GCSE Chemistry Practice Test 20

Correct: (C)

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

Correct: (A)

The atomic number (proton number) defines the element; every atom of the same element has the same number of protons.

Correct: (D)

There are 7 electrons in the outer shell, so the element is in Group 7 (the halogens).

Correct: (B)

Metals lose electrons to form positive ions; losing two electrons gives an overall charge of 2+.

Correct: (A)

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

Correct: (D)

With a complete outer shell, noble gas atoms do not need to gain, lose or share electrons, so they are stable and unreactive.

Correct: (C)

(80 × 24 + 10 × 25 + 10 × 26) / 100 = (1920 + 250 + 260) / 100 = 24.3.

Correct: (B)

Transition elements form coloured compounds, have ions with different charges, and several (such as iron) are used as catalysts.

Correct: (B)

Two chloride ions are needed to balance the 2+ charge of one calcium ion, giving CaCl2.

Correct: (D)

Nitrogen and hydrogen are non-metals that share pairs of electrons, forming covalent bonds in simple molecules.

Correct: (A)

The layers in graphite are held together only by weak forces, so they slide over each other easily.

Correct: (C)

The outer electrons of metal atoms form a sea of delocalised electrons that can move and carry charge.

Correct: (B)

In the solid the ions are locked in the lattice; when molten (or dissolved) the ions can move to the electrodes and carry charge.

Correct: (D)

C60 is a spherical fullerene in which 60 carbon atoms form a hollow ball; long tubes describe nanotubes instead.

Correct: (A)

Every silicon and oxygen atom is joined by strong covalent bonds in a giant network, so a large amount of energy is needed to break it down.

Correct: (D)

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

Correct: (C)

Moles = mass / Mr = 11 / 44 = 0.25 mol.

Correct: (B)

Moles = concentration × volume in dm^3 = 0.4 × 0.025 = 0.01 mol.

Correct: (A)

500 cm^3 = 0.5 dm^3, so concentration = 20 / 0.5 = 40 g/dm^3.

Correct: (D)

Percentage yield = (4.5 / 6.0) × 100 = 75%.

Correct: (C)

Atom economy = (80 / 124) × 100 = 64.5%, approximately 65%.

Correct: (B)

0.1 mol of Mg produces 0.1 mol of H2; volume = 0.1 × 24 = 2.4 dm^3.

Correct: (A)

Metal + acid → salt + hydrogen; hydrochloric acid gives chloride salts.

Correct: (D)

Alkalis are soluble bases that release hydroxide ions, OH^-, in solution, giving pH values above 7.

Correct: (C)

Excess insoluble base is added to warm acid, the leftover solid is filtered off, and the filtrate is then crystallised.

Correct: (B)

Cryolite lowers the melting point (to about 950°C), reducing the energy needed compared with melting pure aluminium oxide at over 2000°C.

Correct: (A)

Potassium is near the top of the reactivity series and reacts very vigorously with cold water; copper is near the bottom.

Correct: (D)

Iron is higher in the reactivity series, so it displaces copper: Fe + CuSO4 → FeSO4 + Cu.

Correct: (C)

Hydroxide ions from the water are discharged at the anode to give oxygen; copper forms at the cathode.

Correct: (B)

Reduction is the gain of electrons (OILRIG: Oxidation Is Loss, Reduction Is Gain).

Correct: (C)

Thermal decomposition takes in energy from the surroundings to break the compound down, so it is endothermic; combustion and neutralisation are exothermic.

Correct: (B)

Energy to break bonds = 941 + (3 × 436) = 2249; energy released forming bonds = 6 × 391 = 2346; ΔH = 2249 – 2346 = -97 kJ/mol.

Correct: (D)

In an exothermic reaction the products sit lower on the energy diagram than the reactants; the difference is given out as heat.

Correct: (A)

Fuel cells are fed with hydrogen and oxygen from external supplies, so they keep working while fuel is supplied, producing only water.

Correct: (C)

Passing a current from a charger reverses the cell reactions, restoring the original reactants so the battery can be used again.

Correct: (B)

Mean rate = 100 / 25 = 4 cm^3/s.

Correct: (D)

A higher concentration means particles are closer together, giving more frequent collisions and a faster rate.

Correct: (A)

The gradient of the graph is the rate, so the steepest initial gradient shows the fastest reaction.

Correct: (C)

Raising the temperature favours the endothermic (backward) reaction, so the equilibrium moves left and less SO3 is present.

Correct: (B)

An increase in temperature always favours the endothermic direction, so here equilibrium shifts to the right.

Correct: (D)

A catalyst speeds up the forward and backward reactions equally, so equilibrium is reached sooner but its position is unchanged.

Correct: (A)

The column is hottest at the bottom and coolest at the top, so the lowest-boiling fractions rise highest before condensing.

Correct: (C)

Alkenes fit the general formula CnH2n; for n = 3 this gives C3H6. The others are alkanes (CnH2n+2).

Correct: (D)

Cracking breaks long alkanes into shorter, more useful alkanes plus alkenes, e.g. C10H22 → C6H14 + C4H8.

Correct: (A)

The ester takes its first name from the alcohol (ethyl from ethanol) and its second name from the carboxylic acid (ethanoate from ethanoic acid).

Correct: (C)

In condensation polymerisation, monomers join together and lose small molecules such as water, as in the formation of polyesters.

Correct: (D)

Complete combustion: CH4 + 2O2 → CO2 + 2H2O.

Correct: (B)

Formulations are mixtures mixed in carefully measured quantities so that the product has the required properties.

Correct: (A)

Rf = 3.6 / 9.0 = 0.4.

Correct: (D)

Hydrogen burns with a squeaky pop when a lit splint is held at the mouth of the tube.

Correct: (C)

Sulfate ions form a white precipitate of barium sulfate with barium chloride solution (the acid removes carbonate ions that would also give a white precipitate).

Correct: (A)

Air contains about 21% oxygen, 78% nitrogen and small amounts of argon (about 1%) and carbon dioxide (about 0.04%).

Correct: (C)

Intense volcanic activity released gases, so the early atmosphere was mostly carbon dioxide with little or no oxygen, similar to Mars and Venus today.

Correct: (B)

Carbon dioxide dissolved in the oceans and was taken up by organisms; their remains formed sedimentary rocks such as limestone and fossil fuels.

Correct: (A)

Carbon monoxide is a colourless, odourless, toxic gas that binds to haemoglobin and prevents the blood carrying enough oxygen.

Correct: (C)

Waste water is screened, then sedimentation separates sludge from effluent, which is treated by aerobic biological processes.

Correct: (B)

Plants absorb copper compounds from low-grade ores and concentrate them; the ash from burning the harvested plants is rich in copper. Using bacteria describes bioleaching instead.

Correct: (D)

Rusting needs both water and oxygen; iron kept in only one of them does not rust, which is why barrier coatings and galvanising work.

Correct: (A)

NPK fertilisers contain compounds of nitrogen (N), phosphorus (P) and potassium (K), the three elements plants need in the largest amounts.

Correct: (B)

Desalination works but needs a lot of energy, making it expensive and impractical in many places; the water produced is safe and drinkable.