GCSE Chemistry Practice Test 19

Correct: (B)

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

Correct: (C)

The neutron sits in the nucleus and carries no charge; the proton is positive and electrons are found in shells outside the nucleus.

Correct: (A)

The group number equals the number of electrons in the outer shell, which is 1.

Correct: (D)

Isotopes have the same number of protons but different numbers of neutrons, so they have different mass numbers.

Correct: (B)

Elements in the same group have the same number of outer-shell electrons, so they react in similar ways.

Correct: (A)

The period number equals the number of electron shells, and this atom has three shells.

Correct: (D)

(75 × 35 + 25 × 37) / 100 = (2625 + 925) / 100 = 35.5.

Correct: (C)

Mendeleev left gaps for elements not yet discovered and correctly predicted their properties; elements were arranged by atomic mass, not atomic number.

Correct: (D)

Magnesium atoms transfer electrons to oxygen atoms, forming Mg^2+ and O^2- ions held together by electrostatic attraction.

Correct: (A)

Water is made of small H2O molecules with covalent bonds inside each molecule; the others are giant ionic, giant covalent or metallic structures.

Correct: (C)

Sodium chloride is a giant ionic lattice, and the strong electrostatic attractions between oppositely charged ions need a lot of energy to break.

Correct: (B)

Each carbon atom in graphite bonds to three others, leaving one delocalised electron per atom that can carry charge.

Correct: (D)

Low melting and boiling points and no electrical conductivity are typical of simple molecules with weak intermolecular forces.

Correct: (A)

Nanoparticles have diameters between 1 nm and 100 nm and contain only a few hundred atoms.

Correct: (C)

In a metal the regular layers of positive ions can slide over each other while the delocalised electrons still hold the structure together.

Correct: (A)

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

Correct: (D)

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

Correct: (B)

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

Correct: (C)

250 cm^3 = 0.25 dm^3, so concentration = 0.5 / 0.25 = 2 mol/dm^3.

Correct: (A)

Percentage yield = (16 / 20) × 100 = 80%.

Correct: (D)

Atom economy = (56 / 100) × 100 = 56%.

Correct: (B)

Volume = 0.25 × 24 = 6 dm^3.

Correct: (C)

Acids release H^+ ions in aqueous solution, which is why they share the same reactions.

Correct: (B)

Neutralisation: acid + alkali → salt + water.

Correct: (D)

Sulfuric acid always forms sulfate salts, so the product is copper sulfate (plus water).

Correct: (A)

Positive lead ions (Pb^2+) move to the cathode, gain electrons and form lead metal.

Correct: (C)

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

Correct: (B)

Sodium is very reactive, so hydrogen ions from the water are discharged at the cathode to give hydrogen gas.

Correct: (D)

Metals below carbon in the reactivity series can be extracted by reduction with carbon.

Correct: (A)

The indicator changes colour at the end point, showing when neutralisation is just complete.

Correct: (B)

The process takes in energy from the surroundings, so the temperature decreases; this is endothermic.

Correct: (D)

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

Correct: (A)

Activation energy is the extra energy reactants need to reach the top of the energy barrier before they can react.

Correct: (C)

In a hydrogen fuel cell, hydrogen + oxygen → water, and the chemical energy is converted directly to electrical energy.

Correct: (B)

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

Correct: (D)

Mean rate = 90 / 30 = 3 cm^3/s.

Correct: (A)

At higher temperatures particles move faster and have more energy, so collisions are more frequent and more of them are successful.

Correct: (C)

A catalyst gives the reacting particles a route with a lower activation energy, and it is not used up.

Correct: (B)

Powder exposes a much larger surface area, so acid particles collide with the marble more often.

Correct: (D)

There are 4 molecules of gas on the left and 2 on the right, so higher pressure favours the right-hand side and more ammonia forms.

Correct: (A)

At equilibrium the forward and backward reactions continue at the same rate, so concentrations stay constant.

Correct: (C)

Each fraction condenses at a different height in the column because its hydrocarbons boil and condense over different temperature ranges.

Correct: (B)

Alkanes fit the general formula CnH2n+2; for n = 3 this gives C3H8. The others fit CnH2n and are alkenes.

Correct: (D)

Alkenes contain a C=C double bond and react with bromine, turning orange bromine water colourless; alkanes do not react.

Correct: (A)

Yeast enzymes convert glucose to ethanol and carbon dioxide in the absence of air at around 30-40°C.

Correct: (C)

Carboxylic acids react with carbonates to give a salt, carbon dioxide and water.

Correct: (B)

Many ethene monomers join together by opening their double bonds, with no other product formed; this is addition polymerisation.

Correct: (A)

Pure substances melt and boil at specific temperatures; impurities lower the melting point and cause melting over a range.

Correct: (D)

Rf = distance moved by dye / distance moved by solvent, so distance = 0.6 × 10 = 6 cm.

Correct: (B)

Chlorine is identified because it bleaches damp litmus paper (it first turns it red, then white).

Correct: (C)

Lithium compounds give a crimson red flame; sodium gives yellow, potassium lilac and copper green.

Correct: (D)

Air is about 78% nitrogen, 21% oxygen, about 1% argon and 0.04% carbon dioxide.

Correct: (A)

Methane absorbs long-wave radiation from the Earth and re-radiates it, contributing to the greenhouse effect, as does carbon dioxide.

Correct: (B)

Photosynthesis by algae and plants removed carbon dioxide and released oxygen, while much carbon dioxide also dissolved in the oceans and became locked in rocks.

Correct: (C)

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

Correct: (B)

Sterilising agents such as chlorine kill microbes and make the water safe to drink; grit is removed earlier by filtration.

Correct: (C)

Bacteria produce solutions (leachate) containing copper compounds, from which copper can then be extracted; using plants describes phytomining instead.

Correct: (A)

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

Correct: (D)

The Haber process uses about 450°C, 200 atmospheres pressure and an iron catalyst, chosen as a compromise between rate and yield.

Correct: (C)

Extracting aluminium needs huge amounts of electricity for electrolysis, while melting and recycling scrap aluminium uses only a small fraction of that energy.