Could anyone post a sample answer paper (like a response from a student) to a chemistry practical exam? The way we should draw the tables and organize data wasn't clear from the mark schemes. Here's a sample question........
HOW DO YOU TACKLE IT?!!!
2 Read through the question before starting any practical work.
The percentage purity of the sodium carbonate can also be determined by measuring the
temperature change when a weighed sample of the solid carbonate reacts with an excess of
hydrochloric acid and the following information is used.
Na2CO3(s) + 2HCl(aq) → 2NaCl(aq) + CO2(g) + H2O(l) ΔH = –37.0 kJ mol–1
You are provided with the following.
FA 4, impure solid sodium carbonate
FA 5, 2.0 mol dm–3 hydrochloric acid
Measurement of temperature change
(a) Follow the instructions below to determine the percentage purity of the sodium
carbonate.
You will carry out the experiment twice.
• Weigh the empty weighing bottle.
• Reweigh the bottle with between 4.00 g and 4.50 g of FA 4.
• Support the plastic cup in the 250 cm3 beaker and add to it, from a measuring
cylinder, 50 cm3 of FA 5.
• Measure and record the steady temperature of the FA 5 in the plastic cup.
• Add the FA 4 from the weighing bottle to the plastic cup, a little at a time to
prevent acid spray. Stir and record the highest temperature reached.
• Reweigh the empty weighing bottle.
In an appropriate format in the space below, record
• all measurements of mass and temperature,
• the mass of FA 4 used, m,
• the temperature rise, ΔT.
Empty and rinse the plastic cup.
Repeat the experiment.
Results
HOW DO YOU TACKLE IT?!!!
2 Read through the question before starting any practical work.
The percentage purity of the sodium carbonate can also be determined by measuring the
temperature change when a weighed sample of the solid carbonate reacts with an excess of
hydrochloric acid and the following information is used.
Na2CO3(s) + 2HCl(aq) → 2NaCl(aq) + CO2(g) + H2O(l) ΔH = –37.0 kJ mol–1
You are provided with the following.
FA 4, impure solid sodium carbonate
FA 5, 2.0 mol dm–3 hydrochloric acid
Measurement of temperature change
(a) Follow the instructions below to determine the percentage purity of the sodium
carbonate.
You will carry out the experiment twice.
• Weigh the empty weighing bottle.
• Reweigh the bottle with between 4.00 g and 4.50 g of FA 4.
• Support the plastic cup in the 250 cm3 beaker and add to it, from a measuring
cylinder, 50 cm3 of FA 5.
• Measure and record the steady temperature of the FA 5 in the plastic cup.
• Add the FA 4 from the weighing bottle to the plastic cup, a little at a time to
prevent acid spray. Stir and record the highest temperature reached.
• Reweigh the empty weighing bottle.
In an appropriate format in the space below, record
• all measurements of mass and temperature,
• the mass of FA 4 used, m,
• the temperature rise, ΔT.
Empty and rinse the plastic cup.
Repeat the experiment.
Results