Potassium alum is a hydrated salt containing aluminium ions, potassium ions and sulfate ions. 1 mol of hydrated potassium alum contains 12 mol of water of crystallisation. Hydrated potassium alum decomposes when heated, losing its water of crystallisation and becoming anhydrous. You will determine the formula of potassium alum by heating the hydrated salt until it becomes anhydrous. FA 1 is hydrated potassium alum. - Weigh a crucible with its lid. Record the mass in the space for results. - Add all of the FA 1 to the crucible. - Weigh the crucible and lid with FA 1. Record the mass. - Calculate and record the mass of FA 1 added. - Place the crucible on the pipe-clay triangle. Heat the crucible and contents gently for approximately 2 minutes with the lid on. - Remove the lid. Heat the crucible and contents strongly for approximately 5 minutes. - Replace the lid and leave the crucible and residue to cool for at least 5 minutes.

Chemistry

IGCSE&ALevel

CAIE

Exam No：9701_m25_qp_33 Year：2025 Question No：1(a)

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2.2.1 define and use the term mole in terms of the Avogadro constant

2.3.1.1 the prediction of ionic charge from the position of an element in the Periodic Table

2.3.1.2 recall of the names and formulae for the following ions:

2.3.2 write and construct equations (which should be balanced), including ionic equations (which should not include spectator ions)

2.3.3 use appropriate state symbols in equations

2.3.4 define and use the terms empirical and molecular formula

2.3.5 understand and use the terms anhydrous, hydrated and water of crystallisation calculate empirical and molecular formulae, using given data

2.4.1.1 reacting masses (from formulae and equations) including percentage yield calculations

2.4.1.2 volumes of gases (e.g. in the burning of hydrocarbons)

2.4.1.3 volumes and concentrations of solutions

2.4.1.4 limiting reagent and excess reagent (When performing calculations, candidates’ answers should reflect the number of significant figures given or asked for in the question. When rounding up or down, candidates should ensure that significant figures are neither lost unnecessarily nor used beyond what is justified (see also Mathematical requirements section).) deduce stoichiometric relationships from calculations such as those in 2.4.1 (1)–(4)

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