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PearsonREVISION GUIDE
Edexcel
IAS
Chemistry
WCH13
,This guide includes details about the core practicals for A-level chemistry. It also contains information about other
experiments that often occur in A-level examinations. You may be asked to describe these experiments in details or
be asked about reasons for doing individual steps.
You may be asked about other unfamiliar experiments but these will be using the skills and techniques that
are described in the following experiments.
Safety and hazards
Irritant - dilute acid and alkalis- wear googles Hazardous substances in low
Corrosive- stronger acids and alkalis wear goggles concentrations or amounts
Flammable – keep away from naked flames will not pose the same risks as
Toxic – wear gloves- avoid skin contact- wash hands after use the pure substance.
Oxidising- Keep away from flammable / easily oxidised materials
Measuring gas volumes
Using a gas syringe Make sure you don’t leave gaps in
your diagram where gas could
Gas syringes can be used for a variety of escape
experiments where the volume of a gas
is measured, possibly to work out moles
of gas or to follow reaction rates.
Potential errors in using a gas
syringe •gas escapes before bung If drawing a gas syringe make
inserted •syringe sticks sure you draw it with some
some gases like carbon dioxide or sulphur dioxide measurement markings on the
are soluble in water so the true amount of gas is not barrel to show measurements can
measured. be made.
Alternatively gas volumes can be measured
The volume of a gas depends on pressure
and temperature so when recording ‘over water’ with an up-turned measuring
volume it is important to note down the cylinder in a trough of water
temperature and pressure of the room.
Moles of gas can be calculated from gas
volume (and temperature and pressure)
using ideal gas equation PV = nRT or using
the molar gas volume (1mol gas =24dm3
at room temperature and pressure
,Core Practical 1:Measure the molar volume of a gas
Detailed method
1. Measure 30 cm3 of 1 mol dm⁻3 ethanoic acid and transfer to a
conical flask.
2. Attach conical flask to gas syringe or use collection
over water method (see previous page)
3. Measure the mass of a weighing bottle with
Volume of CO2 in cm3
approximately 0.05 g of calcium carbonate
4. Add the calcium carbonate to the conical flask-
quickly resealing the bung so no gas escapes
5. Measure the final total volume of gas
6. Reweigh the empty weighing bottle test tube from step 3
7. Repeat the experiment several more times, increasing the mass of
calcium carbonate by about 0.05 g each time.
Mass of CaCO3 in g
Analysis
From the graph read the volume of CO2 given off with 0.25 g CaCO3
Work out the moles of CaCO3 in 0.25g = 0.25/100.1 = 2.5 x 10-
3 Assume the moles of CO2 = moles of CaCO3
Work out molar volume of CO2 = volume of CO2/ moles of CO2
Method for using a gas syringe to calculate the Mr of propanone
Extract 0.20 cm3 of propanone into a hypodermic syringe and then measure the mass of this syringe
using hand protection, remove a gas syringe from the oven and note the volume of air already in
the barrel – about 5 cm3.
inject the propanone through the self-seal cap into the barrel. The plunger will move straight away.
Put the gas syringe back into the oven.
Measure the mass of the empty hypodermic syringe immediately.
After a few minutes measure the volume of the gas in the gas syringe, record the temperature of the
oven shelf and the pressure of the room.
Example 1 : 0.150g of a volatile liquid was injected into a sealed gas syringe. The gas syringe was placed in an oven at
70oC at a pressure of 100kPa and a volume of 80cm3 was measured. Calculate the Mr of the volatile liquid (R = 8.31)
moles = PV/RT 100 kPa = 100 000 Pa
= 100 000 x 0.00008 / (8.31 x 343) 80 cm3 = 0.00008 m3
= 0.00281 mol
Mr = mass/moles
= 0..00281
= 53.4 g mol-1
, Heating in a crucible This method could be used for measuring mass loss in various
thermal decomposition reactions and also for mass gain
when reacting magnesium in oxygen.
The lid improves the accuracy of the
The water of crystallisation in calcium sulfate crystals can be experiment as it prevents loss of
removed as water vapour by heating as shown in the following solid from the crucible but should be
equation. CaSO4.xH2O(s) → CaSO4(s) + xH2O(g) loose fitting to allow gas to escape.
Method.
•Weigh an empty clean dry crucible and lid .
• Add 2g of hydrated calcium sulfate to the crucible and weigh
again •Heat strongly with a Bunsen for a couple of minutes •Allow
to cool
• Weigh the crucible and contents again
• Heat crucible again and reweigh until you reach a constant mass (
do this to ensure reaction is complete).
Large amounts of hydrated calcium sulfate, such as 50g,
should not be used in this experiment as the decomposition
is likely to be incomplete. Small amounts of the solid , such as
0.100 g, should not be used in this
The crucible needs to be dry otherwise a wet crucible experiment as the percentage
would give an inaccurate result. It would cause mass loss to uncertainties in weighing will be
be too large as the water would be lost when heating. too high.
Example 2. 3.51 g of hydrated zinc sulfate were heated and 1.97 g of anhydrous zinc sulfate were
obtained. Use these data to calculate the value of the integer x in ZnSO4.xH2O
Calculate the mass of H2O = 3.51 – 1.97 = 1.54g
Calculate moles of = 1.97 Calculate moles of = 1.54
ZnSO4 161.5 H2O 18
= 0.0122 =0.085
Calculate ratio of mole of = 0.0122 = 0.085
ZnSO4 to H2O 0.0122 0.0122
=1 =7
X=7
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