GCSE Chemistry Analysis questions by topic

This question is about pure substances and mixtures.

1. (a)State what is meant by a pure substance in chemistry.[1]
2. (b)Name one formulation and state what it is used for.[2]

A student runs a paper chromatogram of a food colouring.

1. (a)Name the mobile phase.[1]
2. (b)Explain why the dyes separate as the solvent rises.[1]
3. (c)State what a single spot tells you about the colouring.[1]

A spot moves 3.6 cm from the baseline while the solvent front moves 4.8 cm.

1. (a)State the equation for the Rf value.[1]
2. (b)Calculate the Rf value.[2]
3. (c)State the highest value an Rf can take.[1]

Identify each gas from its test result.

1. (a)Identify the gas in row 1.[1]
2. (b)Identify the gas in row 2.[1]
3. (c)Identify the gas in row 3.[1]
4. (d)Identify the gas in row 4.[1]

Complete the sentences about purity, formulations and melting points.

1. (a)A chemically pure substance contains only one … .[1]
2. (b)An impure solid melts over a … of temperatures, and its melting point is … than the pure value.[1]
3. (c)A formulation is a mixture designed as a useful … .[1]
4. (d)Give one example of a formulation.[1]
5. (e)State one practical way (other than melting point) to show a colourless liquid is pure water.[1]

A student runs a paper chromatogram. The solvent front travels 6.0 cm from the pencil baseline and a dye spot travels 5.4 cm.

1. (a)Calculate the Rf value of this dye spot.[2]
2. (b)State why the baseline is drawn in pencil rather than ink.[1]
3. (c)Name the stationary phase and the mobile phase in this experiment.[2]

(Chemistry only) A technician performs flame tests on five metal compounds.

1. (a)State the flame colour of lithium ions.[1]
2. (b)State the flame colour of sodium ions.[1]
3. (c)State the flame colour of potassium ions.[1]
4. (d)State the flame colour of calcium ions.[1]
5. (e)State the flame colour of copper ions.[1]

(Chemistry only) Sodium hydroxide solution is added to four unknown solutions.

1. (a)Identify the metal ion in solution A.[1]
2. (b)Identify the metal ion in solution B.[1]
3. (c)Identify the metal ion in solution C.[1]
4. (d)Identify the metal ion in solution D and explain how you know.[2]

Two dyes are chromatographed on the same paper. Dye P has an Rf of 0.72; dye Q has an Rf of 0.31.

1. (a)State which phase the paper is and which phase the solvent is.[2]
2. (b)State which dye travels further and how you know.[2]
3. (c)Explain, in terms of attraction, why the two dyes end up at different heights.[2]

A pharmaceutical factory checks the purity of a drug solid.

1. (a)Describe the melting behaviour expected of the pure drug.[2]
2. (b)State one reason purity matters for medicines.[2]

Four colourless gases are collected in test tubes and tested. The results: gas P gives a squeaky pop with a lighted splint; gas Q relights a glowing splint; gas R turns limewater cloudy; gas S bleaches damp litmus paper.

1. (a)Identify each gas P, Q, R and S.[4]
2. (b)Explain why the litmus paper must be damp for the test on gas S.[2]

Three separate unknown solutions are tested with the following results. Solution X: after adding dilute nitric acid and silver nitrate, a cream precipitate forms. Solution Y: after adding dilute nitric acid followed by barium nitrate solution, a dense white precipitate forms. Solution Z: adding dilute hydrochloric acid produces fizzing, and the gas turns limewater cloudy.

1. (a)Identify the negative ion in solution X, and explain why nitric acid is added first.[2]
2. (b)Identify the negative ion in solution Y.[1]
3. (c)Identify the negative ion in solution Z.[1]
4. (d)Write the ionic equation for the precipitate in solution Y.[2]

(Chemistry only) An unknown colourless solution is tested: dilute HCl makes it fizz, and the gas turns limewater cloudy; fresh samples then give a white precipitate with HCl + barium chloride, and no change with nitric acid + silver nitrate.

1. (a)Identify the ion causing the fizz and write the equation for the limewater change.[3]
2. (b)Identify the ion confirmed by the barium chloride test.[1]
3. (c)State what the silver nitrate result shows.[1]
4. (d)Write the ionic equation for the barium sulfate formation.[2]

(Chemistry only) A lab is choosing between manual flame tests and flame emission spectroscopy for monitoring metal ions in river water.

1. (a)Describe how FES identifies and quantifies a metal ion.[2]
2. (b)State two advantages of FES over manual flame tests.[2]
3. (c)State one disadvantage of FES.[1]
4. (d)Name the graph used to convert instrument readings into concentrations.[1]

A sweet manufacturer must prove its colouring contains exactly three dyes and measure each Rf.

1. (a)Describe how to set up the chromatogram, including two practical precautions.[4]
2. (b)Describe how the results show there are three dyes.[2]
3. (c)Describe how each Rf is calculated and used.[2]

(Chemistry only) A student tests a solution of a single fertiliser salt: NaOH gives a colourless solution (no precipitate); warming with NaOH releases a gas that turns damp red litmus blue.

1. (a)Identify the cation, explaining your reasoning.[2]
2. (b)Name the gas released and the ion it proves.[2]
3. (c)Name the salt.[2]

A suspect food colouring is chromatographed. The solvent front moves 6.5 cm. Three spots form, whose centres travel 2.0 cm, 4.4 cm and 5.2 cm from the baseline.

1. (a)Calculate the Rf value of each spot.[3]
2. (b)State what the number of spots shows about the colouring.[1]
3. (c)A banned dye has a published Rf of 0.68 in this solvent. Comment on whether the colouring contains it, and explain the limitation of matching by Rf alone.[3]

A water company must monitor drinking water for traces of lithium, barium and copper ions and decide between manual chemical tests and flame emission spectroscopy.

1. (a)Describe how flame emission spectroscopy identifies and measures a metal ion.[3]
2. (b)Give two advantages of spectroscopy over manual chemical tests for this job.[2]
3. (c)Give one limitation of spectroscopy.[1]
4. (d)Explain how reference spectra are used to interpret a sample’s results.[2]