IGCSE Chemistry Practice Test 4

Correct: (B)

Condensation is the change from a gas to a liquid, when gas particles lose energy and come closer together.

Correct: (A)

In a solid the particles are held in a regular arrangement and can only vibrate about fixed positions.

Correct: (D)

During a change of state, the energy supplied breaks forces between particles instead of raising the temperature, so the temperature stays constant.

Correct: (C)

Number of neutrons = nucleon number – proton number = 35 – 17 = 18.

Correct: (C)

The first shell holds 2 and the second holds 8, leaving 13 – 10 = 3 electrons in the third shell.

Correct: (B)

The nucleus contains protons and neutrons; the electrons are arranged in shells around the nucleus.

Correct: (A)

In graphite each carbon atom uses only three of its electrons in bonding within the layers; the fourth electron is delocalised and free to carry charge.

Correct: (D)

MgO is an ionic compound: oppositely charged ions are held in a giant lattice. It conducts electricity only when molten or aqueous, when the ions can move.

Correct: (D)

The chloride ion forms when a chlorine atom gains one electron: 17 + 1 = 18 electrons.

Correct: (C)

Chlorine exists as simple Cl2 molecules with weak intermolecular forces, so it has a low boiling point. The others have giant structures.

Correct: (B)

The configuration 2,5 means 2 electrons in the first shell and 5 electrons in the outer (second) shell.

Correct: (A)

Mr = 24 + 2 × (16 + 1) = 24 + 34 = 58.

Correct: (A)

Moles = mass / Mr = 25 / 100 = 0.25 mol.

Correct: (D)

Volume = moles × molar volume = 0.50 × 24 = 12 dm^3.

Correct: (C)

C: 40.0/12 = 3.33; H: 6.7/1 = 6.7; O: 53.3/16 = 3.33. Ratio = 1 : 2 : 1, so the empirical formula is CH2O.

Correct: (B)

Concentration = moles / volume in dm^3 = 0.20 / 0.250 = 0.80 mol/dm^3.

Correct: (C)

Percentage yield = (45 / 60) × 100 = 75%.

Correct: (A)

Moles of Mg = 4.8 / 24 = 0.20 mol, which forms 0.20 mol of MgO. Mass = 0.20 × 40 = 8.0 g.

Correct: (D)

The negative bromide ions move to the positive electrode, lose electrons and form bromine.

Correct: (B)

The cathode is the negative electrode, so it attracts the positively charged cations.

Correct: (D)

With copper electrodes, copper dissolves from the anode (Cu → Cu^2+ + 2e^-) and is deposited on the cathode, so the solution concentration stays the same.

Correct: (B)

Aluminium is a very reactive metal, above carbon in the reactivity series, so it is extracted by electrolysis of its molten oxide.

Correct: (C)

The voltage is largest when the two metals are furthest apart in the reactivity series; magnesium is much more reactive than copper.

Correct: (A)

Thermal decomposition takes in heat from the surroundings (the mixture must be kept heated), so it is endothermic.

Correct: (A)

Bonds broken: 945 + (3 × 436) = 2253 kJ. Bonds formed: 6 × 391 = 2346 kJ. Energy change = 2253 – 2346 = -93 kJ/mol.

Correct: (C)

Energy = 100 × 4.2 × 20 = 8400 J = 8.4 kJ.

Correct: (B)

In an exothermic reaction energy is released to the surroundings, so the products end up with less energy than the reactants.

Correct: (D)

In a hydrogen-oxygen fuel cell the product is water only, making it a clean source of electrical energy.

Correct: (B)

Powder has a much larger surface area than a lump, so collisions at the surface happen more frequently and the rate increases.

Correct: (D)

Plotting the volume of gas produced against time gives the rate; the steeper the gradient, the faster the reaction.

Correct: (A)

At higher temperature the particles move faster, colliding more often, and more of the collisions exceed the activation energy.

Correct: (C)

The Haber process uses about 450 °C and 200 atm with an iron catalyst, a compromise between rate and yield.

Correct: (D)

Copper(II) oxide loses oxygen (and the copper gains electrons, +2 to 0), so CuO is reduced; hydrogen is oxidised.

Correct: (A)

Oxidation Is Loss of electrons (OIL); reduction is gain of electrons.

Correct: (C)

Equilibrium is dynamic: both reactions continue at equal rates, so the overall amounts remain constant.

Correct: (B)

Acids turn blue litmus red and have a pH below 7. Feeling soapy and containing OH^- ions are properties of alkalis.

Correct: (B)

Calcium oxide is a metal oxide; it reacts with acids to form a salt and water, so it is basic. The others are acidic non-metal oxides.

Correct: (C)

Zinc sulfate is soluble, so it is made by reacting an insoluble solid (zinc carbonate) with the acid, filtering off the excess, and crystallising the solution.

Correct: (D)

Sodium chloride is made by titrating sodium hydroxide solution with hydrochloric acid, because both the alkali and the salt are soluble and colourless.

Correct: (A)

Nitrate ions are reduced by aluminium in alkaline solution to ammonia gas, which is alkaline and turns damp red litmus blue.

Correct: (A)

In every acid-alkali neutralisation, hydrogen ions from the acid react with hydroxide ions from the alkali to form water; the other ions are spectators.

Correct: (D)

An oxide that reacts with both acids and alkalis is called amphoteric; zinc oxide is another example.

Correct: (B)

Four shells means Period 4 and 2 outer electrons means Group II (the element is calcium).

Correct: (C)

Reactivity decreases down Group VII, so of the halogens listed, chlorine (the highest in the group) is the most reactive.

Correct: (C)

Transition elements form coloured compounds, have high melting points and variable oxidation states, unlike the Group I metals.

Correct: (B)

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

Correct: (A)

Magnesium reacts extremely slowly with cold water but reacts with steam to form magnesium oxide and hydrogen. Potassium and calcium react with cold water; copper does not react even with steam.

Correct: (D)

Stainless steel contains chromium (and often nickel), which gives the steel its resistance to rusting.

Correct: (D)

Zinc is in the middle of the reactivity series, so its oxide is reduced by heating with carbon (coke): ZnO + C → Zn + CO.

Correct: (A)

Rust is hydrated iron(III) oxide, Fe2O3.xH2O, formed when iron is exposed to oxygen and water.

Correct: (B)

Sulfur dioxide, released when fossil fuels containing sulfur burn, dissolves in rainwater to form acid rain.

Correct: (C)

Ammonium phosphate, (NH4)3PO4, contains nitrogen (from the ammonium ions) and phosphorus (from the phosphate ions).

Correct: (A)

A small amount of chlorine sterilises the water by killing harmful microorganisms; insoluble solids are removed earlier by filtration.

Correct: (C)

Alkanes are saturated hydrocarbons with general formula CnH2n+2, e.g. ethane is C2H6.

Correct: (D)

Saturated hydrocarbons have only single bonds and fit CnH2n+2: C4H10 (butane). The others fit CnH2n and are alkenes.

Correct: (B)

The hydration of ethene uses a phosphoric acid catalyst at about 300 °C and 60 atm pressure. Yeast is used for the fermentation method instead.

Correct: (B)

Carboxylic acids react with alcohols to form esters; here ethyl ethanoate and water are produced.

Correct: (D)

In addition polymerisation, the C=C bonds of many alkene monomers open up and join into a long chain, with no by-product.

Correct: (C)

Hydrogen burns explosively with a squeaky pop when a lighted splint is applied. (The splint test that relights is for oxygen, and limewater tests for carbon dioxide.)

Correct: (A)

The liquids are miscible but have different boiling points, so fractional distillation separates them; filtration only works for insoluble solids in liquids.