GCSE Chemistry Practice Test 3

Correct: (B)

The neutron has no charge and a relative mass of 1; a proton has charge +1 and an electron has charge -1 with almost zero mass.

Correct: (C)

Neutrons = mass number – atomic number = 23 – 11 = 12.

Correct: (A)

Isotopes have the same atomic number (protons) but different mass numbers because their nuclei contain different numbers of neutrons.

Correct: (D)

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

Correct: (B)

Mendeleev left gaps for undiscovered elements and correctly predicted their properties, which is why his table was accepted.

Correct: (A)

Down the group the outer electron is in a shell further from the nucleus and is shielded more, so it is lost more easily and reactions are more vigorous.

Correct: (C)

The atom gains one electron to form the negative ion: 17 + 1 = 18 electrons.

Correct: (D)

Transition elements form coloured compounds and their ions can have variable charges, unlike Group 1 metals.

Correct: (A)

Ionic compounds conduct when their ions are free to move, which happens when the compound is molten or dissolved, not in the solid lattice.

Correct: (B)

In diamond every carbon atom is joined to four others by strong covalent bonds in a rigid giant lattice, so a large force is needed to break it.

Correct: (C)

Each carbon atom in graphite forms three bonds, leaving one delocalised electron per atom that is free to move and carry charge.

Correct: (D)

Fullerenes are molecules of carbon atoms arranged in closed cages; C60 forms a spherical cage of hexagonal and pentagonal rings.

Correct: (B)

Metallic bonding is the strong electrostatic attraction between positive metal ions and the delocalised electrons around them.

Correct: (A)

Nanoparticles are structures between 1 nm and 100 nm in size, containing a few hundred atoms.

Correct: (B)

In a pure metal the regular layers slide easily; in an alloy, different-sized atoms disrupt the layers and stop them sliding, making the alloy harder.

Correct: (C)

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

Correct: (A)

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

Correct: (D)

Moles of Mg = 4.8 / 24 = 0.2 mol, so 0.2 mol of MgO is formed. Mass = 0.2 × 40 = 8.0 g.

Correct: (B)

Volume = 250 cm^3 = 0.250 dm^3. Concentration = 0.50 / 0.250 = 2.0 mol/dm^3.

Correct: (C)

Percentage yield = (32 / 40) × 100 = 80%.

Correct: (B)

Atom economy = Mr of desired product / Mr of all products × 100 = 56 / 100 × 100 = 56%.

Correct: (D)

Volume = 0.25 × 24 = 6 dm^3.

Correct: (C)

pH 7 is neutral; below 7 is acidic and above 7 is alkaline.

Correct: (D)

Acid + metal carbonate → salt + water + carbon dioxide, so the products are calcium chloride, water and carbon dioxide.

Correct: (A)

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

Correct: (C)

At the cathode the less reactive element is discharged; hydrogen is less reactive than sodium, so H^+ ions form hydrogen gas and sodium stays in solution.

Correct: (C)

A more reactive metal displaces a less reactive metal from its compound; zinc is above copper in the reactivity series.

Correct: (A)

Excess insoluble base ensures every bit of acid is neutralised; the leftover solid is then removed by filtration.

Correct: (B)

Acids release hydrogen ions, H^+, in aqueous solution, and it is these ions that make solutions acidic.

Correct: (C)

Aluminium oxide melts at over 2000 °C; dissolving it in cryolite lowers the working temperature and greatly reduces the energy cost.

Correct: (D)

In an exothermic reaction energy is transferred to the surroundings, so the temperature of the surroundings increases.

Correct: (A)

Energy to break bonds = 436 + 242 = 678 kJ. Energy released forming bonds = 2 × 431 = 862 kJ. Overall change = 678 – 862 = -184 kJ/mol (exothermic).

Correct: (B)

If the products have less energy than the reactants, the difference has been released to the surroundings, so the reaction is exothermic.

Correct: (C)

The further apart the two metals are in the reactivity series, the greater the voltage produced by the cell.

Correct: (D)

The fuel cell combines hydrogen with oxygen to form water, releasing energy as electricity.

Correct: (A)

At a higher temperature particles move faster, collide more often, and more of the collisions have enough energy to react.

Correct: (B)

A catalyst offers a different route for the reaction with a lower activation energy, so more collisions succeed; the catalyst is not used up.

Correct: (C)

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

Correct: (D)

At equilibrium both reactions continue at the same rate, so there is no overall change in the amounts of substances.

Correct: (A)

Increasing the temperature favours the endothermic (reverse) reaction, so the equilibrium moves left and less ammonia is present at equilibrium.

Correct: (B)

Increasing the pressure favours the side with fewer molecules of gas, because that side occupies a smaller volume.

Correct: (C)

Crude oil is a finite resource containing a mixture of many different hydrocarbon compounds, mainly alkanes.

Correct: (D)

Each fraction condenses at a different height in the column according to its boiling point range; shorter chains have lower boiling points and rise further.

Correct: (A)

Alkanes are saturated hydrocarbons with the general formula CnH2n+2; for example propane is C3H8.

Correct: (B)

Alkenes are unsaturated and react with bromine in an addition reaction, decolourising bromine water; alkanes do not.

Correct: (C)

Yeast enzymes convert sugars such as glucose into ethanol and carbon dioxide without oxygen, most effectively at around 37 °C.

Correct: (D)

In addition polymerisation the C=C double bonds in the monomers open up and the monomers add together to form one long polymer molecule, with no other product.

Correct: (A)

Rf = distance moved by the substance / distance moved by the solvent = 4.0 / 10.0 = 0.4.

Correct: (B)

Chlorine bleaches damp litmus paper white (it may turn red briefly first because chlorine water is acidic).

Correct: (C)

Lithium compounds give a crimson red flame (potassium gives lilac, sodium gives yellow and calcium gives orange-red).

Correct: (D)

Barium sulfate is insoluble and forms a white precipitate; the acid is added first to remove carbonate ions that would also give a white precipitate.

Correct: (A)

Volcanic activity released gases; the early atmosphere was mostly carbon dioxide, like that of Mars and Venus today, with nitrogen and water vapour.

Correct: (B)

Carbon dioxide and methane absorb infrared radiation radiated by the Earth and are the main greenhouse gases linked to human activity.

Correct: (C)

The carbon footprint measures all greenhouse gas emissions (expressed as carbon dioxide equivalents) from making, using and disposing of a product.

Correct: (D)

Sulfur dioxide, formed from sulfur impurities in fossil fuels, dissolves in rainwater to form acid rain.

Correct: (A)

Sterilising agents such as chlorine, ozone or ultraviolet light kill harmful microorganisms, making water safe to drink; insoluble solids are removed by filtration and sedimentation beforehand.

Correct: (B)

The Haber process uses a temperature of about 450 °C (a compromise for rate and yield), 200 atmospheres pressure and an iron catalyst.

Correct: (C)

An LCA assesses environmental impact when obtaining raw materials, during manufacture, during use and during disposal of the product.

Correct: (D)

Recycling uses far less energy than extracting metals from ores and preserves finite resources, as well as reducing waste and pollution.

Correct: (B)

In bioleaching, bacteria digest the ore and produce a leachate solution of metal ions, from which the metal is then obtained by displacement or electrolysis.