SOLUTION AND ACID & BASE
EQUILIBRIUM PROBLEMS
You may need to refer to the Handbook of Chemistry and Physics for some data.
1. Calculate the pH of a solution prepared from 0.14 mole of formic acid (HCOOH) and enough water to make 1.0 liter of solution. Ka = 1.77 x 10 4
2. Calculate the pH and the pOH of a solution prepared from 0.25 mole of NH4Cl and enough water to make one liter of solution. Ka = 5.59 x 1010 for the ammonium ion.
3. A solution prepared from 0.13 mole of an organic acid and enough water to form one liter of solution is found to have a pH of 5.45. Calculate the Ka of the acid. Can you identify it?
4. The pH of a 1.00 M solution of urea, a weak organic base, is 7.050. Calculate the Ka of protonated urea.
5. Calculate the amount of sodium acetate that must be dissolved in 0.25 liter of water to produce a solution of pH = 8.90. Ka (acetic acid) = 1.76 x 105
6. Calculate the pH at the equivalence point on the titration of 0.20 M acetic acid solution with 0.20 M sodium hydroxide solution. Ka (HAc) = 1.76 x 105
7. Calculate the quantity of sodium acetate that must be dissolved in 1.0 liter of a 1.4 M acetic acid solution to prepare a buffer of pH = 4.36. Assume no volume changes.
Ka = you should know by now.
8. Calculate the pH of 1.0 liter of a buffer solution prepared from 1.0 mole of lactic acid and 1.0 mole of sodium lactate before and after the addition of 0.10 mole of HCl. The Ka for lactic acid is 1.37 x 10 4
9. Repeat the calculation of #8 for a buffer solution prepared from 0.10 mole of each component. Discuss your result in terms of buffer capacity.
10. The formula of oxalic acid can be written as H2C2O4. Both protons are acidic. Calculate the concentration of all species at equilibrium in a solution prepared from 0.75 mole of oxalic acid and enough water to make one liter of solution. Oxalic acid ionization constants are: Ka1 = 5.36 x 102 Ka2 = 5.42 x 105
11. A solution is 0.30 M in HCl and a 0.20 mole amount of H2S (g) is dissolved in the solution. Calculate the sulfide ion concentration at equilibrium. Ka1 = 1.1 x 10 7 Ka2 = 1.0 x 10 12
12. Calculate the solubility of Au(OH)3 in neutral solution. The Ksp is 5.5 x 10 46 .
(HINT: pOH = 7. Consider the common ion effect.) Would you expect its solubility to be different if dissolved in an acidic or basic solution? Explain.
13. Consider the following gaseous reaction: CO + H2O = CO2 + H2
At equilibrium the concentrations of CO, H2O, CO2 and H2 are 0.01, 0.02, 0.012 and 0.012 mole/liter respectively. Now enough CO is added to raise its concentration temporarily to 0.02 and enough H2 is added to temporarily raise its concentration to 0.02 also. Does reaction occur? If so, determine the equilibrium concentrations of all species when the new equilibrium is reached.
14. A buffer is made by mixing 500 ml of 0.80 M NH3 with 500 ml of 0.80 M NH4Cl. Find the pH of the buffer. Find the pH after adding 0.02 mole of HCl. Find the pH after adding 0.02 mole of NaOH to the original buffer. Find the pH after adding 0.5 mole of HCl to the original buffer. The Kb(NH3) = 1.8 x 105 Ka(NH4+ ) = 5.6 x 1010
15. What is the pH of the solution obtained by titrating 1.24 g of benzoic acid dissolved in 50.0 ml of water with 0.180 M NaOH until the equivalence point is reached? You'll need to find K values. Neglect any change in volume due to benzoic acid. Assume volumes are additive. Also, pick a suitable indicator for this titration.
16. Calculate the pH of a solution obtained by mixing 500.0 ml of 0.10 M NH3 with 200.0 ml of 0.15 M HCl.
17. A 0.050 M aqueous solution of sodium hydrogen sulfate, NaHSO4, has a pH of 1.73. Calculate Ka2 for sulfuric acid. Since sulfuric acid is a strong electrolyte, you can neglect hydrolysis of the HSO4 ion.
18. Compare the acid ionization constant of HCO3 with its base ionization (hydrolysis) constant. Which is more likely for bicarbonate; acid ionization or hydrolysis? What is the pH of a 0.10 M solution of sodium bicarbonate, NaHCO3?
19. Aspirin (acetylsalicylic acid) was first marketed in 1899 to control fever and the pain of headache. What is the pH of a saturated solution of aspirin (0.019 M)? Ka = 3.3 x 10 4
20. Oxalic acid, HOOCCOOH, is found in a wide variety of plants (rhubarb, spinach) usually as salts. What is the pH of a 0.50 M aqueous solution of oxalic acid? What is the concentration of oxalate ion, OOCCOO ? (See #10 above for data.)
21. The pH of a white vinegar solution is 2.45. This vinegar is an aqueous solution of acetic acid with a density of 1.09 g/ml. What is the mass percent of acetic acid in the solution?
22. Determine the molality, m, of the solution in #21 with respect to all aqueous species present. i.e. HAc, H+, and Ac- considered as one solute.
23. Determine the freezing point of vinegar (#21) based on the data collected and information determined above.
24. Could you do the reverse of this calculation? i.e. knowing the FP, calculate the pH?