pH Calculation after mixing acid and base

Calculate the pH of the resultant solution when solutions of acids and/or bases are diluted or mixed

Mixing acids and Bases

Example 1

Calculate the pH after 30 mL of 0.10 mol L^–1 sodium hydroxide is added to 50 mL of 0.30mol L^–1 hydrochloric acid solution. Include a balanced equation in your answer.

$$HCl (aq) + NaOH(aq) \rightarrow NaCl(aq)+ H_2O(l)$$

Moles of NaOH added =

$$n = cV = 0.10 \times 0.030 = 0.0030 mol$$

Moles of HCl present =

$$n = cV = 0.30 \times 0.050 = 0.015 mol$$

Since 1 mol HCl reacts with 1 mol NaOH, then all the NaOH will be neutralised by the HCl

Mol NaOH remaining =

$$0.015 - 0.0030 = 0.012mol$$

Volume solution =

$$30 + 50 = 80mL$$

Remaining [HCl] =

$$\frac{0.012}{0.08} = 0.15M$$

Since HCl is a strong acid, [H⁺] = [HCl] = 0.15 M

pH = -log(0.15) = 0.82 (2 s. f.)