GCSE Chemistry Practice Test 16

Correct: (B)

Number of neutrons = mass number – atomic number = 39 – 19 = 20.

Correct: (D)

Chemical reactions depend on electron arrangement, which is the same for isotopes of an element.

Correct: (A)

13 electrons are arranged as 2 in the first shell, 8 in the second and 3 in the third.

Correct: (C)

(24 × 0.80) + (25 × 0.10) + (26 × 0.10) = 19.2 + 2.5 + 2.6 = 24.3.

Correct: (B)

A more reactive halogen displaces a less reactive halogen from a solution of its salt, forming bromine.

Correct: (D)

Elements are ordered by atomic number, and this arranges them so elements with similar properties fall into groups.

Correct: (A)

Helium is an inert noble gas, so it is safe, whereas hydrogen is highly flammable.

Correct: (C)

Lithium reacts steadily with water, forming lithium hydroxide and hydrogen gas.

Correct: (C)

The giant lattice is held together by strong electrostatic attractions between oppositely charged ions in all directions.

Correct: (A)

In a solid the ions are locked in position; when molten they are mobile and can move to the electrodes.

Correct: (D)

The strong covalent bonds within each molecule stay intact; only weak forces between molecules are broken.

Correct: (B)

C60 molecules are hollow balls of carbon atoms arranged in hexagons and pentagons.

Correct: (C)

Silicon dioxide is a giant covalent structure in which each silicon atom forms four covalent bonds to oxygen atoms.

Correct: (A)

The irregular structure of an alloy prevents the layers sliding, making it harder and stronger.

Correct: (D)

Cross-links hold the chains in a rigid three-dimensional network that does not soften on heating.

Correct: (B)

(2 × 1) + 32 + (4 × 16) = 2 + 32 + 64 = 98.

Correct: (D)

Number of molecules = 0.5 × 6.02 × 10^23 = 3.01 × 10^23.

Correct: (A)

The limiting reactant is the one that is completely used up and controls the amount of product formed.

Correct: (C)

Moles of NaOH = 0.100 × 0.0200 = 0.00200 mol = moles of HCl; concentration = 0.00200 / 0.0250 = 0.080 mol/dm^3.

Correct: (B)

Moles of CaCO3 = 5.0 / 100 = 0.050 mol, which produces 0.050 mol of CO2; mass = 0.050 × 44 = 2.2 g.

Correct: (D)

Atom economy = Mr of desired product / total Mr of all products = 65 / (65 + 28) × 100 = 70% (approximately).

Correct: (A)

Moles = 7 / 28 = 0.25 mol; volume = 0.25 × 24 = 6.0 dm^3.

Correct: (D)

Acid + metal carbonate → salt + water + carbon dioxide, so effervescence is seen.

Correct: (B)

The first run finds the volumes needed; repeating with the same volumes but no indicator gives a pure salt solution.

Correct: (C)

Metals more reactive than carbon, such as aluminium, must be extracted by electrolysis of the molten compound.

Correct: (A)

Copper is below hydrogen in the reactivity series, so Cu^2+ ions are discharged and copper metal forms at the cathode.

Correct: (D)

Water decomposes to give twice as much hydrogen as oxygen, so the volumes are in the ratio 2 : 1.

Correct: (B)

Iron displaces copper, forming iron sulfate solution and a coating of copper metal.

Correct: (C)

The pH scale is logarithmic in H^+ concentration at GCSE Higher level: each pH unit represents a factor of 10.

Correct: (A)

Cryolite lowers the working temperature from over 2000 °C, saving a great deal of energy.

Correct: (A)

Thermal decomposition takes in energy from the surroundings to break the compound down.

Correct: (C)

In exothermic reactions energy is released, so the products sit lower on the energy diagram than the reactants.

Correct: (B)

Energy to break bonds = 945 + (3 × 436) = 2253 kJ; energy released forming bonds = 6 × 391 = 2346 kJ; overall = 2253 – 2346 = -93 kJ/mol.

Correct: (D)

Energy = 100 × 4.2 × 12 = 5040 J.

Correct: (A)

The greater the difference in reactivity of the two electrodes, the greater the voltage of the cell.

Correct: (D)

The steeper the gradient of the curve (or its tangent), the faster the reaction at that moment.

Correct: (A)

A higher concentration means more particles per unit volume and therefore more frequent collisions.

Correct: (C)

A catalyst speeds up both the forward and reverse reactions equally, so equilibrium is reached faster but the yield at equilibrium is unchanged.

Correct: (B)

Sulfur forms and makes the solution cloudy; timing how long the cross takes to disappear compares the rates.

Correct: (D)

At dynamic equilibrium both reactions continue at the same rate, so the amounts of substances stay constant.

Correct: (A)

Raising the temperature favours the endothermic direction, which here is the reverse reaction, so less product is present at equilibrium.

Correct: (C)

Longer-chain hydrocarbons have higher boiling points, are more viscous and are less flammable.

Correct: (B)

With a plentiful air supply: CH4 + 2O2 → CO2 + 2H2O.

Correct: (D)

The higher carbon content of alkenes leads to incomplete combustion and a smoky, sooty flame.

Correct: (A)

Like other acids, carboxylic acids react with carbonates to give a salt, water and carbon dioxide.

Correct: (C)

Many esters have distinctive sweet smells and are used in perfumes and flavourings.

Correct: (B)

Condensation polymerisation joins monomers with the loss of small molecules, usually water.

Correct: (A)

Hydrogen burns rapidly with a squeaky pop when tested with a lit splint.

Correct: (D)

Carbon dioxide reacts with limewater to form a white precipitate of calcium carbonate.

Correct: (C)

Chloride ions give a white precipitate of silver chloride; bromide gives cream and iodide gives yellow.

Correct: (B)

Formulations are carefully measured mixtures of components, each chosen for the properties it gives the product.

Correct: (D)

Photosynthetic organisms released oxygen as a waste product over billions of years.

Correct: (A)

Dissolved carbon dioxide formed carbonates that became sediments, shells and eventually limestone rocks.

Correct: (C)

Microorganisms in the guts of cattle and in waterlogged rice fields release large amounts of methane.

Correct: (B)

Fine particulates damage lungs and reflect sunlight, reducing the amount reaching the Earth's surface.

Correct: (B)

Distillation and reverse osmosis both remove dissolved salts; they require large amounts of energy.

Correct: (C)

The ash is dissolved to give a copper compound solution, from which copper is displaced by iron or extracted by electrolysis.

Correct: (D)

Hydrogen is produced from natural gas, while the nitrogen comes from the air.

Correct: (B)

Plants need nitrogen to make proteins for growth, and ammonium nitrate provides it in a soluble form.

Correct: (C)

Reusing bottles avoids the energy costs of washing, melting and remoulding involved in recycling.