GCSE Chemistry Practice Test 13

Correct: (A)

A neutron has no charge (relative charge 0); a proton is +1 and an electron is -1.

Correct: (B)

Number of neutrons = mass number – atomic number = 23 – 11 = 12.

Correct: (C)

The 12 electrons fill the shells as 2 in the first, 8 in the second and 2 in the third: 2,8,2.

Correct: (D)

Chemical properties depend on electron arrangement; isotopes differ only in their number of neutrons.

Correct: (B)

Mendeleev left gaps for undiscovered elements and even predicted the properties of the elements that would fill them.

Correct: (C)

Down the group the outer electron is further from the nucleus and less strongly attracted, so it is lost more easily.

Correct: (D)

Transition metals typically form coloured compounds, have high densities, and many act as catalysts.

Correct: (A)

Alpha particles scattered by gold foil showed that atoms have a tiny, dense, positively charged nucleus.

Correct: (C)

Sodium chloride is a regular lattice of Na^+ and Cl^- ions held together by strong electrostatic attractions.

Correct: (D)

Each carbon atom forms four covalent bonds, leaving no free electrons or ions to carry a charge.

Correct: (A)

Only weak intermolecular forces need to be overcome to melt or boil them, so little energy is required.

Correct: (B)

Carbon atoms bond strongly within each layer, but weak forces between the layers let them slide over each other.

Correct: (D)

The layers of metal atoms can slide but stay bonded through the delocalised electrons, so the metal does not break.

Correct: (A)

Nanoparticles have diameters between about 1 nm and 100 nm, only a few hundred atoms across.

Correct: (B)

Silicon dioxide (sand) is a giant lattice of silicon and oxygen atoms joined by covalent bonds.

Correct: (C)

Mr = 40 + 2 × (16 + 1) = 40 + 34 = 74.

Correct: (A)

Moles = mass / Mr = 8 / 16 = 0.5 mol.

Correct: (C)

Moles of Mg = 6 / 24 = 0.25 mol, so moles of MgO = 0.25 mol; mass = 0.25 × 40 = 10 g.

Correct: (B)

500 cm^3 = 0.5 dm^3, so concentration = 10 / 0.5 = 20 g/dm^3.

Correct: (D)

Percentage yield = (actual yield / theoretical yield) × 100 = (36 / 45) × 100 = 80%.

Correct: (B)

Atom economy = 95 / (24 + 2 × 36.5) × 100 = (95 / 97) × 100 = about 98%.

Correct: (D)

Volume = moles × 24 = 0.25 × 24 = 6 dm^3.

Correct: (A)

Strong alkalis have high pH values, typically around 13 to 14.

Correct: (C)

Acid + metal carbonate → salt + water + carbon dioxide.

Correct: (C)

Filtration removes the unreacted copper(II) oxide; the filtrate is then crystallised to obtain pure salt crystals.

Correct: (A)

Strong acids fully ionise in water, for example HCl → H^+ + Cl^-.

Correct: (D)

Positive lead ions move to the cathode and are discharged: Pb^2+ + 2e^- → Pb.

Correct: (B)

Because sodium is high in the reactivity series, H^+ ions are preferentially discharged at the cathode to give hydrogen.

Correct: (D)

Magnesium is the most reactive of these metals, so it fizzes most vigorously with the acid.

Correct: (B)

Dissolving aluminium oxide in molten cryolite lowers the working temperature from over 2000°C, saving a lot of energy.

Correct: (C)

Exothermic reactions transfer energy to the surroundings, so the temperature of the surroundings rises.

Correct: (A)

Particles must collide with at least the activation energy for bonds to break and a reaction to happen.

Correct: (A)

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

Correct: (D)

The greater the difference in reactivity between the two electrode metals, the greater the voltage produced.

Correct: (B)

In the fuel cell hydrogen reacts with oxygen, 2H2 + O2 → 2H2O, producing water only.

Correct: (C)

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

Correct: (B)

A higher concentration means the particles are closer together, so they collide more often.

Correct: (A)

A catalyst offers a different pathway that needs less energy, and it is not used up in the reaction.

Correct: (D)

Larger chips have a smaller surface area, so collisions happen less frequently and the rate falls.

Correct: (C)

There are 4 molecules on the left and only 2 on the right, so higher pressure favours the right-hand side.

Correct: (C)

Raising the temperature favours the endothermic direction, which absorbs some of the extra energy.

Correct: (B)

Fractional distillation separates the hydrocarbons in crude oil according to their different boiling points.

Correct: (A)

Alkenes have the general formula CnH2n; the alkanes are CnH2n+2.

Correct: (D)

Alkenes decolourise bromine water because bromine adds across the C=C double bond.

Correct: (D)

Cracking breaks long chains into smaller, more useful alkanes together with alkenes.

Correct: (C)

Enzymes in yeast ferment glucose to ethanol and carbon dioxide under warm, anaerobic conditions.

Correct: (B)

Many ethene molecules join together by addition polymerisation to form poly(ethene).

Correct: (A)

A pure substance melts at a specific temperature; impurities lower the melting point and make melting happen over a range.

Correct: (A)

Rf = distance moved by the substance / distance moved by the solvent = 4 / 8 = 0.5.

Correct: (B)

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

Correct: (D)

Potassium gives a lilac flame; sodium is yellow, lithium is crimson and copper is green.

Correct: (C)

Air is about 78% nitrogen, 21% oxygen, about 0.9% argon and 0.04% carbon dioxide.

Correct: (B)

Methane and carbon dioxide are greenhouse gases; they absorb infrared radiation radiated by the Earth.

Correct: (D)

Carbon dioxide dissolved in the oceans and was trapped in carbonate sediments, shells and eventually fossil fuels.

Correct: (C)

Sulfur dioxide dissolves in rainwater to form acid rain, which damages buildings, trees and lakes.

Correct: (A)

Chlorine is added to potable water to kill harmful microorganisms; the other options are separation methods that do not sterilise water.

Correct: (C)

The plants absorb metal compounds from the soil, and the ash left after burning contains the metal compound in a concentrated form.

Correct: (A)

An LCA covers obtaining raw materials, manufacture, use, and disposal of a product.

Correct: (D)

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

Correct: (B)

Recycling conserves finite ore supplies and typically uses far less energy than extraction from ores.