GCSE Chemistry 3 — Questions and Answers
Question 1: Which of the following substances is a mixture rather than a pure compound?
- Water (H2O)
- Salt (NaCl)
- Air (Correct answer)
- Carbon dioxide (CO2)
Correct answer: Air
Air is a mixture of nitrogen, oxygen, argon, and other gases that are not chemically combined.
Question 2: In the periodic table, elements in the same group have the same number of:
- Protons
- Neutrons
- Electrons in the outer shell (Correct answer)
- Total electron shells
Correct answer: Electrons in the outer shell
Elements in the same group share the same number of outer shell (valence) electrons, giving them similar chemical properties.
Question 3: What type of reaction occurs when iron rusts in the presence of water and oxygen?
- Reduction
- Neutralisation
- Oxidation (Correct answer)
- Decomposition
Correct answer: Oxidation
Rusting is an oxidation reaction in which iron loses electrons and combines with oxygen to form iron(III) oxide.
Question 4: Which separation technique would best separate a mixture of salt and sand?
- Distillation
- Chromatography
- Dissolving in water, filtering, then evaporating (Correct answer)
- Fractional distillation
Correct answer: Dissolving in water, filtering, then evaporating
Salt dissolves in water while sand does not; filtering removes the sand, and evaporation recovers the salt.
Question 5: What is the pH of a neutral solution at 25°C?
- 0
- 7 (Correct answer)
- 14
- 1
Correct answer: 7
A neutral solution has equal concentrations of H⁺ and OH⁻ ions, giving a pH of exactly 7 at 25°C.
Question 6: Which of the following correctly describes an isotope?
- Atoms of different elements with the same mass number
- Atoms of the same element with different numbers of neutrons (Correct answer)
- Atoms of the same element with different numbers of protons
- Atoms with the same number of electrons but different charges
Correct answer: Atoms of the same element with different numbers of neutrons
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.
Question 7: When magnesium burns in oxygen, the product formed is:
- Magnesium chloride
- Magnesium hydroxide
- Magnesium oxide (Correct answer)
- Magnesium sulfate
Correct answer: Magnesium oxide
Magnesium reacts vigorously with oxygen to form magnesium oxide (MgO), a white solid.
GCSE Chemistry 3
Which of the following substances is a mixture rather than a pure compound?