GCSE Chemistry Practice Test 15

Correct: (C)

Mass number = protons + neutrons = 11 + 12 = 23.

Correct: (B)

Isotopes are atoms of the same element (same proton number) with different numbers of neutrons.

Correct: (D)

17 electrons fill the shells as 2 in the first shell, 8 in the second and 7 in the third.

Correct: (A)

(35 × 0.75) + (37 × 0.25) = 26.25 + 9.25 = 35.5.

Correct: (B)

More shells mean more shielding and a weaker attraction, so the outer electron is lost more easily.

Correct: (C)

Mendeleev left gaps and correctly predicted the properties of elements such as germanium.

Correct: (D)

Transition metals typically form coloured compounds, have high melting points and are useful catalysts.

Correct: (A)

A stable full outer shell means noble gas atoms have no tendency to react.

Correct: (A)

Metal atoms lose electrons to form positive ions and non-metal atoms gain them to form negative ions.

Correct: (C)

A magnesium atom loses its two outer electrons, forming an Mg^2+ ion.

Correct: (B)

Carbon shares one electron pair with each of the four hydrogen atoms.

Correct: (D)

The giant covalent lattice of strong bonds makes diamond hard and gives it a very high melting point.

Correct: (A)

Each carbon atom in graphite contributes one electron to a delocalised pool that can carry charge.

Correct: (C)

The regular layers of positive ions can slide while the metallic bonding still holds the structure together.

Correct: (B)

Nanoparticles are between 1 and 100 nanometres in size, containing a few hundred atoms.

Correct: (D)

40 + 12 + (3 × 16) = 40 + 12 + 48 = 100.

Correct: (A)

Moles = mass / Mr = 8 / 40 = 0.2 mol.

Correct: (C)

12 g Mg = 12 / 24 = 0.5 mol, which forms 0.5 mol of MgO; Mr of MgO = 40, so mass = 0.5 × 40 = 20 g.

Correct: (B)

250 cm^3 = 0.25 dm^3, so concentration = 0.5 / 0.25 = 2.0 mol/dm^3.

Correct: (D)

Percentage yield = (40 / 50) × 100 = 80%.

Correct: (A)

Atom economy = (56 / 100) × 100 = 56%, because the carbon dioxide is a waste product.

Correct: (C)

Volume = 0.25 × 24 = 6.0 dm^3.

Correct: (B)

Neutralisation: acid + alkali → salt + water, as H^+ ions react with OH^- ions to form water.

Correct: (D)

A pH of 2 is well below 7, showing a strongly acidic solution with a high concentration of H^+ ions.

Correct: (A)

Filtration removes the excess solid copper oxide, leaving a pure copper sulfate solution that can be crystallised.

Correct: (C)

Positive Pb^2+ ions are attracted to the cathode, where they gain electrons and form lead metal.

Correct: (B)

In concentrated solution, chloride ions are discharged at the anode to form chlorine gas.

Correct: (D)

A more reactive metal displaces a less reactive metal from a solution of its salt.

Correct: (A)

OILRIG: Oxidation Is Loss of electrons, Reduction Is Gain of electrons.

Correct: (C)

Strong acids such as hydrochloric acid fully ionise; weak acids such as ethanoic acid only partially ionise.

Correct: (C)

Combustion releases energy to the surroundings, so the temperature of the surroundings increases.

Correct: (A)

The activation energy is the minimum energy particles must have to react, shown by the peak above the reactants.

Correct: (D)

Energy to break bonds = 436 + 243 = 679 kJ; energy released forming bonds = 2 × 431 = 862 kJ; overall = 679 – 862 = -183 kJ/mol (exothermic).

Correct: (B)

Energy = mass × specific heat capacity × temperature change = 50 × 4.2 × 8 = 1680 J.

Correct: (C)

Hydrogen is oxidised to form water, and electrical energy is produced directly rather than by burning.

Correct: (A)

Mean rate = quantity of product formed / time = 60 / 30 = 2 cm^3/s.

Correct: (D)

Higher temperature gives more frequent and more energetic collisions, so more collisions result in a reaction.

Correct: (B)

A catalyst lowers the activation energy and is not used up or chemically changed at the end.

Correct: (C)

Breaking a solid into a powder exposes more particles at the surface to collide with the acid.

Correct: (A)

There are 4 gas molecules on the left and 2 on the right, so higher pressure shifts equilibrium towards ammonia.

Correct: (D)

At equilibrium both reactions continue at equal rates, so concentrations stay constant.

Correct: (B)

Each fraction condenses at a different height in the column according to its boiling point range.

Correct: (C)

For n = 4: H = (2 × 4) + 2 = 10, so butane is C4H10.

Correct: (A)

Cracking turns less useful long-chain fractions into petrol-range alkanes and reactive alkenes.

Correct: (D)

The C=C double bond in an alkene reacts with bromine in an addition reaction, removing the orange colour.

Correct: (B)

Yeast enzymes ferment glucose to ethanol and carbon dioxide in the absence of oxygen at a warm temperature.

Correct: (C)

In addition polymerisation many ethene monomers join into long chains with no other product formed.

Correct: (D)

Impurities lower the melting point and cause melting over a range; a pure substance melts at one sharp temperature.

Correct: (A)

Rf = distance moved by substance / distance moved by solvent = 4.0 / 10.0 = 0.4.

Correct: (B)

Chlorine turns damp litmus paper red and then bleaches it white.

Correct: (C)

Barium ions react with sulfate ions to form white barium sulfate.

Correct: (A)

Today's atmosphere is roughly four-fifths nitrogen and one-fifth oxygen, with small amounts of other gases.

Correct: (D)

Volcanoes released large amounts of carbon dioxide, water vapour and nitrogen as the Earth cooled.

Correct: (B)

Greenhouse gases allow short wavelength radiation in but absorb the longer wavelength radiation radiated by the Earth.

Correct: (C)

Carbon monoxide binds strongly to haemoglobin, preventing red blood cells from carrying oxygen.

Correct: (B)

Sterilisation with chlorine (or ozone or ultraviolet light) kills microbes and makes the water safe to drink.

Correct: (D)

Bacteria growing on low-grade ores produce leachate solutions containing metal compounds such as copper ions.

Correct: (B)

An LCA considers raw materials, manufacture, use and disposal, including energy use and waste at each stage.

Correct: (A)

Melting scrap aluminium uses far less energy than extracting it from bauxite by electrolysis.

Correct: (D)

The Haber process uses a temperature of 450 °C, a pressure of 200 atmospheres and an iron catalyst.