Collecting a gas over water is a regular 9701 Paper 3 Question 1. By hand, weigh the bottle of carbonate, fill a 250 cm³ measuring cylinder to the brim and turn it upside down in the trough, tip the powder into the acid and get the bung back in before the gas escapes. Then read the upside-down scale, work out Mr and Ar, name the metal and evaluate the method. The carbonate 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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A heading with its unit for every row, both balance readings as the balance shows them with the mass added by difference, the gas volume as a whole number of cm³ read at the bottom of the meniscus, and two accuracy marks for a volume per gram close to the value from perfect technique.
Amount of CO2 from the molar volume at room conditions, the equation with state symbols, the 1 : 1 ratio and Mr to 2 to 4 significant figures, Ar = Mr − 60.0 with the metal identified, and the percentage difference from the true Ar.
Percentage errors in the mass (two balance readings) and the volume (one cylinder reading), why the acid is in excess, which way dissolved CO2 moves Ar, and improvements for the bung delay and for gas dissolving.
The marking follows the conventions in published Cambridge mark schemes. The experiments, readings and wording on this page are our own.