IGCSE Chemistry Practice Test 13

Correct: (B)

On melting, the particles gain energy and the lattice structure breaks down, so the particles can move around each other while staying close together.

Correct: (C)

Sublimation is the direct change from a solid to a gas, as seen with dry ice and iodine.

Correct: (A)

The random motion (Brownian motion) is caused by collisions with invisible air molecules moving randomly at high speed.

Correct: (D)

11 protons means the element is sodium, and the mass number is protons + neutrons = 11 + 12 = 23. It has equal protons and electrons, so it is a neutral atom.

Correct: (A)

Isotopes have the same atomic number (protons) but different mass numbers because they contain different numbers of neutrons.

Correct: (D)

Sulfur has 16 electrons: 2 in the first shell, 8 in the second shell and 6 in the third shell, giving 2,8,6.

Correct: (B)

The atom gains one electron to form Cl-, so the ion has 17 + 1 = 18 electrons.

Correct: (C)

In ionic bonding, metal atoms lose electrons and non-metal atoms gain them; the resulting positive and negative ions are held together by electrostatic attraction.

Correct: (C)

In graphite each carbon atom forms three covalent bonds, so the fourth outer electron is delocalised and free to move through the layers, carrying an electric current.

Correct: (A)

An oxygen molecule contains a double bond (O=O); methane, ammonia and hydrogen contain only single bonds.

Correct: (D)

The regular layers of metal ions can slide into new positions without the structure breaking apart, which makes metals malleable.

Correct: (B)

Moles = mass / Mr = 8.0 / 16 = 0.50 mol.

Correct: (D)

Volume = moles × 24 dm^3 = 0.25 × 24 = 6.0 dm^3.

Correct: (B)

Moles of C = 80 / 12 = 6.67; moles of H = 20 / 1 = 20. The ratio C : H = 6.67 : 20 = 1 : 3, so the empirical formula is CH3.

Correct: (C)

Percentage yield = (actual yield / theoretical yield) × 100 = (30 / 40) × 100 = 75%.

Correct: (A)

250 cm^3 = 0.250 dm^3. Concentration = moles / volume = 0.50 / 0.250 = 2.0 mol/dm^3.

Correct: (A)

Moles of CaCO3 = 10 / 100 = 0.10 mol, so 0.10 mol of CaO forms. Mass = 0.10 × 56 = 5.6 g.

Correct: (C)

42 / 14 = 3, so the molecular formula is 3 × CH2 = C3H6.

Correct: (D)

Hydrogen ions are discharged in preference to sodium ions because sodium is high in the reactivity series, so hydrogen gas is produced at the cathode.

Correct: (B)

With active copper electrodes, copper leaves the anode and is deposited on the cathode, so the cathode gains mass, the anode loses mass and the blue colour stays the same.

Correct: (B)

Negative ions are attracted to the positive electrode, which is called the anode in electrolysis.

Correct: (D)

Aluminium oxide melts at over 2000°C; dissolving it in cryolite lowers the working temperature of the electrolyte, which reduces energy costs.

Correct: (A)

Zinc is more reactive than copper, so it forms the negative terminal, loses electrons and dissolves; hydrogen is produced at the copper electrode.

Correct: (C)

Combustion releases energy to the surroundings, so it is exothermic; the other three processes take in energy.

Correct: (C)

Energy to break bonds = 436 + 242 = 678 kJ. Energy released forming bonds = 2 × 431 = 862 kJ. ΔH = 678 – 862 = -184 kJ/mol.

Correct: (B)

The activation energy is the minimum energy that colliding particles must have to react, shown as the height of the barrier above the reactants.

Correct: (D)

Thermal decomposition takes in heat energy from the surroundings, so it is endothermic; the others release energy.

Correct: (A)

In a hydrogen fuel cell, hydrogen reacts with oxygen to form water only (2H2 + O2 → 2H2O), so no carbon dioxide is emitted.

Correct: (D)

Powder exposes a much larger surface area, giving more frequent collisions between the acid and the marble, so the reaction is faster.

Correct: (A)

A catalyst offers a different route for the reaction with a lower activation energy, so more collisions are successful; it is not used up.

Correct: (C)

Because the forward reaction is exothermic, lower temperatures favour ammonia formation but make the reaction very slow; 450°C balances a reasonable yield with a reasonable rate.

Correct: (B)

Heating hydrated copper(II) sulfate drives off the water to give white anhydrous copper(II) sulfate, and adding water turns it blue again, so the change can be reversed.

Correct: (A)

The copper(II) ions gain electrons from the zinc (they are reduced), so Cu^2+ is the oxidising agent; zinc is the reducing agent.

Correct: (B)

Average rate = volume of gas / time = 90 / 30 = 3.0 cm^3/s.

Correct: (D)

There are 4 moles of gas on the left and 2 moles on the right, so higher pressure shifts the position of equilibrium towards the side with fewer gas molecules, producing more ammonia.

Correct: (C)

A weak acid such as ethanoic acid only partially splits into ions in solution, unlike a strong acid which is fully ionised.

Correct: (C)

Aluminium oxide reacts with both acids and alkalis, so it is amphoteric. Magnesium oxide is basic, and carbon and sulfur dioxide are acidic.

Correct: (D)

Ba^2+ ions from the barium chloride meet SO4^2- ions from the sodium sulfate and form insoluble barium sulfate as a white precipitate.

Correct: (A)

Carbonates react with dilute acids to release carbon dioxide, which turns limewater milky.

Correct: (B)

Sulfur dioxide is a non-metal oxide and is acidic (it forms sulfurous acid with water); the metal oxides listed are basic.

Correct: (B)

Adding excess insoluble carbonate ensures all the acid is used up; filtering removes the unreacted carbonate, and the filtrate is crystallised to obtain pure zinc sulfate.

Correct: (A)

Phenolphthalein is pink in alkaline solutions and colourless in acids.

Correct: (C)

Down the group the outer electron is in a shell further from the nucleus and is held less strongly, so it is lost more easily and the metal reacts more vigorously.

Correct: (D)

Chlorine is more reactive than bromine, so it displaces it: Cl2 + 2KBr → 2KCl + Br2, and the bromine colours the solution orange-brown.

Correct: (D)

Transition elements form coloured compounds (e.g. blue copper(II) sulfate), have high melting points and densities, and are much less reactive than Group 1 metals.

Correct: (C)

Noble gas atoms already have a full outer electron shell, so they do not need to gain, lose or share electrons.

Correct: (B)

In the reactivity series magnesium is above zinc, iron and copper, so it is the most reactive of the four.

Correct: (A)

Copper is below hydrogen in the reactivity series, so it cannot displace hydrogen from dilute acids.

Correct: (A)

Zinc is higher in the reactivity series, so it acts as a sacrificial metal and corrodes in place of the iron, even if the coating is scratched.

Correct: (D)

In an alloy, atoms of different sizes disrupt the regular arrangement, preventing the layers from sliding and making the alloy harder and stronger.

Correct: (C)

Chlorination sterilises the water by killing bacteria and other microorganisms that could cause disease.

Correct: (B)

Sulfur dioxide, released when fossil fuels containing sulfur are burned, dissolves in rainwater to form acid rain.

Correct: (B)

Each fertiliser contains 28 g of nitrogen per formula mass. Urea: 28 / 60 × 100 = 47%; ammonium nitrate: 28 / 80 = 35%; ammonium sulfate: 28 / 132 = 21%; potassium nitrate contains only 14 g of N, 14 / 101 = 14%. Urea has the highest percentage.

Correct: (C)

Alkanes have the general formula CnH2n+2. For n = 4 this gives C4H10. The others fit CnH2n and are alkenes.

Correct: (D)

Ethene has a C=C double bond and undergoes an addition reaction with bromine, so the orange colour disappears; this is the test for an unsaturated compound.

Correct: (A)

Cracking breaks long-chain alkanes into shorter, more useful alkanes and alkenes, which are used for fuels and for making polymers.

Correct: (C)

Fermentation uses enzymes in yeast at around 30°C in the absence of air, converting glucose into ethanol and carbon dioxide.

Correct: (A)

The C=C double bonds in ethene monomers open up so the molecules can join into long chains; this is addition polymerisation.

Correct: (B)

Rf = distance moved by the dye / distance moved by the solvent front = 4.0 / 8.0 = 0.50.

Correct: (D)

Barium chloride solution gives a white precipitate of barium sulfate with sulfate ions; acidifying first removes carbonate ions which would also give a white precipitate.