GCSE Chemistry Practice Test 12

Correct: (A)

The proton number is the atomic number; element 17 is chlorine.

Correct: (C)

The mass number (nucleon number) is the total number of protons and neutrons in the nucleus.

Correct: (D)

Halogens become less reactive down the group because the outer shell is further from the nucleus, so it is harder to gain an extra electron.

Correct: (B)

Calcium's 20 electrons fill the shells as 2, 8, 8, 2, placing calcium in Group 2.

Correct: (A)

Thomson proposed that the atom was a ball of positive charge with negative electrons embedded in it, like plums in a pudding.

Correct: (D)

Electrons have a relative charge of -1 and a very small relative mass.

Correct: (C)

Relative atomic mass = (24 × 79 + 25 × 10 + 26 × 11) / 100 = (1896 + 250 + 286) / 100 = 2432 / 100 = 24.32, approximately 24.3.

Correct: (B)

Newlands' law of octaves was an early attempt at a periodic table, though it broke down for heavier elements.

Correct: (B)

Ionic compounds conduct only when their ions are free to move, which happens when molten or in solution.

Correct: (A)

Polymers are long chains of repeating units joined by covalent bonds; the weak forces between chains mean they usually have low melting points.

Correct: (C)

Silica has a giant covalent structure like diamond, in which every atom is held by strong covalent bonds.

Correct: (D)

In an alloy, atoms of different sizes disrupt the regular layers, preventing them from sliding, which makes the metal harder.

Correct: (B)

A covalent bond is a shared pair of electrons between atoms of non-metal elements.

Correct: (A)

Graphene is one layer of graphite; it is extremely strong for its weight and conducts electricity because it has delocalised electrons. (The hollow sphere is a fullerene.)

Correct: (A)

Ionic lattices are held together by strong electrostatic forces in all directions, so lots of thermal energy is needed to break them down.

Correct: (C)

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

Correct: (A)

Mass = moles × Mr = 2 × 18 = 36 g.

Correct: (D)

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

Correct: (B)

Percentage yield = (8 / 10) × 100 = 80%.

Correct: (C)

Atom economy = (40 / 84) × 100 = 47.6%.

Correct: (A)

Volume = moles × 24 = 0.25 × 24 = 6 dm^3.

Correct: (B)

Moles = concentration × volume in dm^3 = 0.100 × (25.0 / 1000) = 0.100 × 0.025 = 0.0025 mol.

Correct: (B)

Universal indicator turns blue to purple in alkaline solutions (high pH).

Correct: (D)

Insoluble salts are made by precipitation: mix two soluble salts, filter off the solid, wash it with distilled water and dry it.

Correct: (A)

Copper is less reactive than hydrogen, so copper is discharged at the cathode; hydroxide ions are discharged at the anode to give oxygen.

Correct: (C)

Calcium reacts with cold water to form calcium hydroxide and hydrogen; copper and gold do not react, and lead reacts only very slowly.

Correct: (B)

Pure water and neutral solutions have pH 7; acids are below 7 and alkalis are above 7.

Correct: (D)

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

Correct: (A)

In the molten salt the only positive ions are K^+, which gain electrons at the cathode to form potassium metal.

Correct: (C)

Methyl orange changes colour at the end point of a strong acid-weak alkali titration; a suitable indicator must change within the pH jump at the end point.

Correct: (C)

An endothermic reaction takes in energy from the surroundings, so their temperature decreases.

Correct: (A)

Bonds broken = 945 + (3 × 436) = 945 + 1308 = 2253 kJ/mol. Bonds formed = 6 × 391 = 2346 kJ/mol. Overall change = 2253 – 2346 = -93 kJ/mol, so the reaction is exothermic.

Correct: (B)

The voltage of a simple cell depends on the metals used; a bigger difference in reactivity gives a bigger voltage.

Correct: (D)

In an exothermic reaction the products have less energy than the reactants; the difference is released to the surroundings.

Correct: (C)

A non-rechargeable cell stops when one reactant is consumed and the reaction can no longer take place.

Correct: (A)

A higher concentration means more reacting particles in the same volume, so successful collisions occur more often.

Correct: (D)

Mean rate = change in mass / time = 1.2 / 60 = 0.02 g/s.

Correct: (B)

A catalyst increases the rates of both directions equally, so equilibrium is reached faster but its position is unchanged.

Correct: (C)

Increasing the temperature favours the endothermic direction, which here is the reverse reaction, so the equilibrium yield of ammonia falls (although the rate is faster).

Correct: (A)

The line levels off when no more gas is produced, meaning the reaction is complete and a reactant has run out.

Correct: (D)

Higher pressure puts more particles into the same volume, increasing the frequency of collisions.

Correct: (B)

Crude oil is a finite resource and a mixture of many different hydrocarbon compounds, which is why it can be separated by fractional distillation.

Correct: (C)

Alkenes are unsaturated hydrocarbons containing a C=C double bond, with general formula CnH2n.

Correct: (A)

Complete combustion of a hydrocarbon produces carbon dioxide and water: CH4 + 2O2 → CO2 + 2H2O.

Correct: (D)

The hydration of ethene to ethanol uses steam at about 300 °C and high pressure with a phosphoric acid catalyst.

Correct: (B)

Carboxylic acids contain the -COOH functional group; for example, ethanoic acid is CH3COOH. They react with carbonates to give carbon dioxide.

Correct: (C)

In condensation polymerisation (for example making a polyester from a diol and a dicarboxylic acid), monomers join and a small molecule like water is eliminated.

Correct: (D)

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

Correct: (A)

Chlorine bleaches damp litmus paper (it may first turn red, then white).

Correct: (B)

Barium chloride gives a white precipitate of barium sulfate with sulfate ions; the acid is added first to remove any carbonate that would also give a white precipitate.

Correct: (C)

A pure substance produces only one spot in chromatography; a mixture would separate into several spots.

Correct: (B)

Nitrogen makes up about 78% of the modern atmosphere, oxygen about 21%, and the rest is mostly argon with a little carbon dioxide.

Correct: (A)

Carbon dioxide dissolved in the oceans (forming carbonate sediments and shells) and was absorbed by algae and plants during photosynthesis, which also released oxygen.

Correct: (D)

Carbon monoxide is a toxic, colourless, odourless gas that combines with haemoglobin, preventing it from carrying oxygen around the body.

Correct: (C)

Particulates reflect sunlight (global dimming) and can be inhaled, causing breathing problems and other health issues.

Correct: (D)

Sterilising agents such as chlorine (or ozone and ultraviolet light) are used to make sure potable water contains very few microbes.

Correct: (A)

In bioleaching, bacteria produce a leachate solution containing metal compounds from low-grade ores, from which the metal can then be extracted.

Correct: (D)

Crude oil is a finite resource that will eventually run out; it is used for fuels and as a raw material for petrochemicals.

Correct: (B)

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

Correct: (C)

Using renewable energy and reducing wasted energy lowers the amount of carbon dioxide released, reducing the carbon footprint.