Problems -- Chapter 1 1. Write balanced chemical equations for the important equilibrium that is occurring in an aqueous solution of the following. (a) NaNO and HNO answers: see end of problem set (b) NaHCO 3 and H CO 3 (c) HClO and KClO (d) RbF and HF (e) KCl and HCl (f) H 3 PO and KH PO (g) (CH 3 ) NH NO 3 and (CH 3 ) NH. Write the appropriate equilibrium constant expressions (K a, etc.) for each of the the solutions above. 3. Determine the ph of a mixture of 0.100 M solutions of the two components in part (a) above (Ka =.5 x 10 - ) Answer: ph = 3.35. Write the appropriate reactions (see end of this document for answers) and calculate the ph of the following: (a) 0.35 M NaIO/0.0M HIO (Ka = 5.x10-9 ) (b) 0.8 M NaIO/0.78 M HIO (Ka =.0x10-11 ) (c) 0.0 M NH3 (Kb = 1.8x10-5 )/0.55 M NHCl. Answers: (a) 8.9 (b) 10.9 (c) 9.1 5. HNO is a weak acid whose K a =.5x10 -. How many grams of NaNO would have to be added to 50 ml of a 0.M HNO acid solution to give a buffer of ph =.00. (3. g). A 0.5-gram sample of an unknown weak acid (call it HA for short) is dissolved in enough water to make 5.0 ml of solution. This weak acid solution is then titrated with 0.100 M NaOH and 5.0 ml of the NaOH solution is required to reach the equivalence point. Using a ph meter, the ph of the solution at the equivalence point is found to be 8.5. Note: writing balanced reactions will solve this problem! (a) Determine the molecular mass of the unknown acid. 138.9 g/mole (b) Determine the pk a value of the unknown acid. 3.9 7. The pk b value for ammonia (NH 3 ) is.7. Calculate the mass (in grams) of solid ammonium chloride (NH Cl, formula mass = 53.5 g/mole) that must be added to 300 ml of 0.5 M NH 3 solution to make a buffer solution with a ph equal to 10.00. Like the problems done in class write ALL balanced reactions whether they go essentially to completion or they are at equilibrium. Use the correct arrows. 0.73 g 8. A 50 ml portion of a 0.10 M solution of a weak acid, HA, whose Ka equals 1.0 x 10 -, is diluted to 50 ml and then titrated with 0.10 M NaOH. Calculate ph after the following ml of the NaOH solution have been added. Like the problems done in class write ALL balanced reactions whether they go essentially to completion or they are at equilibrium. Use the correct arrows. (a) 0 (b) 5 (c) 5 (d) 50 (e) 0
(a).85 (b) 3.05 (c).00 (d) 8.11 (e) 11.51 9. Fifty ml of 0.1 M NH3 is titrated with 0.10 M HCl. The Kb of the weak base NH3 is 1.8 x 10-5. Calculate the ph after the following ml of the HCl solution have been added. Like the problems done in class write ALL balanced reactions whether they go essentially to completion or they are at equilibrium. Use the correct arrows. (a) 0 (b) 10 (c) 5 (d) 50 (e) 55 (a) 11.13 ( b) 9.8 (c) 9. (d) 5.8 (e).3 10. Shown on the next page is the titration curve for the titration of 50.00 ml of a solution of the monoprotic acid, HA, with 0.01 M NaOH. What is the molarity of the acid?(show reaction and yoru work) Is the acid a weak acid or a strong one? If it is a weak acid, what is the value of Ka? (0.0 M, weak, Ka=.8 x 10 - ) 1 Titration of 50.00 ml of HA with 0.01M NaOH 10 8 ph 0 0 0 0 80 100 ml NaOH 10 10 10 11. Shown below is the titration curve for the titration of 50.0 ml of a solution of the weak ammoniatype base, methyl amine, CH3NH, with 0.01M HCl. What is the molarity of the base? (show reaction and your work) What is the value of Kb for methyl amine? (0.0 M answer given; K b = 3.x10 - )
1 3 10 ph 8 0 50 100 150 ml 0.01M HCl 1. Consider reactions involving the following acids and bases. State in each case whether the ph at the equivalence point would be below 7, at 7, or above 7. (a) acid = HClO base = KOH (b) acid = HNO3 base = NH3 (c) acid = HF base = LiOH (a) 7 (b) <7 (c) >7 13. A 3.0 ml sample of a 0.0 M HNO 3 solution was titrated with 0.8 M KOH. Calculate the ph after the following volumes of KOH have been added: Like the problems done in class write ALL reactions whether they go essentially to completion or they are at equilibrium. Use the correct arrows. (a) 0 ml (b) 10.0 ml (c) 0.0 ml (30.0 ml (e) 0.0 ml ( f) 50.0 ml. (a) 0.0 (b) 0.8 (c) 1.07 d) 7.00 (e) 1.80 (f) 13.05 1. Calculate the ph s of the following: Like the problems done in class write ALL reactions whether they go essentially to completion or they are at equilibrium. Use the correct arrows. Note, that you will need TWO reactions in some cases! THINK! (a) the solution formed by mixing 0.0 ml of a 0.30M HCl solution with 1 ml of a 0.5 M NaOH. (b) the solution formed by mixing 18.0 ml of a 0.M HC H 7 O solution with 10.0 ml of a 0.35M NaOH (K a for HC H 7 O = 8.0x10 5 ) (c) the solution formed by mixing 15.0 ml of a 0.7M HF with 0.0 ml of a 0.0M KOH solution (K a for HF = 7.1x10 ) (d) the solution formed by mixing 30.0 ml of a 0.0 M HCHO solution with.0 ml of a 0.0 M KOH solution (K a for HCHO = 1.7x10 ) (e) the solution formed by dissolving.85 g of KF in 10 ml of a 0.30 M HF solution (K a for HF = 7.1x10 ) (f) the end point of the titration of 58.0 ml of a 0.8 M HCHO with 0.0 M KOH. (a) 1.03 (b) 3.9 (c) 3.7 (d) 1.73 (e) 3.8 (f) 8.55
15. A 0.0 ml sample of a 0.0 M HNO solution was titrated with 0.80 M KOH. Given that HNO is a weak acid whose K a =.5x10 -, calculate the ph after the following volumes of KOH have been added: Like the problems done in class write ALL reactions whether they go essentially to completion or they are at equilibrium. Use the correct arrows. (a) 0 ml; (b) 5.0 ml; (c) 10.0 ml; (d) 0.0 ml; (e) 30.0 ml; (f) 0.0 ml (a) 1.87 (b).87 (c) 3.35 (d) 8.39 (e) 13.0 (f) 13.30 1. Drawn below is a plot of ph vs ml of 0.0 M NaOH for the titration of 50.0 ml of a weak diprotic acid. What is the concentration of the acid? What are the values of Ka1 and Ka for the acid? Write the reaction that is occurring for each equivalence point. (Answer: 0.80M, Ka1 = 5.0x10-3, Ka =.3x10-8 ) 1 1 10 ph 8 0 0 50 100 150 00 50 300 350 00 ml 0.M NaOH 17. The Ksp of Pb(IO3) at 5 C = 3. x 10-13. What is the solubility of Pb(IO3) in moles per liter and in grams per liter? Write the reaction. (.3 x 10-5 mol/l ; g/l = 0.0) 18. Calculate the Ksp of the following compounds. The solubilities are given in moles per liter. Write the reaction. (a) Mg(OH) = 1.3 x 10 - M (8.8 x 10-1 ) (b) AgCO = 1. x 10 - M (1.1 x 10-11 ) 19. Calculate the Ksp of the following salts. Solubilities are given in grams/liter. Write the reaction. (a) BaCrO =.3 x 10- -3 g/l (8.3 x 10-11 ) (b) CaF =.7 x 10 - g/l (1.7 x 10-10 ) 0. What [SO - ] must be exceeded to produce a RaSO precipitate in 500 ml of a solution containing 0.00010 moles of Ra +? (Ksp = x 10-11 ). Write the reaction. ( x 10-7 M) 1. A solution contains an Mg + concentration of 0.001 mole/liter. Will Mg(OH) (Ksp = 8.9 x 10-1 ) precipitate if the OH - concentration of the solution is Write the reaction. (a) 10-5 mole/liter? (b) 10 - mole/liter? (a) Q = 1x10-13, no (b) Q = 1x10-11, yes]. How many grams of NaOH are required to start the precipitation of Mg(OH) in 100 ml of a solution which contains 0.1 g of MgCl? Write the reaction. (1.1 x 10 - g)
3. The value of Ksp for PbCl is 1. x 10-5. Will a precipitate of PbCl form when the following solutions are mixed? Write the reaction. 5 (a) 100 ml of 0.01 M Pb(NO3) and 100 ml of 0.00 M NaCl. (b) 10 ml of 0.01 M Pb(NO3) and 30 ml of 0. M NaCl. (c) 10 ml of 0.01 M Pb(NO3) and 0 ml of 0.0 M NaCl. (d) 10 ml of 0.01 M Pb(NO3) and 0 ml of 0.0 M CaCl. (a) no, Q = 5x10 9 (b) yes, Q= 5.x10 5 (c) no, Q= 5.3x10 (d) yes, Q=.1x10 5. Silver chromate, Ag CrO, is an "insoluble" substance with a K sp value of 1. x 10-1. Silver ion forms a stable complex ion with cyanide ion that has the formula Ag(CN) - and a formation constant (K f ) of 5.3 x 10 18. Calculate the molar solubility of Ag CrO in each of the following solutions. Write balanced chemical equations for any important equilibrium reactions that are occurring. (a) in water.9 x 10-5 M (b) in.00 M Na CrO 3.87 x 10-7 M (c).00 M NaCN 0.50 M 5. A saturated solution of Mg 3 (PO ) has a concentration of 0.939 mg per liter. Calculate the solubility product constant for Mg 3 (PO )..7 x 10 -. Cadmium carbonate, CdCO3, is a sparingly soluble salt whose Ksp=.5x10-1. It is also known that Cd + forms the [Cd(NH3)] + complex ion that has a formation constant, Kf = 1.0x10 7. (a) Calculate the molar solubility of CdCO3 in.0m NH3. (0.018 mol/l) (b) What NH3 concentration would be required to dissolve.00 mmol of CdCO3 in one liter of the solution? (.83 M)
Answers to #1 (a) HNO H + + NO - (b) H CO 3 HCO - 3 + H + (c) HClO H + + ClO - (d) HF F - + H + (e) not a buffer: the only equilibrium in this neutral solutions is dissociation of water, i.e., H O H + + OH - (f) H 3 PO H + + H PO - (g) (CH 3 ) NH + H + + (CH 3 ) NH. NOTE: ION CHARGES ARE CRITICALLY IMPORTANT! a. Buffer: HIO H + + IO - K a applies or IO - + H O OH - + HIO K b applies b. Buffer: HIO H + + IO - K a applies or IO - + H O OH - + HIO K b applies c. Buffer: NH + H + + NH 3 K a applies or NH 3 + H O NH + + OH - K b applies 5. HNO H + + NO - use K a. a. reaction is critically important: HA + NaOH NaA + NaCl (note the direction of the arrow: REXN is COMPLETE, not an equilibrium b. What is in the beaker at the equivalence point? By now you should be able to write this reaction! THINK befor you look at the answer! A - + H O HA + OH -