Heating to constant mass is a classic 9701 Paper 3 task. By hand, weigh the crucible, spoon in the salt, carry it to the pipe-clay triangle and turn the gas tap. Heat too hard too soon and the solid spits; weigh it hot and the balance drifts. Then work out x in the formula and say what each mistake would do to it. The salt changes from attempt to attempt. Allow about 30 minutes.
Checked: Cambridge 9701 Paper 3, February/March 2023 to May/June 2026. Only the papers in our collection are listed, so the real number may be higher. Question papers are available from Cambridge.
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Every balance reading as shown, to 2 decimal places; a mass of salt in the range asked for; heating repeated until two weighings agree within 0.01 g; masses of residue and water by difference; and an accurate result.
M of the anhydrous salt, the amounts of salt and water, x to at least 2 significant figures, and the whole-number formula.
Why constant mass, the percentage error in a difference of two readings, and the direction each error moves x.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.