) + CO3 2- (aq) with CO3 2- (aq) + H + (aq) HCO3 or CaCO3 (s) H + Ca 2+ (aq) + HCO3 (aq) or CaCO3 (s) + H2O (l) Ca 2+ (aq) + HCO3 (aq) + OH with H + + OH H2O (l) 4. Are aqueous solutions of the following acidic, basic, or neutral? (a) NH4Cl _acidic (b) KNO3 neutral (c) Na2SO4 basic 5. Consider the general reagents at 0.1 M concentration: HCl, H2SO4, NH3, NaOH. Which of these four reagents do you add to get the following precipitates to dissolve? You can use each reagent only once (in other words you will use all four choices). (a). To dissolve Cu(OH)2 (s) add HCl _or H2SO4 (b). To dissolve Zn(OH)2 (s) add NaOH (c). To dissolve AgCl (s) add NH3 (d). To dissolve CaF2 (s) add HCl _or H2SO4 6. In the titration of ammonia with strong acid, is the equivalence point acidic, basic, or neutral? Show the reaction that determines the ph. 7. What are the two conjugate acid base pairs in the reaction: H2PO4 - + H2O H3PO4 + OH base acid acid base Make sure to indicate which in each pair is the acid and which the base. 8. For the following reactions, does the equilibrium position lie to the or right? (a) F + H2O HF + OH (b) HF + H2O F + H3O +

5 9. The volume of an ideal gas is increased from 1.00 L to 5.00 L at a constant pressure of 2.00 atm. Assume q = 0 and calculate the change in internal energy for this process. Remember to convert to J: (not this year) 10. Name the following compounds: Part II. (a) HIO hypoiodous acid (b) H3PO4 phosphoric acid (c) Na2SO3 sodium sulfite 11. Calculate the concentration of Cu 2+ in a solution of M Cu(NH3)4 2+, with an ammonia concentration of 0.20 M. The formation constant is: Cu 2+ (aq) + 4 NH3 (aq) Cu(NH3)4 2+ (aq) Kf = 5.0x Cu(NH3)4 2+ Cu NH3 Kd = 1/Kf = 2.0x10-13 initial change x +x +4x equil x x x Kd = 1/Kf = 2.0x10-13 = [Cu2+ ][NH3] 4 [ Cu(NH3)4 2+ ] = x(0.20+4x) x x(0.20) x = 1.25 x10-13 M 12. Calculate the ph at the equivalence point of a titration of 30.0 ml of M HClO with M NaOH. For HClO, Ka = 1.1x10-8 M. Show the reaction that determines the ph. reaction that determines the ph: ClO HClO + OH equil: x x x Kb = 1x10-14 /1.1x10-8 = 9.09x10-7 = [HClO][OH ] [ClO ] = x x x [OH ] = x = cbkb = (9.09x10-7 ) = 2.13x10-4 and poh = ph = What is the ph of a solution prepared by adding 1.00 L of 0.25 M HCl to 1.00 L of 0.40 M ammonia. For ammonium ion Ka = 5.5x10-10 M. The reaction with strong acid gives: NH3 + H + NH4 + (assume goes to completion) initial 0.40 mol 0.25 mol 0 completion 0.15 mol mol [H + ] Ka ca cb = Ka na nb [H + ] 5.5x mol 0.15 mol = 9.167x10 10 M and ph = 9.04 (mole ratio both species are in the same volume)

6 14. Calculate the solubility of Mg(OH)2 in a solution buffered to a ph of KSP = 1.8x10-11 M 3. Mg(OH)2 Mg OH Ksp = [Mg 2+ ][OH ] 2 with ph = 12.0 giving poh = 2.0 and [OH ] = M [Mg 2+ ] = Ksp/[OH ] 2 = 1.8x10-11 M 3 /(0.010) 2 = 1.8x10-7 M = 2x10-7 M 15. Calculate the solubility of LiF in a solution buffered at ph The Ksp of LiF is 1.7x10-3 M 2. The Ka of hydrofluoric acid is 6.8x10-4. Since LiF is a 1:1 salt: s = M = 1.7x10-3 M x x10-3 = x10 3 M Note that s = Ksp is fine at this ph. However at ph = 3: s = M = 1.7x10-3 M x x10-3 = x10 3 M