Experimental Chemistry Starting Check · G3 Combined Science Chemistry

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

SEC G3 Combined Science Chemistry component 2027

This check shows what to work on next. It and the practice after it don’t count towards mastery; only a later progress check can count towards your course progress.

Check what I know

Start here to see which parts you already know.

About 8 minutes

Answer 7 short questions. It shows what to work on next and doesn't count towards mastery.

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Before choosing evaporation, crystallisation or distillation for a solution, which information is needed?

The required product, its heat stability and how its solubility changes with temperature.
The required product and the colour of the heating apparatus.
The solvent volume and the pore size of filter paper, without identifying the product.
The highest temperature available, without considering the solute.

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.

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

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

Dependent variable
Control variable
Independent variable
Random variable

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 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

Why can an insoluble gas be collected over water?

It displaces water without a large fraction dissolving
Its low solubility means that it must be less dense than air.
The water chemically binds the gas and later releases it into the jar.
The gas must cool until it condenses inside the jar.

Practise

Work through questions with marking and feedback as you learn.

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 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.

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.

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 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

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.

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

Why are several values of the independent variable better than only a low and high value?

They reveal the pattern and make anomalies easier to recognise
They guarantee that every reading is accurate
They remove the need to control other variables
They replace the need to repeat measurements at each setting.

One sample produces two separate spots on a paper chromatogram. Assume neither the paper nor the solvent reacts with the sample. What does this show?

The sample is one pure substance because both spots moved.
The sample contains exactly two substances, with no others possible.
The paper has changed one substance into two new substances.
The sample contains at least two substances separated under these conditions.

How should a measured boiling temperature be used to assess a proposed liquid identity and purity?

Treat any single temperature reading as proof of identity.
Assume every impurity raises the boiling temperature by the same amount.
Treat a wide boiling range as confirmation of purity.
Compare with reference data at the same pressure and note whether boiling is sharp or over a range.

A temperature rise of about 7 °C is expected. Which thermometer feature is most useful?

A suitable range with small scale divisions around the expected temperatures
The widest possible range even if divisions are 10 °C apart
A scale that does not include the starting temperature
A scale marked every 1 °C but a response time longer than the experiment.

Why is a burette rinsed with the titrant before it is filled?

To neutralise the solution in the conical flask
To leave distilled water that makes the titrant easier to see
To avoid residual water diluting the titrant
To make the burette scale start at zero

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.

Before choosing evaporation, crystallisation or distillation for a solution, which information is needed?

The required product, its heat stability and how its solubility changes with temperature.
The required product and the colour of the heating apparatus.
The solvent volume and the pore size of filter paper, without identifying the product.
The highest temperature available, without considering the solute.

On a developed chromatogram, one component remains on the start line while another moves up the paper. What does this show?

The unmoved component has the greatest attraction to the mobile phase
The components migrate differently because their interactions with the paper and solvent differ.
Both components must be the same substance
The solvent moved downward from the top of the paper

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

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

A sample of a known solid melts over a range below the sharp reference melting point of the pure solid. What does this usually suggest?

It has a different mass from the reference sample, which changes the melting point.
It is purer than the reference material.
It contains impurities.
It has become a different pure substance with a sharp melting point.

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

Which setup is best for recording carbon dioxide volume against time?

A sealed flask connected only to a thermometer
A sealed reaction flask connected to a gas syringe
An open flask with a delivery tube missing
A filter funnel above the flask

Experimental Chemistry Starting Check · G3 Combined Science Chemistry

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