2. Steps for Calculating pH of Strong Acids

Example: 0.1 $mol·dm⁻³ HCl$ Solution

1. Write the ionisation equation: $−HCl \rightarrow H^+ + Cl^-$

2. Determine $[H_3O^+]:$

• Since $HCl$ fully ionises, $[H₃O⁺] = 0.1$ $mol·dm⁻³.$

3. Calculate $pH$: $\text{pH} = -\log(0.1) = :success[1]$

3. Steps for Calculating pH of Strong Bases

Example: 0.5 $mol·dm⁻³ NaOH$ Solution

1. Write the dissociation equation: $NaOH \rightarrow Na^+ + OH^-$

2. Determine $[OH^-]:$

• Since NaOH fully ionises, $[OH⁻] = 0.5$ $mol·dm⁻³.$

3. Calculate $pOH$: $\text{pOH} = -\log(0.5) = :highlight[0.3]$

4. Convert to pH: $\text{pH} = 14 - 0.3 = :success[13.7]$

4. Worked Example

Find the $pH$ of a 0.6 $mol·dm⁻³ H₂SO₄$ solution

1. Step 1: Ionisation reaction: $H_2SO_4 + 2H_2O \rightarrow 2H_3O^+ + SO_4^{2-}$

2. Step 2: Find the mol ratio of acid to H₃O⁺:

• 1 mol H₂SO₄ → 2 mol H₃O⁺

3. Step 3: Calculate [H3O+][H₃O^+]: $[H_3O^+] = 0.6 \times 2 = :highlight[1.2]$ ${ mol·dm}^{-3}$

4. Step 4: Calculate pH: $\text{pH} = -\log(1.2) = :success[0.08]$