Calculate the number of moles of HCl in 200 cm3 of a 1.5 mol dm⁻³ solution.

There are 1000 cm$^3$ in 1 dm$^3$.

$$\text{Volume} = 200 \text{ cm}^3 \times \frac{1 \text{ dm}^3}{1000 \text{ cm}^3} = 0.200 \text{ dm}^3$$

$$\text{Moles} = \text{Concentration} \times \text{Volume}$$

Given concentration = $1.5 \text{ mol dm}^{-3}$
Given volume = $0.200 \text{ dm}^3$

$$\text{Moles of HCl} = 1.5 \text{ mol dm}^{-3} \times 0.200 \text{ dm}^3$$ $$\text{Moles of HCl} = 0.30 \text{ mol}$$

The number of moles of acid present is $\text{0.30 mol}$.