University of Texas, Arlington

CHEM 1442

Chapter 16 Questions

pH of Buffer Solutions

1)200 ml of 0.1 M HF and 300 ml of 0.1 NaF are mixed. What is the pH of the solution?  Ka = 7.2 X 10^-4 (3.3)

                             2.               0.02 mole of NH₃ and 0.03 mole of NH₄Cl are mixed in 300 ml.

What is the pH of the solution? Kb = 1.8 X 10^-5 (9.1)

Buffering Action

 

                             3.               0.01 mole of HCl is added to 1 liter of a buffer which contains 0.02 mole of NH₃ and 0.03 mole of NH₄Cl. What is the pH of the solution after all are mixed? (Kb NH₃ = 1.8 X 10^-5) (8.65)

 

                             4.               0.040 mole of NaOH is added to a buffer containing 0.05 mole of CH₃COOH and 0.07 mole of CH₃COONa in 300 ml. What is the pH of the mixture. Ka CH₃COOH = 1.8 X 10^-5 (5.8)

 

                             5.               0.05 mole of HCl is added to a liter of buffer containing 0.04 mole of NH₃ and 0.03 mole of NH₄Cl. What is the pH? Kb = 1.8 X 10^-5

(2)

 

Titration Problems

 

                             6.               30 ml of 0.1 M NaOH is added to 28 ml of 0.10 M HCl. What is the pH? (11.5)

                             7.               30 ml of 0.20 M NH₃ and 25 ml of 0.20 HCl are mixed. What is the pH?                      Kb NH₃ = 1.8 X 10^-5 (8.6)

 

Calculating Ksp and Molar Solubility

 

                           8.        The molar solubility of PbBr2 is 1.0 X 10-2 mole/L. What is the Ksp?

                           9. BaSO4 is shaken in water and after a period of time the concentration of Ba²⁺ is found to be 1.04 X 10^-5. What is Ksp for BaSO₄?

 

Calculate the Solubility of Salts in a Common Ion Solution

 

                           10.     Ksp for BaSO4 is 1.0 X 10-10. What is the molar solubility of BaSO4 in a 0.02 M Na2SO4 solution?

                           11.     Ksp for AgCl is 1 X 10-10. What is the molar solubility of AgCl in a solution which is 0.05 M in KCl?

 

Using Q (Reaction Quotient) Determine if a Precipitate Will Form

 

                           12.     Ksp for AgI = 1.5 X 10-16. If 200 ml of 0.03 M NaI and 400 ml of

0.04 M AgNO3 are mixed, will a precipitate of AgI form. ( In the first

                                      blank put the value of Q. In the second blank answer yes or no.)

 

                           13.     Ksp for Pb(OH)2 is 2.8 X 10-16. If 300 ml of 0.02 M Pb(NO3)2 and 500 ml of 0.10 M NH3 are mixed, will a precipitate form. (In the first

                                      blank put the value of Q. In the second blank answer yes or no.)

( Kb for NH₃ = 1.8 X 10^-5)

Changes in Solubility

 

14. The following are placed in water and .01 M HCl. In which will they be more soluble? Or will they be the same?
    1. PbCl₂ (b) Cu(NO₃)₂          (c) Cu(OH)₂ (d) Ag NO₃

 

Acid and Base Definitions

 

15. Which can be a Bronsted/Lowry base but not Arrhenius?
    1. NaOH (b) KOH (c) NH₃ (d) Cu(OH)₂
16. NH₃ + BH₃ → NH₃BH₃ Which species is the Lewis Acid?
17. HCl + H₂O → H₃O⁺ + Cl^- Identify the acid, base, conjugate acid, and conjugate base
18. In the following two groups, select the strongest acid. Group 1: HClO, HClO₂, HClO₃

Group 2: HClO, HBrO, HIO

Titration Curves

19. Answer 7, greater than 7, or less than 7
    1. the equivalence point of a titration of HCl and NaOH
    2. the equivalence point of a titration of HCl and NH₃
    3. the equivalence point of a titration of HF and NaOH

 

20. Which equation below best describes the reaction that occurs when 0.01 mol HCl(g) is added to a 1.0 L solution containing 0.10 M nitrous acid (HNO₂) and 0.10 M sodium nitrite (NaNO₂)?

 

1.  

2

HNO₂(aq) + H₂O(l) ? NO ^–(aq) + H₃O⁺(aq)

2.  

2

HNO₂(aq) + H₂O(l) ?            NO ^–(aq) + H₃O⁺(aq)

3.  

2

HNO₂(aq) + OH^–(aq) ? NO ^–(aq) + H₂O(l)

4. HCl(aq) + HNO₂(aq) ? ClNO(aq) + H₂O(l)
5.  

2

H₃O⁺(aq) + NO ^–(aq) ? HNO₂(aq) + H₂O(l)

21.   Which of the following will give a buffer solution when equal volumes of the two solutions are mixed? ( I ) 0.10 M HNO₃ and 0.10 M NaNO₃ ( II ) 0.10 M HC₂H₃O₂ and 0.10 M NaC₂H₃O₂

( III ) 0.10 M HC₂H₃O₂ and 0.20 M NaOH (IV)0.10 M HNO₃ and 0.20 M NaC₂H₃O₂

 

22. Which of the salts below will become more soluble as the pH is lowered? ( I ) Ag₂CO₃ (II) PbCl₂ (III) MgF₂
    1. none of these (b) I  (c) I and III (d) III (e) I, II, and III

 

23. Polyprotic Acids: Write out the three reactions for H₃PO₄. Arrange in order from strongest to weakest acid: H₃PO₄, H₂PO₄^-, HPO₄^2-.
24. What is the conjugate base of each of the following: HCl, HNO₂, and CH₃COOH? Which is the weakest conjugate base?

pH of a Buffer Solution

25. How many moles of NH₄Cl must be added to 2 L of 0.1 M NH₃ to form a buffer whose pH is 9.00?