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 have been caused by not all water being removed from the sample during the evaporation process, resulting in an incorrect mass reading.

The error could be avoided by ensuring that the evaporating basin is dried thoroughly before weighing, or by drying the evaporating basin to constant mass.

To calculate X, we can find the mean of the given values:

$X = \frac{0.22 + 0.23 + 0.20}{3} = \frac{0.65}{3} = 0.2167$

Rounding to two decimal places, we find:

X = 0.21 g.

Water sample C has the greatest range of masses of dissolved solids, as the difference between the maximum (0.45 g) and the minimum (0.12 g) is 0.33 g.

To calculate the mass in 1 m³, we first convert 1 m³ to cm³:

$1 ext{ m}^3 = 1 \times 10^6 ext{ cm}^3$

From the sample, 25 cm³ contains 0.016 g of dissolved solids. Therefore, the mass per m³ can be calculated as follows:

$\text{Mass} = \left(\frac{0.016 ext{ g}}{25 ext{ cm}^3}\right) \times 10^6 ext{ cm}^3 = 640 \text{ g}$

In standard form, this is:

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