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
71–80 of 423 · Normal
Question 71
6 marks · Normal
Answer and see the solution →A research chemist is given three samples labelled A, B, and C. She wants to classify them and analyse their composition using paper chromatography.
(a)[3 marks]Sample A consists only of nitrogen gas. Sample B contains sodium chloride crystals. Sample C is a solution made by dissolving food dye in water. Classify each sample as an element, compound, or mixture.
(b)[1 mark]The chemist uses paper chromatography to separate the dyes in Sample C. After running the experiment, she observes three coloured spots at different distances from the pencil line. What does this result tell you about the composition of Sample C?
(c)[2 marks]Explain how you could use the chromatogram to identify if Sample C contains the same dyes as a reference mixture of known dyes.
Question 72
6 marks · Normal
Answer and see the solution →A scientist wants to investigate the substances present in two unknown samples using paper chromatography. She also wants to classify the samples as elements, compounds, or mixtures.
(a)[2 marks]Describe how the scientist can use the appearance of the chromatogram to decide if each sample is a pure substance or a mixture.
(b)[2 marks]The scientist measures the distances on the chromatogram for one spot as follows: Distance from pencil line to spot centre: 2.4 cm Distance from pencil line to solvent front: 4.0 cm Calculate the Rf value for this spot. Show your working.
(c)[2 marks]Give the definitions for (i) element, (ii) compound, and (iii) mixture.
Question 73
6 marks · Normal
Answer and see the solution →A student finds a white powder in the laboratory labelled 'Sample X'. She wants to check if it is a pure substance or a mixture, and then investigate its components using paper chromatography.
(a)[2 marks]Describe how the student could use melting point measurements to determine whether Sample X is pure or a mixture.
(b)The student performs a paper chromatography experiment with a spot of Sample X and three reference dyes A, B and C on the same chromatography paper. The chromatogram is developed using a suitable solvent.
The diagram below shows the results.
Chromatogram of Sample X and reference dyes after development The solvent front has moved 6.0 cm from the pencil line. The spots are found at the following distances above the pencil line: Sample X: 2.0 cm, 4.5 cm Dye A: 2.0 cm Dye B: 4.5 cm Dye C: 3.7 cm
(i)[1 mark]How many different dyes are present in Sample X? Explain your answer.
(ii)[1 mark]State which reference dyes are found in Sample X. Give your reasoning.
(c)[2 marks]Calculate the R_f value for the spot at 3.7 cm. Show your working.
Question 74
6 marks · Normal
Answer and see the solution →A teacher finds a powdery sample on a lab bench. She wants to find out if it is a pure substance or a mixture. She records the melting point, then runs paper chromatography on the dissolved sample, using water as the solvent. The chromatogram below shows her results.
Melting behaviour of sample X Sample X observations Melting starts at 87°C Melting finishes at 97°C Chromatogram obtained from sample X and three known dyes (Dye A, Dye B, Dye C) The solvent front travelled 8.0 cm from the pencil line.
(a)[2 marks]Explain what the melting point results show about whether sample X is a pure substance or a mixture.
(b)[2 marks]Describe how paper chromatography was carried out in this investigation. Include the key steps.
(c)[1 mark]Use the chromatogram to identify which dyes are present in sample X. State your reasoning.
(d)[1 mark]Calculate the R_f value for the dye in sample X that matches Dye B. Give your answer to two decimal places.
Question 75
3 marks · Normal
Answer and see the solution →A molecule of ammonia (NH₃) contains both nitrogen and hydrogen atoms.
(a)[3 marks]Calculate the total number of atoms in two molecules of ammonia (NH₃). Show your working.
Question 76
3 marks · Normal
Answer and see the solution →Explain why oxygen can exist as O₂ molecules, but helium does not form molecules under normal conditions. Use your knowledge of atoms and molecules.
Question 77
1 mark · Normal
Answer and check →Which statement best describes a molecule?
- A.A single atom of an element
- B.Two or more atoms chemically bonded together
- C.A mixture of different elements
- D.A group of unbonded atoms
Question 78
2 marks · Normal
Answer and see the solution →State two differences between an atom and a molecule.
Question 79
2 marks · Normal
Answer and see the solution →State what is meant by:
(a)[1 mark]an atom
(b)[1 mark]a molecule
Question 80
4 marks · Normal
Answer and see the solution →This question is about atoms and molecules.
(a)[1 mark]Copper (Cu) is an element. State what you would have if you kept cutting a piece of copper into smaller pieces until you could not cut it any further and still have copper.
(b)[1 mark]Describe what a molecule is.
(c)[1 mark]Give one example of a substance made of molecules that contain atoms of different elements.
(d)[1 mark]Explain why all molecules are made up of atoms, but not all atoms are part of molecules.