Core practical 1- measure the molar volume of a gas

Write a chemical equation for the reaction between ethanoic acid, CH₃COOH and calcium carbonate.

CaCO₃ + 2CH₃COOH → Ca(CH₃COO)² + CO₂ + H₂O

Why is it more accurate to find the mass of the calcium carbonate used by weighing the test tube with calcium carbonate in, then tipping it out and reweighing the test tube, rather than weighing the empty tube at the start?

Allows for the mass of any calcium carbonate that remains in the test tube after tipping it out.

Identify the major source of error caused by the procedure used

Gas loss before replacing the bung.

What change to the procedure/apparatus could be made to eradicate this error?

Use the tube containing the acid inside the vessel containing the calcium carbonate – tip to mix the reagent.

Carry out two calculations to show that the ethanoic acid was in excess in all experimental runs.

When 0.40g of calcium carbonate is used:

moles CaCO3 = 0.4/100.1 = 0.003996

moles ethanoic acid = c × v = 1 × 30/1000 = 0.03 moles

acid > 2 × moles calcium carbonate – hence ethanoic acid in excess.