GCSE Chemistry Practice Test 4

Correct: (C)

The nucleus contains the protons and neutrons, which account for almost all of the atom's mass; electrons have almost no mass.

Correct: (A)

19 electrons fill the shells as 2, then 8, then 8, leaving 1 electron in the fourth shell.

Correct: (D)

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

Correct: (B)

The group number equals the number of electrons in the outer shell; 7 outer electrons means Group 7 (the halogens).

Correct: (A)

Atomic (proton) number is the number of protons in the nucleus, and it defines which element the atom is.

Correct: (D)

Newlands forced elements into groups of eight without leaving gaps, so dissimilar elements (including metals and non-metals) ended up grouped together.

Correct: (B)

Mass number = protons + neutrons, the total number of particles in the nucleus.

Correct: (C)

Chemical properties depend on the electron arrangement, which is the same for isotopes of an element; only the neutron number differs.

Correct: (D)

Covalent bonding involves pairs of electrons shared between atoms, usually non-metal atoms.

Correct: (B)

When a simple molecular substance boils, only the weak forces between molecules are broken; the strong covalent bonds inside the molecules stay intact.

Correct: (C)

The giant ionic lattice is held together by strong attractions in all directions, so a lot of thermal energy is needed to break the structure.

Correct: (A)

Graphene is a sheet of carbon atoms only one atom thick, separated from graphite; it is strong and conducts electricity.

Correct: (B)

The regular layers of positive ions in a metal can slide over one another while the delocalised electrons hold the structure together.

Correct: (C)

Thermosoftening polymers have tangled chains held by weak intermolecular forces, so heating lets the chains slide apart; thermosetting polymers have cross-links and do not soften.

Correct: (A)

Nanoparticles have a huge surface area to volume ratio, giving many exposed atoms that can take part in reactions.

Correct: (D)

Mr = 23 + 16 + 1 = 40.

Correct: (A)

Moles = mass / Ar = 5.6 / 56 = 0.1 mol.

Correct: (B)

Moles of Zn = 6.5 / 65 = 0.1 mol, so 0.1 mol of ZnCl2 forms. Mass = 0.1 × 136 = 13.6 g.

Correct: (D)

500 cm^3 = 0.5 dm^3. Concentration = 20 / 0.5 = 40 g/dm^3.

Correct: (C)

There are 2 nitrogen atoms: mass of N = 2 × 14 = 28. Percentage = 28 / 80 × 100 = 35%.

Correct: (C)

Moles of HCl = 0.10 × (20.0 / 1000) = 0.0020 mol, so 0.0020 mol of NaOH is in 25.0 cm^3. Concentration = 0.0020 / 0.025 = 0.080 mol/dm^3.

Correct: (D)

Atom economy = 95 / (95 + 2) × 100 = 95 / 97 × 100 ≈ 98%.

Correct: (B)

Universal indicator is purple in strong alkali, green in neutral solutions and red in strong acid.

Correct: (A)

Metal + acid → salt + hydrogen, so zinc + sulfuric acid gives zinc sulfate and hydrogen.

Correct: (D)

Copper is less reactive than hydrogen, so copper ions (Cu^2+) are discharged at the cathode and copper metal coats the electrode.

Correct: (A)

Hydroxide ions are discharged at the anode to form oxygen and water (there are no halide ions present).

Correct: (C)

Metals below carbon in the reactivity series can be extracted by reduction with carbon; carbon takes the oxygen from the iron oxide.

Correct: (B)

Each magnesium atom loses two electrons to form Mg^2+; loss of electrons is oxidation (OILRIG).

Correct: (B)

Acid strength describes the proportion of molecules that ionise: strong acids ionise completely, weak acids (e.g. ethanoic acid) only partially.

Correct: (D)

Chloride ions are present in high concentration, so they are discharged at the anode to form chlorine gas.

Correct: (A)

Thermal decomposition takes in energy from the surroundings; combustion, neutralisation and freezing are all exothermic.

Correct: (C)

Energy to break bonds = 436 + 193 = 629 kJ. Energy released forming bonds = 2 × 366 = 732 kJ. Overall change = 629 – 732 = -103 kJ/mol (exothermic).

Correct: (A)

The activation energy is the minimum energy particles need to react, shown as the height from the reactant level to the peak of the profile.

Correct: (C)

In an exothermic reaction energy is released to the surroundings, so the products end up at a lower energy level than the reactants.

Correct: (B)

In a hydrogen fuel cell, hydrogen reacts with oxygen to produce water only: 2H2 + O2 → 2H2O.

Correct: (D)

Powdering increases the surface area exposed to the acid, so there are more frequent collisions and a faster rate.

Correct: (D)

Mean rate = quantity of product formed / time taken = 100 / 50 = 2 cm^3/s.

Correct: (B)

A higher concentration means more reacting particles in a given volume, leading to more frequent collisions.

Correct: (C)

At equilibrium the rates of the forward and backward reactions are equal, so concentrations stop changing (they are not necessarily equal).

Correct: (B)

There are 2 gas molecules on the left and 4 on the right; increasing pressure shifts equilibrium towards the side with fewer molecules, the left.

Correct: (D)

A catalyst speeds up the forward and reverse reactions equally, so the position of equilibrium and the yield are unchanged.

Correct: (A)

Longer molecules have stronger intermolecular forces, giving higher boiling points, greater viscosity and lower flammability.

Correct: (C)

Cracking (using a catalyst or steam at high temperature) splits long-chain alkanes into shorter alkanes and alkenes to meet demand.

Correct: (D)

Alkenes contain one C=C double bond and have the general formula CnH2n; ethene is C2H4.

Correct: (C)

Carboxylic acids contain the -COOH functional group; ethanoic acid is CH3COOH and is the acid in vinegar.

Correct: (B)

Oxidation of ethanol produces ethanoic acid, which is why wine left open to the air tastes sour (vinegary).

Correct: (D)

In condensation polymerisation, each new bond formed releases a small molecule, usually water, as when a diol and a dicarboxylic acid form a polyester.

Correct: (A)

Hydrogen burns rapidly in air with a characteristic squeaky pop when tested with a lighted splint.

Correct: (A)

Carbon dioxide reacts with limewater (calcium hydroxide solution) to form insoluble calcium carbonate, turning it milky.

Correct: (D)

Flame emission spectroscopy is rapid, sensitive and accurate, and can detect several elements in a mixture and find their concentrations.

Correct: (B)

Silver chloride is insoluble and forms a white precipitate; (silver bromide is cream and silver iodide is yellow).

Correct: (B)

Today's atmosphere is about 78% nitrogen, 21% oxygen, and small amounts of argon, carbon dioxide and other gases.

Correct: (D)

Photosynthesising algae (later plants) released oxygen over billions of years, while the carbon dioxide level fell.

Correct: (B)

Coal, oil and gas contain carbon stored since the organisms died millions of years ago; combustion converts it to CO2, adding to the atmosphere.

Correct: (C)

Carbon particulates reflect sunlight (global dimming) and can be inhaled, causing respiratory and health problems; sulfur dioxide, not particulates, causes acid rain.

Correct: (B)

Anaerobic digestion of sludge by microorganisms produces biogas containing methane, used as a fuel; the remaining solid can be used as fertiliser.

Correct: (A)

NPK fertilisers contain compounds of nitrogen (N), phosphorus (P) and potassium (K) in proportions suited to different crops.

Correct: (A)

Nitrogen is obtained from the air and hydrogen mainly from natural gas; they react over an iron catalyst at about 450 °C and 200 atmospheres.

Correct: (B)

In phytomining, plants absorb metal compounds as they grow; burning the harvested plants gives ash rich in the metal. (Using bacteria describes bioleaching instead.)

Correct: (D)

An LCA evaluates impacts at each stage: extracting raw materials, manufacture, use, and disposal; some stages involve value judgements, so LCAs are not purely objective.