Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Unit
Principles of Chemistry
991 practice questions
Topics covered
- States of Matter102 practice questions
- Elements, Compounds and Mixtures69 practice questions
- Atomic Structure108 practice questions
- The Periodic Table103 practice questions
- Chemical Formulae, Equations and Calculations Part 119 practice questions
- Chemical Formulae, Equations and Calculations Part 2144 practice questions
- Ionic Bonding143 practice questions
- Covalent Bonding68 practice questions
- Metallic Bonding19 practice questions
- Electrolysis198 practice questions
Practice questions
21–30 of 161 · Hard
Question 21
5 marks · Hard
Answer and see the solution →A chemist needs to separate and collect pure ethanol from a mixture of ethanol and water. Both substances are completely miscible. The boiling point of ethanol is 78°C and that of water is 100°C.
(a)[1 mark]Name the separation technique that should be used to obtain pure ethanol from the mixture.
(b)[2 marks]Describe how this technique separates ethanol from water. Include reference to their boiling points and any specific apparatus that must be used.
(c)[1 mark]State one reason why ethanol collected from this process is not completely pure.
(d)[1 mark]Draw a labelled diagram of the key apparatus used for this separation.
Question 22
2 marks · Hard
Answer and see the solution →A student is given a mixture containing sand, sodium chloride, and water. For each of the following, state the most suitable separation technique and explain your choice briefly.
(a)[1 mark]To obtain dry sand from the mixture.
(b)[1 mark]To obtain pure sodium chloride crystals from the mixture.
Question 23
2 marks · Hard
Answer and see the solution →A blue dye in a chromatography experiment travels 1.5 cm from the pencil line. The solvent front moves 5.0 cm from the pencil line. Calculate the R_f value for the blue dye. Show your working.
Question 24
5 marks · Hard
Answer and see the solution →A student wants to find out whether the green colour in a piece of candy is due to a single dye or a mixture of dyes. Describe how you would carry out a paper chromatography experiment to investigate this. Include details about:
(a)[1 mark]the preparation of the chromatography paper and application of the sample
(b)[1 mark]how to set up and run the chromatography
(c)[1 mark]how to mark the solvent front and why this is important
(d)[1 mark]what you would expect to observe if the green dye is a mixture of dyes
(e)[1 mark]one step you should take to make sure your results are reliable
Question 25
2 marks · Hard
Answer and see the solution →Explain why the R_f value must always be between 0 and 1 in a paper chromatography experiment.
Question 26
7 marks · Hard
Answer and see the solution →A chemist receives a coloured powder described as a mixture of food dyes and metal salts. She wants to find out if the powder is a mixture or a compound, and which dyes are present.
(a)[2 marks]State two differences between a mixture and a compound, using the chemist’s powder as an example.
(b)The chemist dissolves a small amount of the powder in water and runs a paper chromatography experiment alongside three known food dyes (dye A, dye B and dye C). The chromatogram below was produced:
Chromatogram from the experiment Spot distances from pencil line (cm) Sample Distance travelled by dye spot (cm) Powder 2.0 Dye A 2.0 Dye B 4.3 Dye C 6.0 (i)[2 marks]Calculate the R_f value for the dye in the powder. Show your working.
(ii)[1 mark]Suggest which dye(s) are present in the powder, using the chromatogram results.
(iii)[2 marks]Explain why it is important to measure from the pencil line to the centre of each spot when calculating the R_f value.
Question 27
7 marks · Hard
Answer and see the solution →A chemist is given two samples labelled X and Y. She suspects that X is a compound and Y is a mixture. She performs paper chromatography on both samples along with three dyes labelled D1, D2, and D3 on the same sheet.
Chromatogram for samples and dyes Distances moved by spots (all from the pencil line at the bottom of the paper) Substance Distance moved by spot (cm) Solvent front 5.0 X 2.0 Y (spot 1) 1.0 Y (spot 2) 3.0 D1 1.0 D2 2.0 D3 3.0 (a)[3 marks]Classify samples X and Y as elements, compounds, or mixtures, using the results of the chromatogram. Explain your reasoning.
(b)[2 marks]For each spot found for Y, identify which dye(s), if any, are present in Y.
(c)[2 marks]Calculate the R_f value for the spot found for X.
Question 28
2 marks · Hard
Answer and see the solution →State the meaning of the following terms:
(a)[1 mark]atom
(b)[1 mark]molecule
Question 29
5 marks · Hard
Answer and see the solution →Ammonia has the chemical formula NH₃.
(a)[1 mark]State what an atom is.
(b)[1 mark]Describe what is meant by a molecule.
(c)[1 mark]How many atoms are present in one molecule of ammonia?
(d)[1 mark]Write the names of the elements that form a molecule of ammonia.
(e)[1 mark]Explain, using ammonia as an example, how a molecule is different from an atom.
Question 30
2 marks · Hard
Answer and see the solution →Give one similarity and one difference between atoms and molecules.
(a)[1 mark]State one way in which atoms and molecules are similar.
(b)[1 mark]State one way in which atoms and molecules are different.