Summary AQA A level Chemistry All Required Practicals
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Course
Required Practicals
Institution
AQA
Details all steps to every required practical, as well as why each step is taken. Includes (where applicable) Sources of error, safety precautions, results and analysis, calculations, equations and visual guides
1. Make up a volumetric solution and carry out a simple acid–base titration
2. Measurement of an enthalpy change
3. Investigation of how the rate of a reaction changes with temperature
4. Carry out simple test-tube reactions to identify:
I. Cations – Group 2, NH4+
II. Anions – Group 7 (halide ions), OH–, CO32–, SO42–
5. Distillation of a product from a reaction
6. Tests for alcohol, aldehyde, alkene and carboxylic acid
7. Measuring the rate of reaction:
I. By an initial rate method
II. By a continuous monitoring method
8. Measuring the EMF of an electrochemical cell
9. Investigate how pH changes when a weak acid reacts with a strong base and when a
strong acid reacts with a weak base
10. Preparation of:
I. A pure organic solid and test of its purity
II. A pure organic liquid
11.Carry out simple test-tube reactions to identify transition metal ions in aqueous solution
12.Separation of species by thin-layer chromatography
Extra notes (Steps have been summarised into what will be in papers, some methods have
been slightly altered to fit mark schemes better)
,1. Make up a volumetric solution and carry out a simple
acid–base titration
Making up a Volumetric Solution:
Method:
3 -3
1) Calculate the mass of solid needed to produce 250cm of a 0.1 mol dm solution.
2) Weigh the mass of an empty, clean weighing boat on a 2d.p. balance.
3) Add the calculated mass of solid into the weighing boat using a spatula and reweigh.
3
4) Pour the contents of the weighing boat into a 250cm beaker and reweigh.
The difference in mass is an accurate measurement of the mass of solid that is added
to the beaker.
3
5) Add approx. 100cm of distilled water to the beaker and stir using a glass rod
until all of the solid dissolves.
3
It does not matter if the volume of water added slightly exceeds 100cm , as the
3
volume must be made up to 250cm in the end.
Substances may not dissolve well in cold water, in which case the contents could be
heated gently.
3
6) Using a funnel, pour the contents of the beaker into a 250cm volumetric flask and
rinse the glass rod / beaker contents into the flask.
Rinsing the glassware ensures that all of the salt is transferred into the volumetric
flask.
7) Carefully add distilled water to the volumetric flask up to the graduated line.
Use a dropping pipette for the last few drops to ensure you don’t overshoot the
graduated mark. Fill until the bottom of the meniscus sits on the graduated line.
8) Stopper the flask.
A stopper will prevent water from evaporating from the flask. If water evaporates
from the flask, the concentration of the
solution will increase.
9) Invert the flask to mix the contents.
Only invert the flask after reaching the
graduated line, otherwise water will remain
, on the edges of the flask and gradually add to the solution, reducing the
concentration.
Inverting will ensure that the concentration of the substance is uniform throughout
the solution.
Potential Sources of Error
• If using an anhydrous salt, make sure it has not picked up water otherwise its mass
values will not be accurate.
• Balance only gives values to 0.01g.
• With dark liquids, it can be difficult to see the meniscus – place a piece of white
paper behind the marker clearer to see.
Reducing Uncertainty in Measuring Mass
• Use a balance with a higher resolution.
• Use a larger mass of solid.
• Weigh the sample before and after the addition of the solid to the beaker (weigh by
difference).
Acid-Base Titration
Method:
1. Rinse the burette with the acid and the pipette
with the alkali. Do not rinse with water to avoid
diluting the solutions.
3 3
2. Pipette 25cm of the alkali into a 250cm conical flask using a volumetric pipette.
A flask is used in preference to a beaker, as it is easier to swirl a mixture in a flask
without spilling its contents.
Touch the surface of the solution with the pipette to ensure the correct amount is
added.
A small amount of the solution will remain in the pipette and the pipette is
calibrated to include this volume.
3. Fill the burette with the acid and remember to remove the funnel from the top of the
burette. Removing the funnel ensures that no additional acid drips into the burette
during the titration, as this will decrease the size of the titre volume.
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