pH problems

A. Determine the pH of a solution given its hydrogen ion concentration.

The chemical formula for pH is

pH = - log10[H+] where [H+] is the hydrogen ion concentration in moles per litre or M

 

Example: Calculate the pH of a 0.25 M or 0.25 mol L-1 solution.

pH = - log10[H+]

pH = - log10[0.25]

pH = -(-0.60) since log10[0.25] = -0.60

pH = 0.60

 

Calculate the pH of the following solutions of hydrogen ions. Use the pH calculator provided

[H+] concentrations

pH = -0.70

5.0 M
pH = 0.65

0.225 M
pH = -0.30

2.0 M
pH = 0.0

1.0 M
pH = 0.52

0.30 M
pH = 0.30

0.50 M
pH = 1.65

0.0225 M
pH = 0.70

0.20 M
pH = 1.0

0.01 M
pH = 2.52

0.0030 M

 

B. Determine the pH of a strong acid given its concentration.

For strong monoprotic acids like hydrochloric acid HCl and nitric acid HNO3 the concentration of the acid is equal to the concentration of H+ ions.

Example: Calculate the pH of a 0.10 M or 0.10 mol L-1 solution of nitric acid.

HNO3(aq) →H+(aq) + NO3-(aq)
0.10M        0.10M      0.10M

∴ [H+] = 0.10 M

 

pH = - log10[H+]

pH = - log10[0.10]

pH = -(-1.0) since log10[0.10] = -1.0

pH = 1.0

 

However, for diprotic acids like sulfuric acid H2SO4 this is not the case. A diprotic acid produces two moles of hydrogen ions per mole of acid.

Example: Calculate the pH of a 010 M or 0.10 mol L-1 solution of sulfuric acid.

Sulfuric acid is a diprotic acid. When it fully dissociates it produces twice the number of moles of H+ ions.

H2SO4(aq) →2H+(aq) + SO42-(aq)
0.10M         0.20M       0.10M

∴ [H+] = 0.20 M which is twice the concentration of H2SO4

 

pH = - log10[H+]

pH = - log10[0.20]

pH = -(-0.70) since log10[0.20] = -0.70

pH = 0.70

 

Calculate the pH of the following solutions of strongs acids. Use the pH calculator provided

Strong acid concentrations

pH = -1.0

5.0 M H2SO4
pH = 0.19

0.55 M HNO3
pH = -0.46

0.350 M HCl
pH = -0.30

2.0 M HCl
pH = 0.40

0.20 M H2SO4
pH = 0.22

0.60 M HNO3
pH = 1.40

0.0325 M HCl
pH = -0.04

0.550 M H2SO4
pH = 0.0

1.0 M HNO3
pH = 2.10

0.0040 M H2SO4

Molar Mass
 

Formula Calculator