You have 100.0 mL of a solution of hydrochloric acid that has a pH of 3.00. You add 100.0 mL of water to this solution. What is the resulting pH of the solution?

3.30

Explanation:

Original volume of the HCl solution = 100.0 mL

pH of the solution = 3.00

Concentration of the hydrogen ions can be calculated as:

pH = - log[H⁺]

So,

3 = - log[H⁺]

[H⁺] = 10⁻³ concentration units.

For original acid solution:

C₁ = 10⁻³, V₁ = 100 mL

For 10% acid solution:

C₂ = ?, V₂ = 200 mL (100 mL of water is added to 100 mL of original solution)

Using

C₁V₁ = C₂V₂

10⁻³*100 = C₂*200

C₂ = 0.5*10⁻³ concentration units.

So,

pH is:

pH = - log[H⁺] = - log (0.5*10⁻³) = 3.30