Edexcel International A Level (IAL) Chemistry (YCH11) - Unit 1 - 1.11 CORE PRACTICAL 1: Molar volume of a gas-Study Notes - New Syllabus

1.11 Core Practical 1 – Measurement of the Molar Volume of a Gas

Aim

To determine the volume occupied by one mole of carbon dioxide gas by reacting calcium carbonate with ethanoic acid.

Background

The molar volume of any gas at a given temperature and pressure is the same for all gases.

By collecting the carbon dioxide gas produced in a reaction and measuring its volume, the molar volume of the gas can be determined using experimental data.

Overall Reaction

\( \mathrm{CaCO_3(s) + 2CH_3COOH(aq) \rightarrow Ca(CH_3COO)_2(aq) + H_2O(l) + CO_2(g)} \)

Safety

• Wear eye protection.
• Avoid skin contact with ethanoic acid.
• If the delivery tube becomes blocked, remove the bung and clear the blockage before restarting the experiment.
  

Apparatus

• boiling tube or conical flask
• bung with delivery tube
• stand and clamp
• gas syringe or water displacement apparatus
• 100 cm³ and 50 cm³ measuring cylinders
• test tube
• 2 d.p. balance
• \( 1\ \mathrm{mol\ dm^{-3}} \) ethanoic acid
• powdered calcium carbonate

Method

1. Measure \( 30\ \mathrm{cm^3} \) of \( 1\ \mathrm{mol\ dm^{-3}} \) ethanoic acid and place it in a conical flask.
2. Attach the flask to a gas syringe or set up the water displacement apparatus.
3. Weigh a boiling tube containing approximately \( 0.5\ \mathrm{g} \) of calcium carbonate.
4. Add the calcium carbonate to the acid and immediately fit the bung so no gas escapes.
5. Allow the reaction to proceed and record the total volume of carbon dioxide gas produced.
6. Reweigh the empty boiling tube to determine the exact mass of calcium carbonate used.
7. Repeat the experiment several times using increasing masses of calcium carbonate.

Processing Results

The mass of calcium carbonate is converted into moles using:

\( n = \dfrac{m}{M} \)

From the balanced equation, one mole of calcium carbonate produces one mole of carbon dioxide:

\( \mathrm{CaCO_3 : CO_2 = 1 : 1} \)

A graph of volume of CO₂ produced against mass of CaCO₃ used is plotted. The graph should be a straight line through the origin.

From the graph, the volume of carbon dioxide produced by one mole of calcium carbonate can be determined.

Evaluation and Sources of Error

• Gas may escape before the bung is fitted.
• The bung may not be completely airtight.
• Carbon dioxide is slightly soluble in water, which can reduce the measured volume.
• Some gas may escape while adding calcium carbonate.
• Gas syringe plungers may not move freely, affecting readings.