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Experimental Chemistry Starting Check · G3 Pure and O-Level Chemistry

Check what you know about G3 Pure Chemistry Experimental Chemistry and practise what needs work; apparatus skills still need supervised practical work.

SEC G3 Pure Chemistry 2027

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Answer 10 short questions. It shows what to work on next and doesn't count towards mastery.

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A mixture contains insoluble sand in sodium chloride solution. To recover the sand and salt separately, what should be done first?

Filter and keep the paper as the dissolved salt fraction.
Distil and collect the condensed water as the sand fraction.
Evaporate to dryness and keep the sand and salt together.
Filter and keep the sand residue and salt-solution filtrate separately.

Which mixture can be separated by heating so that one component sublimes while the other remains solid?

Two solids that both remain solid at the chosen temperature.
Two solids that both sublime together at the chosen temperature.
Two solids that both melt before either enters the gas phase.
A subliming solid mixed with a non-subliming solid under the chosen conditions.

Two miscible liquids have close boiling points and can be separated by distillation. Which setup improves their separation through repeated vaporisation and condensation?

Fractional distillation.
A separating funnel.
Filtration.
Simple distillation without a fractionating column.

Two immiscible liquids have settled into layers. Which apparatus separates the layers by controlled drainage?

Filter funnel and filter paper.
Evaporating basin.
Separating funnel.
Fractionating column.

Heat escapes from an open calorimetry cup. How does this usually affect the measured temperature rise for an exothermic reaction?

It has no effect because energy is conserved globally
It guarantees that the measured temperature falls below its initial value
It makes the rise too small
It makes the rise too large

Before starting titration, what should you do with the burette?

Rinse it with distilled water only
Rinse it with the solution (titrant) that will be in the burette
Dry it with a paper towel inside
Leave it half full from the last experiment

A student draws a best-fit line but uses only two data points and ignores the rest. What is the best criticism?

It is fine; two points always define a line
A best-fit line should reflect all points/trend, not just two points
They should always use a curve instead
They should plot in a table instead of a graph

In a fair test, which variable should you change deliberately?

Dependent variable
Control variable
Independent variable
Random variable

A mixture of colourless amino acids is spotted on a pencil baseline, and the chromatography paper is stood in solvent whose level is below the baseline. When the solvent front is 8.0 cm above the baseline, the paper is dried and sprayed with a locating agent. One spot then appears 2.0 cm above the baseline. Which statement is correct?

The locating agent makes the colourless spot visible, and the Rf value of that amino acid is 0.25.
The locating agent separates the amino acids, and the Rf value is 4.0.
The solvent level should have been above the baseline, and the Rf value is 0.25.
The locating agent is needed because amino acids do not dissolve, and the Rf value is 2.0.

Pure paracetamol melts sharply at 169 °C. A sample intended for making tablets melts gradually between 160 °C and 166 °C. Which conclusion is correct?

The sample is impure, and this matters because impurities in a drug could be harmful or change the effective dose.
The sample is pure, because its melting point is close to 169 °C.
The sample is impure, but purity does not matter for drugs as long as the tablet mass is correct.
The sample is a different pure substance that melts at 160–166 °C.

Practise

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About 10 minutes

Questions are picked at random each time you start. You'll see the answer after each question. It's for practice only and doesn't count towards mastery.

Recent attempts

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This check needs JavaScript to record answers. The reviewed questions are listed below for study.

Two immiscible liquids have settled into layers. Which apparatus separates the layers by controlled drainage?

Filter funnel and filter paper.
Evaporating basin.
Separating funnel.
Fractionating column.

Why is the purity of an active ingredient checked before it is used to make a medicine?

A purity result is enough to choose the dose without measuring the amount of ingredient.
A purity result shows that storage conditions cannot affect the medicine.
Impurities can affect the amount of active substance delivered or introduce harmful contaminants.
Impurities matter only when they change the colour of the ingredient.

One component of a solid mixture sublimes on heating while the other remains solid. How can the sublimed component be collected separately as a solid?

Let its vapour reach a cooler surface and deposit there.
Keep only the non-subliming residue in the heated container.
Pass its vapour through a warm surface that prevents deposition.
Allow its vapour to escape without collecting it.

A dissolved solid decomposes under strong heating. It is much more soluble in hot water than in cold water, and gentle warming is safe for it. Which sequence obtains dry crystals?

Boil rapidly to dryness, then scrape out the solid.
Filter the dilute solution, then dry the filter paper.
Distil the solution, then keep only the condensed water.
Concentrate gently, cool, filter off the crystals and dry them.

A paper chromatogram contains separated colourless substances. When should a suitable locating agent be applied to reveal them?

As a replacement for the solvent at the start.
Before the sample is placed on the start line.
After the solvent run has separated the substances.
While the solvent front is still moving past the spots.

Why is the sample spot on the start line placed above the initial solvent level in paper chromatography?

To stop the solvent from rising through the paper.
To prevent the sample dissolving directly into the solvent reservoir.
To make the paper retain the sample as an insoluble residue.
To stop the solvent reaching the sample during the run.

After filling the burette, why should you run some solution through the tap into a beaker?

To waste solution so the titration is harder
To remove air bubbles from the jet/tap so readings are accurate
To wash the indicator into the burette
To change the concentration

A sample is thought to be liquid X. At the same pressure as the reference measurement, it boils sharply at 78 °C, the reference boiling point of pure X. What does this evidence support?

The sample is impure because it boils sharply.
The sample contains a known mass of X.
The proposed identity and purity of the sample.
The sample is certainly X with no impurities.

A student writes: “Keep the temperature constant.” Why is this incomplete?

It does not state the fixed temperature value
It does not state how temperature will be kept constant
It measures temperature but does not control it
It proposes taking a mean instead of controlling temperature

On a paper chromatogram, a spot centre is 3.0 cm from the start line and the solvent front is 5.0 cm from that line. What is the Rf value?

0.60
1.7
2.0
8.0

A chromatogram of black ink shows three separated spots. Which explanation links the observation to classification?

The ink contains at least three soluble components and is therefore a mixture
Each spot is an atom, so the ink is one element
Three spots prove the ink has one fixed chemical formula
Chromatography chemically decomposed one pure compound

Why should you choose two points far apart when calculating the gradient of a best-fit line?

It makes the gradient always larger
It reduces percentage uncertainty in the gradient calculation
It forces the line through the origin
It makes the graph look smoother

A temperature probe range is 0–50 °C, but the reaction may reach 80 °C. What should be done?

Select a probe or range that includes the expected maximum
Use the same probe and treat every reading above 50 °C as exact
Lower the sampling frequency but retain the 0–50 °C probe.
Extrapolate every displayed 50 °C reading to 80 °C

Practise after feedback

After a check, practise the skills it showed you need to work on.

About 10 minutes

Questions are picked at random each time you start. You'll see the answer after each question. It's for practice only and doesn't count towards mastery.

Recent attempts

History is stored only in this browser.

No completed attempts are saved yet.

This check needs JavaScript to record answers. The reviewed questions are listed below for study.

Two miscible liquids have close boiling points and can be separated by distillation. Which setup improves their separation through repeated vaporisation and condensation?

Fractional distillation.
A separating funnel.
Filtration.
Simple distillation without a fractionating column.

A food ingredient may contain an unwanted contaminant. Why is its purity checked before use?

To establish safety from appearance alone.
To prove safety from one unreferenced boiling-temperature reading.
To confirm that any contaminant present is harmless without identifying it.
To detect contamination that could affect composition, quality or safety.

Which apparatus is used to separate immiscible liquids such as oil and water?

Burette; Acid-Base titration
Pipette; Measuring fixed volumes
Separating Funnel; Immiscible liquids
Fractionating Column; Miscible liquids

Which method is most suitable for separating iron filings from sulfur powder?

Magnetic separation (using a magnet)
Filtration
Crystallisation
Fractional distillation

Why does ordinary filtration fail to recover dissolved sodium chloride as a solid from its aqueous solution?

The sodium chloride evaporates before the water reaches the paper.
Dissolved ions pass through the filter paper with the water.
The sodium chloride ions are retained as a dry residue.
The sodium chloride has changed chemically into water.

A mixture contains sand, salt and water. Which method recovers dry sand and pure water, leaving salt as a separate residue?

Filter and dry the sand, then distil the filtrate and collect the condensed water
Filter to collect salt, then evaporate sand through the paper
Use only a magnet because all three components are magnetic
Use a separating funnel because salt solution and sand form two liquid layers

Why is a suitable locating agent applied after paper chromatography of colourless substances?

To mark how far the solvent front travelled.
To make the separated colourless spots visible.
To move the separated spots farther up the paper.
To remove the solvent from the paper.

An unknown dye and a known dye produce spots at the same height. Which setup makes this height comparison meaningful?

Different start lines on the same sheet, without measuring their positions.
Different solvents and papers, each run for a different distance.
The same sheet and solvent run, with both samples on the same start line.
Different chromatograms compared only because their spots have the same colour.

If solution splashes onto the side of the conical flask above the liquid level, what should you do?

Ignore it; it makes no difference
Rinse the sides down with distilled water from a wash bottle
Add more indicator until it changes back
Pour the mixture into a measuring cylinder

A sample is labelled solid X. Pure X has a reference melting point of 80 °C. Which measured melting behaviour best supports the sample being pure X?

A sharp melting point near 80 °C.
A broad melting range from 68 °C to 78 °C.
A sharp melting point near 60 °C.
A broad melting range from 50 °C to 90 °C.

A dye sample produces three spots on a chromatogram. What is the correct conclusion?

The sample is pure
The sample is a mixture of three substances
The sample is a mixture of two substances
The result is meaningless because chromatography cannot separate dyes

Which is the best dependent variable for comparing reaction rate using a gas syringe?

Time taken to collect one final, unspecified volume
Volume of gas collected vs time
Total gas volume after the reaction has stopped
Change in reactant mass without recording time

Which is the best way to read a value from a graph at x = 12 s?

Guess the y-value without drawing anything
Draw a vertical line up from 12 s to the best-fit line, then across to the y-axis
Use only the nearest plotted point even if it is far away
Read the value from the table title

A reaction reaches its maximum temperature within 20 s. Which sampling interval is most suitable?

One reading every 30 seconds.
One reading each second
One reading only at 20 seconds.
One reading before mixing only

Experimental Chemistry Starting Check · G3 Pure and O-Level Chemistry

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