A-Level Chemistry Practical Techniques & Calculations

Fill-in-the-blank flashcards covering key practical techniques, calculations, safety, and analytical methods required for A-level chemistry practical exams.

One potential error when using a gas syringe is that gas before the bung is inserted.

escapes

When drawing a gas syringe, always include markings on the barrel.

measurement

Moles of a gas at RTP can be calculated using the molar gas volume where 1 mol ≈ dm³.

24

When collecting gas over water, an up-turned cylinder is placed in a trough.

measuring

Irritant substances (dilute acids/alkalis) require wearing .

goggles

Corrosive chemicals (strong acids/alkalis) require goggles and should be kept away from .

skin

Flammable reagents must be kept away from flames.

naked

Toxic reagents should be handled with to avoid skin contact.

gloves

When measuring soluble gases like CO₂ with a gas syringe, some gas may dissolve, leading to an volume.

under-measured

In the CaCO₃–HCl gas-volume experiment, after each addition you quickly the bung to prevent gas loss.

re-seal

The lid on a crucible should be fitting to allow gaseous products to escape.

loose

Heating a wet crucible gives too large a mass loss because _ evaporates.

water

Small sample masses increase percentage in weighing measurements.

uncertainty

Graduated volumetric flasks have calibration mark(s) on the neck.

one

Always use a teat for the last few drops when making up to the mark.

pipette

A volumetric delivers one fixed volume with lower uncertainty than a measuring cylinder.

pipette

In titration, the phrase “titrate solution A with solution B” means A is in the flask.

conical

Phenolphthalein changes from pink in alkali to at the end-point.

colourless

Methyl orange is in alkali and red in acid; the end-point is orange.

yellow

Burette readings are recorded to two decimal places, ending in 0.00 or cm³.

0.05

Do not leave a in the burette during titration because drops may fall and alter the titre.

funnel

Only average titres (those within 0.10 cm³ of each other).

concordant

Replacing measuring cylinders with burettes lowers apparatus .

uncertainty

Increasing the titre volume (e.g., by using more dilute burette solution) percentage uncertainty.

decreases

For analogue equipment, the uncertainty of a single reading is ±0.5 of the scale division.

smallest

Water hydrolysis of halogenoalkanes is followed by adding nitrate to form AgX precipitates.

silver

The fastest precipitate in halogenoalkane hydrolysis is AgI because the bond is weakest.

C–I

Partial oxidation of a primary alcohol to an aldehyde requires immediate of the product.

distillation

Full oxidation of a primary alcohol to a carboxylic acid is carried out under .

reflux

Anti-bumping granules are added to prevent vigorous, boiling.

uneven

During distillation the thermometer bulb must sit at the where vapours enter the condenser.

T-junction

The layer with lower density in a separating funnel is usually the layer.

organic

A suitable drying agent such as anhydrous chloride must be insoluble and unreactive.

calcium

In steam distillation, the product distils at a temperature preventing decomposition.

lower

A positive Tollen’s test gives a silver on the tube wall.

mirror

Fehling’s solution gives a red precipitate of oxide with aldehydes.

Cu₂O

2,4-DNP forms an orange precipitate with both aldehydes and .

ketones

Carboxylic acids fizz with sodium carbonate releasing gas.

CO₂

In calorimetry, energy change Q is calculated using Q = m × c × ΔT, where c for water is J g⁻¹ K⁻¹.

4.18

To correct for heat loss in a calorimetry experiment, plot temperature vs time and back to mixing time.

extrapolate

The half-life of a first-order reaction is of concentration.

independent

In a clock reaction, the initial rate is proportional to 1/.

time

Plotting ln k against 1/T yields a straight line whose gradient equals –Eₐ divided by the constant.

gas (R)

A salt bridge contains a solution such as nitrate to maintain electrical neutrality.

potassium

In an electrochemical cell, electrons flow from the reactive metal to the less reactive metal.

more

Only dilute sulfuric acid is suitable for MnO₄⁻ titrations; HCl is unsuitable because Cl⁻ would be .

oxidised

EDTA complexes metal ions in a fixed ratio.

1 : 1

Mn²⁺ produced in the MnO₄⁻/C₂O₄²⁻ reaction acts as an catalyst.

auto

Recrystallisation requires dissolving the impure solid in the possible volume of hot solvent.

minimum

Impurities lower and the melting point range of a solid.

broaden

During aspirin synthesis, ethanoic anhydride is preferred over acetyl chloride because it is less .

corrosive

TLC Rf value is calculated as distance moved by substance divided by distance moved by .

solvent front

Choose a TLC developing solvent so that solvent level is the pencil baseline.

below

Spectrophotometry relies on the fact that light absorption is to concentration.

proportional

Adding ammonia to Cu²⁺ forms [Cu(NH₃)₄(H₂O)₂]²⁺ which gives a deep colour suitable for colorimetry.

blue

In the ester Kc experiment, sodium hydroxide titrates both residual acid and the catalyst.

sulfuric

For the ester equilibrium, Kc expression is [ester][water] / ([acid][]).

alcohol

Quenching a reaction sample can be achieved by adding excess sodium to neutralise acid.

hydrogencarbonate

A spectrometer’s colour filter is chosen to transmit the colour absorbed by the solution.

least

In uncertainty calculations, total percentage apparatus uncertainty is found by individual uncertainties.

adding

To reduce burette percentage uncertainty, aim for a titre volume.

larger

Vacuum (Büchner) filtration uses a water pump to create a and speed up separation.

vacuum

Autocatalysis is observed when a reaction product, such as Mn²⁺, the reaction rate.

increases

Steam distillation is advantageous for isolating high-boiling compounds because the mixture boils when the total pressure equals atmospheric.

vapour

During gas collection experiments, a gas syringe typically has a maximum capacity of cm³.

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