A student is provided with 5.00 cm³ of 1.00 mol dm⁻³ ammonia solution - AQA - A-Level Chemistry - Question 30 - 2017 - Paper 3

To find the total volume needed to achieve a concentration of 0.050 mol dm⁻³ with 0.005 moles of ammonia, we can use the formula:

$\text{volume} = \frac{\text{moles}}{\text{concentration}}$

Substituting the values:

$\text{volume} = \frac{0.005 \text{ moles}}{0.050 \text{ mol dm}^{-3}} = 0.1 \text{ dm}^3 = 100 \text{ cm}^3$

The volume of water to be added is the difference between the total volume required and the initial volume of the ammonia solution:

$\text{volume of water} = \text{total volume} - \text{initial volume}$

Substituting the values:

$\text{volume of water} = 100 \text{ cm}^3 - 5.00 \text{ cm}^3 = 95.0 \text{ cm}^3$