3. Worked Example 1

Problem:

A $20$ $cm³$ sample of diluted $H₂SO₄$ is titrated with $25$ $cm³$ of $NaOH.$

The concentration of $H₂SO₄$ is $0.15$ $mol·dm⁻³.$

Calculate the concentration of $NaOH.$

Step 1: Write the Balanced Equation

$H_2SO_4 + 2NaOH → Na_2SO_4 + 2H_2O$

Mole ratio: $H₂SO₄ : NaOH = 1 : 2$

Step 2: Apply the Titration Formula

$\frac{1}{2} = \frac{(0.15)(0.02)}{c_b (0.025)}$

$c_b = \frac{(0.15)(0.02) \times 2}{0.025}$

cb=0.8 mol\cdotpdm⁻³

Thus, the concentration of $NaOH$ is 0.8 mol·dm⁻³.

4. Worked Example 2

Problem:

$8 g$ of $NaOH$ is dissolved in $350 cm³$ of water. $15$ $cm³$ of this solution neutralises $20$ $cm³$ of $H₂SO₄.$

Find the concentration of H₂SO₄.

Step 1: Find NaOH Concentration

$Molar mass of NaOH=40 g$\cdotp$mol⁻¹$

$n = \frac{8}{40} = 0.2 \text{ mol}$

$c = \frac{0.2}{0.35} = 0.57$ $mol$\cdotp·$dm⁻³$

Step 2: Use Titration Formula

$\frac{2}{1} = \frac{(0.57)(0.015)}{c_a(0.02)}$

$c_a = \frac{(0.57)(0.015)}{2(0.02)}$

$ca=0.36 mol$\cdotp$dm⁻³$

Thus, the concentration of $H₂SO₄$ is 0.36 mol·dm⁻³.