Medical chemistry and biochemistry
3. Calculations (pH of strong acids and bases, weak acids and bases, buffers)
1. Calculate the pH of the following solutions:
a) 0.045 M HCl
[pH = 1.35]
b) 1 x 10-3 M HNO3 [pH = 3]
c) 0.05 M HClO4
[pH = 1.3]
2. Calculate the pH of the following solutions:
a) 2 x 10-3 M NaOH [pH = 11.3]
b) 0.4 M KOH
[pH = 13.6]
3. Calculate the molarity of a HNO3 solution that has the pH = 2.
[c = 0.01 M]
4. Calculate the pH of a 20 mM H2SO4 solution. Suppose the second ionization of
H2SO4: H2SO4 + 2H2O  2H3O+ + SO42[pH = 1.4]
5. Calculate the pH of a HCl solution that has a weight concentration 2 g/L.
Mr (HCl) = 36.5
[pH = 1.26]
6. What is [OH-] in 1 dm3 of a HCl solution that contains HCl 0.001 moles of HCl?
[ [OH-] = 10-11 mol/L]
7. a) calculate the pH of 0.05 M acetic acid solution. Ka is 1.76 x 10-5 [pH = 3.025]
b) calculate the Ka of a 0.2 M lactic acid solution that has pH = 2.5 [Ka = 5.01 x 10-5]
c) calculate the pH of a 0.002 M NH4OH solution that has pKb = 9.2
[pH = 8.05]
8. 10 mL of HClO4 solution (pH = 2) was diluted with water to the final volume of 100
cm3. Calculate the molarity and pH of this solution.
[c = 0.001 M, pH = 3]
9. 50 mL of a solution contains 4 mg of NaOH. Calculate the pH of this solution.
Mr (NaOH) = 40
[pH = 11.3]
10. 50 cm3 of a 0.2 M NaOH solution was diluted to the final volume of 800 mL. What
is the pH of this solution?
[pH = 12.1]
11. Calculate the pH of a 0.08% NaOH solution. Mr (NaOH) = 40
[pH = 12.3]
12. 25.0 mL of a CH3COOH solution has pH = 3.9. Calculate the weight of CH3COOH
in this solution (in milligrams).
pKa = 4.75, Mr (CH3COOH) = 60
[1.34 mg]
13. Calculate the pH of 0.5% acetic acid solution. Mr (CH3COOH) = 60.05, density =
0.998 g/mL and pK = 4.76
[pH = 2.92]
14. Calculate the pH of a 0.06 M weak bases solutions:
a) NH3 pKb = 4.74
[pH = 11.02]
b) methylamine pKb = 3.43
[pH = 11.67]
c) dimethylamine pKb = 3.27
[pH = 11.75]
15. In 0.1 M HCOOH solution the formic acid is dissociated only in 4%. Calculate the
dissociation constant of formic acid.
[Ka = 1.67 x 10-4]
16. a) pH value of strong base solution changed about 2 units of pH. How many
times the solution was diluted?
[100x diluted]
b) 0.1 M solution of a strong acid was diluted 20 times. What is pH of diluted
solution? [pH = 2.3]
17. What is the pH of a buffer solution that contains 20 ml of 0.05 M NH4Cl and 27
mL of 0.2 M NH4OH? The Kdis of NH4OH is 1.85 x 10-5.
[pH = 10]
18. What is the pH of a buffer solution that contains 60 mL of a 0.2 M acetic acid and
30 mL of a 0.2 M sodium acetate. The pKa of acetic acid is 4.75.
[pH = 4.45]
19. The principal buffer system of blood is a bicarbonate buffer (HCO3- / H2CO3) .
Calculate a ratio of HCO3- / H2CO3 components if the pH is 7.38 and pK(H2CO3) =
6.1.
[19 : 1]
20. A phosphate buffer contains 60 mL of 0.1 M NaH2PO4 and 40 mL of 0.2 M
Na2HPO4. Calculate the pH of this buffer if the dissociation constant of H2PO4- is
6.23 x 10-8.
[pH = 7.33]