A student carried out a flame test on a sample of solid potassium chloride - Edexcel - GCSE Chemistry - Question 10 - 2023 - Paper 2

A clean wooden splint would provide accurate observations, as it would only allow reactions from the potassium chloride sample and not from residual impurities.

The student should have seen a lilac color in the flame if the test was conducted correctly, indicating the presence of potassium ions.

To test for chloride ions, dilute nitric acid is added to the sample, followed by a few drops of silver nitrate solution. A white precipitate of silver chloride will form if chloride ions are present.

To find the mass of barium chloride needed, we can use the formula:

$ext{mass} = ext{concentration} imes ext{volume}$

Here: Concentration = 83 g/dm³ and Volume = 25 cm³ (which is 0.025 dm³).

Thus,

$ext{mass} = 83 imes 0.025 = 2.075 ext{ g}$

Rounded to 2 significant figures, the mass is 2.1 g.

The ionic equation for the reaction between barium chloride and aluminium sulfate leading to the formation of a precipitate can be written as:

$3 ext{Ba}^{2+}(aq) + 3 ext{SO}_4^{2-}(aq) + 2 ext{Al}^{3+}(aq) + 6 ext{Cl}^-(aq) \rightarrow 3 ext{BaSO}_4(s) + 2 ext{AlCl}_3(aq)$