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GCSE Chemistry Practice Questions

Practice exam-style questions covering all GCSE Chemistry topics. Each question includes detailed step-by-step solutions.

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Question 1
Atomic Structure Easy

An atom has 11 protons, 12 neutrons and 11 electrons.

What is the mass number of this atom?

Solution:
  1. Mass number = number of protons + number of neutrons
  2. Given: protons = 11, neutrons = 12
  3. Calculate: Mass number = 11 + 12 = 23
Answer: 23
Question 2
Chemical Reactions Medium

Balance the equation:

Na + Cl₂ → NaCl

Solution:
  1. Count atoms on each side:
    Left: 1 Na, 2 Cl
    Right: 1 Na, 1 Cl
  2. Chlorine is unbalanced - need 2 NaCl on right
  3. This requires 2 Na on left
  4. Balanced equation: 2Na + Cl₂ → 2NaCl
Answer: 2Na + Cl₂ → 2NaCl
Question 3
Bonding Easy

What type of bonding is present in sodium chloride (NaCl)?

Solution:
  1. Sodium is a metal (Group 1)
  2. Chlorine is a non-metal (Group 7)
  3. Metals and non-metals form ionic bonds
  4. Sodium loses 1 electron to become Na⁺
  5. Chlorine gains 1 electron to become Cl⁻
  6. Electrostatic attraction between ions forms ionic bond
Answer: Ionic bonding
Question 4
Quantitative Chemistry Medium

Calculate the relative formula mass (Mr) of calcium carbonate (CaCO₃).

Ar: Ca = 40, C = 12, O = 16

Solution:
  1. CaCO₃ contains: 1 Ca, 1 C, 3 O
  2. Add up relative atomic masses:
  3. Mr = (1 × 40) + (1 × 12) + (3 × 16)
  4. Mr = 40 + 12 + 48
  5. Mr = 100
Answer: 100
Question 5
Moles Hard

Calculate the number of moles in 10g of calcium carbonate (CaCO₃).

Mr of CaCO₃ = 100

Solution:
  1. Use the formula: moles = mass / Mr
  2. Given: mass = 10 g, Mr = 100
  3. Calculate: moles = 10 / 100 = 0.1 mol
Answer: 0.1 mol
Question 6
Organic Chemistry Medium

What is the general formula for alkanes?

Solution:
  1. Alkanes are saturated hydrocarbons
  2. They contain only single C-C bonds
  3. Each carbon is bonded to maximum number of hydrogens
  4. Examples: CH₄ (n=1), C₂H₆ (n=2), C₃H₈ (n=3)
  5. General pattern: for n carbons, there are 2n+2 hydrogens
Answer: CₙH₂ₙ₊₂
Question 7
Acids & Bases Medium

Write the word equation for the reaction between hydrochloric acid and sodium hydroxide.

Solution:
  1. This is a neutralization reaction
  2. Acid + Base → Salt + Water
  3. Hydrochloric acid + Sodium hydroxide
  4. Forms sodium chloride (salt) and water
Answer: Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water
Question 8
Electronic Structure Hard

Write the electronic configuration of a chlorine atom (atomic number 17).

Solution:
  1. Atomic number = 17, so 17 electrons total
  2. Electron shells hold maximum: 1st = 2, 2nd = 8, 3rd = 8
  3. Fill shells in order:
    1st shell: 2 electrons
    2nd shell: 8 electrons
    3rd shell: 7 electrons (17 - 2 - 8 = 7)
Answer: 2, 8, 7
Question 9
Bonding Medium

Explain why diamond has a very high melting point.

Solution:
  1. Diamond is a giant covalent structure
  2. Each carbon atom is bonded to 4 other carbon atoms
  3. Strong covalent bonds throughout the structure
  4. Large amount of energy required to break these bonds
  5. Therefore, diamond has a very high melting point
Answer: Giant covalent structure with strong covalent bonds throughout, requiring large energy to break
Question 10
Electrolysis Hard

During the electrolysis of molten lead bromide, what is formed at the cathode?

Solution:
  1. Lead bromide contains Pb²⁺ and Br⁻ ions
  2. Cathode is the negative electrode
  3. Positive ions (cations) are attracted to cathode
  4. Pb²⁺ ions move to cathode
  5. At cathode: Pb²⁺ + 2e⁻ → Pb
  6. Lead metal is formed
Answer: Lead (Pb)