AQA GCSE Combined science Chemistry required practicals

paper 1

how do you conduct the making salts practical

• Add excess insoluble metal oxide (e.g. copper(II) oxide) to warm sulfuric acid.

• Filter to remove excess.

• Heat filtrate to crystallise the salt.

what is the independent variable of the making salts practical

Type or amount of metal oxide

what is the dependant variable of the making salts practical

Mass of salt produced

what is the control variable of the making salts practical

Volume/concentration of acid, temperature

what are the limitations of the making salts practical

• Heating may cause spitting

• Loss of product during filtration

what are the common errors of the making salts practical

• Not all metal oxide reacts — must use excess

• Salt left wet — not fully crystallised

how do you conduct the neutralisation practical

• Use pipette to add alkali to a conical flask.

• Add indicator (e.g. phenolphthalein).

• Slowly add acid from burette until indicator changes colour.

• Repeat for accuracy and calculate mean.

what is the independent variable of the neutralisation practical

Volume of acid added

what is the dependant variable of the neutralisation practical

colour change / volume of acid for neutralisation

what is the control variable of the neutralisation practical

Concentration of alkali, indicator type

what are the limitations of the neutralisation practical

Human error in reading burette

what are the common errors of the neutralisation practical

• Not swirling the flask

• Overshooting the end point

how do you conduct the electrolysis practical

• Set up circuit with electrodes in an electrolyte solution.

• Run electrolysis and observe products at electrodes (e.g. hydrogen, chlorine).

what is the independent variable of the electrolysis practcal

Type of electrolyte

what is the dependant variable of the electrolysis practical

Products formed at electrodes

what are the control variables of the electrolysis practical

Volume of solution, time

what are the limitations of the electrolysis practical

Gases may escape before collection

what are the common errors of the electrolysis practical

Not recognising gas correctly (e.g. chlorine test with damp litmus)

how do you conduct the temperature change required practical

• Mix measured volumes of reactants (e.g. acid + alkali) in polystyrene cup.

• Record temperature at start and peak temperature reached.

what is the independent variable of the temperature change practical

Type or concentration of reactants

what is the dependant variable of the temperature change practical

Temperature change

what is the control variable of the temperature change practical

Volume of reactants, cup used

what are the limitations of the temperature change practical

Heat loss to surroundings

what are the common errors of the temperature change practical

• Inaccurate temperature readings

• Stirring inconsistently