GCSE Combined Science Analysis & chromatography questions by topic

This question is about purity and formulations.

1. (a)State what a pure substance is in chemistry.[1]
2. (b)Give one property that can be measured to check a solid's purity.[1]
3. (c)State what is special about the amount of each ingredient in a formulation.[1]
4. (d)Name one example of a formulation.[1]

This question is about the gas tests.

1. (a)Name the gas that turns limewater cloudy.[1]
2. (b)Describe what is heard when hydrogen is tested with a lighted splint.[1]
3. (c)State what happens to a glowing splint placed in oxygen.[1]
4. (d)State the observation made with damp litmus paper in chlorine.[1]

This question is about setting up a chromatography experiment.

1. (a)Name the stationary phase in paper chromatography.[1]
2. (b)Name the mobile phase in paper chromatography.[1]
3. (c)Explain why the start line is drawn in pencil.[1]
4. (d)Explain why the start line must be above the solvent level.[1]

A data book lists a substance as melting at 80 °C. A sample of the substance melts gradually from 71 °C to 79 °C.

1. (a)State whether the sample is pure. Give a reason.[2]
2. (b)Describe how a pure sample of the substance would behave when heated to melting.[1]
3. (c)State what impurities do to the melting point of a solid.[1]

A student chromatographs a blue sweet dye. The spot moves 2.4 cm from the baseline; the solvent front moves 8.0 cm.

1. (a)Calculate the Rf value of the blue dye.[2]
2. (b)A reference table gives dye C an Rf of 0.30 in this solvent. State what the student can conclude.[1]
3. (c)Explain why the Rf value would be different if a different solvent were used.[2]

On one chromatogram, red dye R sits higher than blue dye B.

1. (a)State which dye has the larger Rf value.[1]
2. (b)Explain, in terms of the two phases, why R travels farther than B.[3]
3. (c)State one thing that must be identical for both dyes for the comparison to be fair.[1]

A sports drink lists water, sugar, salt, potassium salts, flavouring and colouring.

1. (a)State the name given to a mixture designed like this.[1]
2. (b)Explain why the amounts of sugar and salt are carefully measured.[2]
3. (c)Give two other product types that are made the same way.[2]

A black ink gives three separate spots on a chromatogram. The spot lowest on the paper is also the largest.

1. (a)State what the three spots show about the ink.[1]
2. (b)What does the largest spot suggest about the ink's composition?[1]
3. (c)Describe how the student finds the Rf of the lowest spot.[2]
4. (d)The lowest spot has Rf 0.25 and a known brown dye on the same paper also gives Rf 0.25. State a reasonable conclusion.[1]

A student carries out the required practical to identify the dyes in an unknown food colouring using four known reference dyes.

1. (a)Describe how the student should set up and run the experiment.[4]
2. (b)State one hazard and one precaution.[2]

An unknown food colouring is chromatographed. One spot moves 6.3 cm while the solvent front moves 9.0 cm. Reference dyes on the same paper: A = 0.25, B = 0.50, E = 0.70.

1. (a)Calculate the Rf of the unknown spot.[2]
2. (b)Identify the dye and justify the identification.[2]
3. (c)State what a single spot on the chromatogram suggests, and why it is not certain proof.[2]

Four colourless gas samples P, Q, R and S are tested. P relights a glowing splint. Q gives a squeaky pop with a lighted splint. R turns limewater cloudy. S bleaches damp litmus paper.

1. (a)Identify each of the four gases.[4]
2. (b)Name one hazard in testing sample S.[1]
3. (c)Explain why the litmus used for sample S must be damp.[1]

A lab receives two colourless liquids. One is claimed to be pure water, the other salt solution.

1. (a)Describe a melting- or boiling-point measurement that would tell them apart.[2]
2. (b)State the result expected for each liquid.[2]