A student investigated the mass of dissolved solids in four water samples A, B, C and D - AQA - GCSE Chemistry Combined Science - Question 4 - 2020 - Paper 2

The error could be caused by not all water being removed from the evaporating basin after boiling, leading to a mass that includes both dissolved solids and residual water.

To avoid this error, ensure the basin is heated to constant mass so that all water has evaporated. Additionally, drying the bottom of the basin thoroughly before recording the mass will help eliminate any residual water.

To calculate X, we find the mean of the three recorded measurements for water sample A:

$X = \frac{0.22 + 0.23 + 0.20}{3} = 0.21 \text{ g}$

So, X = 0.21 g.

Water sample C has the greatest range of masses of dissolved solids, with maximum value 0.50 g and minimum value 0.42 g, leading to a range of 0.08 g.

To calculate the mass of dissolved solids in 1 m³:

1 m³ = 1 × 10³ cm³

Using the provided concentration of dissolved solids:

$\text{Mass} = \frac{1 \text{ m}^3}{25 \text{ cm}^3} \times 0.016 \text{ g} \approx 640 \text{ g}$

Thus, in standard form, the answer is:

Mass = $6.4 \times 10^2$ g.