47 questions. Try each one, then open the answer to check yourself and read the explanation.
Which of the following equimolar solutions will have the highest pH?
Answer: B (NaOH)
NaOH is a strong alkali and ionises completely, so it gives the most OH− ions and the highest pH. NH4OH is a weak base and CH3COONa only slightly alkaline by hydrolysis.
Which of the following ions requires the largest quantity of electricity for discharge at an electrode?
Answer: D (2.0 moles of Al3+)
Faradays needed = moles × charge: Cl− 4 × 1 = 4F, Na+ 3 × 1 = 3F, Cu2+ 2.5 × 2 = 5F, Al3+ 2 × 3 = 6F. Al3+ needs the most.
Phenolphthalein in acidic solution is
Answer: C (colourless)
Phenolphthalein is colourless in acidic and neutral solutions and turns pink in alkaline solutions.
When iron is exposed to moisture and it rusts, the value of ΔG for the reaction is
Answer: D (negative)
A reaction that takes place spontaneously has a negative free-energy change (ΔG below zero). Iron rusts by itself in moist air, so ΔG is negative.
2H2 + O2 → 2H2O ΔH = −571 kJ
In the equation above, how much heat will be liberated if 12.0g of hydrogen is burnt in excess oxygen?
Answer: D (−1713 kJ)
2 mol H2 = 4.0 g releases 571 kJ. 12.0 g is three times that, so ΔH = 3 × (−571) = −1713 kJ.
A concentrated solution containing H+, Cu2+, OH− and Cl− was electrolyzed using platinum electrodes. The ion that will be discharged at the cathode is
Answer: A (Cu2+)
Cations go to the cathode. Cu2+ is lower than H+ in the electrochemical series, so it is discharged first as copper metal.
When sulphur (IV) oxide is passed into a solution of sodium hydroxide for a long time, it eventually produces a solution of
Answer: C (NaHSO3)
SO2 first forms Na2SO3; with excess SO2 this reacts further (Na2SO3 + SO2 + H2O → 2NaHSO3) to give sodium hydrogensulphite.
What is the correct IUPAC name for NO2−?
Answer: D (Dioxonitrate (III) ion)
NO2− has two oxygens (dioxo) and nitrogen is +3 (x − 4 = −1), so it is dioxonitrate(III) ion.
What will happen if an aluminium spoon is used to stir a solution of iron (II) trioxonitrate (V)?
Answer: A (The spoon will be oxidized while the iron (II) ions will be reduced to the metal.)
Aluminium is more reactive than iron, so it displaces iron: Al loses electrons (is oxidised) and Fe2+ gains electrons to form iron metal (is reduced).
CH3 − CH(CH3) − CH = CH2
The IUPAC nomenclature for the hydrocarbon above is
Answer: D (3-methylbut-1-ene)
The longest chain has 4 carbons (butene). Numbering from the end nearest the double bond puts it at C1 and the methyl group on C3: 3-methylbut-1-ene.
The enzyme responsible for converting sucrose into two simple isomeric sugars is
Answer: C (invertase)
Invertase (sucrase) hydrolyses sucrose into glucose and fructose, which are isomers (both C6H12O6).
The decolourization of the purple colour of tetraoxomanganate (VII) ion is a test for
Answer: A (alkenes)
Alkenes have a C=C double bond which is oxidised by acidified KMnO4, so the purple colour disappears; this is the standard test for unsaturation.
Which of the following are structural isomers?
Answer: B (Propanal and propanone)
Propanal (CH3CH2CHO) and propanone (CH3COCH3) both have the formula C3H6O but different structures.
In the purification of impure samples of ethyl ethanoate synthesized by esterification, concentrated sodium trioxocarbonate (IV) solution is used to remove
Answer: C (acidic impurities)
Na2CO3 is basic, so it neutralises leftover ethanoic acid and the acid catalyst, removing acidic impurities.
How many hydrogen atoms does a single ring cycloalkane have less than the corresponding open-chain alkane?
Answer: A (Two)
Alkanes are CnH2n+2 and cycloalkanes are CnH2n; closing the ring removes two hydrogen atoms.
Equal moles of ethyne and hydrogen iodide react to give
Answer: D (CH2 = CHI)
One mole of HI adds across one of the two π bonds of the triple bond: HC≡CH + HI → CH2=CHI (iodoethene).
A substance that is used as a ripening agent for fruits is
Answer: A (ethene)
Ethene is a plant hormone that speeds up the ripening of fruits.
When water boilers are used for a long period of time, the solid substances left behind as scale are
Answer: B (magnesium trioxosilicate (IV) and calcium tetraoxosulphate (VI))
Boiler scale forms from permanently hard water; the deposits are mainly calcium tetraoxosulphate(VI) and magnesium trioxosilicate(IV).
25cm3 of a mixture of noble gases was obtained from air after the removal of other constituents. What was the original volume of air?
Answer: A (2 500 cm3)
Noble gases make up about 1% of air, so the air volume = 25 × 100 = 2500 cm3.
The solubility curve shows the variation of solute concentration with
Answer: B (temperature)
A solubility curve plots how much solute dissolves (solubility) against temperature.
Kerosine is commonly used to remove the red colour stain of palm oil from clothes because it
Answer: C (makes the oil evaporate easily by dissolving it)
Palm oil is non-polar and dissolves in kerosene (a non-polar solvent); the volatile solvent then evaporates and carries the stain away.
The gas that is the most dangerous pollutant to humans is
Answer: D (hydrogen sulphide)
Hydrogen sulphide is extremely poisonous, even more toxic than carbon(II) oxide; small concentrations can paralyse breathing.
Natural water collected from rivers and ponds contains oxygen, carbon (IV) oxide and
Answer: A (nitrogen)
Rain and surface water dissolve gases from the air, so natural water contains dissolved nitrogen as well as oxygen and carbon(IV) oxide.
How many moles of limestone will be required to produce 5.6g of CaO? [Ca=40, C=12, O=16]
Answer: B (0.10 mol)
CaCO3 → CaO + CO2 (1 : 1). Moles of CaO = 5.6/56 = 0.10 mol, so 0.10 mol of limestone is needed.
The shape of the hydrocarbon compound CH4 is
Answer: D (tetrahedral)
Carbon in methane is sp3 hybridised; its four bonds point to the corners of a tetrahedron (109.5°).
Which of these properties gives a solid its definite shape?
Answer: A (Strong intermolecular attraction)
In a solid, strong attractive forces hold the particles in fixed positions, so the solid keeps its shape.
Sugar is separated from its impurities by
Answer: B (crystallization)
Sugar decomposes on strong heating, so it is purified by crystallisation: pure crystals form as a saturated solution cools, leaving impurities in solution.
The component of an atom that contributes least to its mass is the
Answer: D (electron)
Protons and neutrons each have a mass of about 1 a.m.u., while an electron's mass is only about 1/1840 a.m.u., so electrons add almost nothing to an atom's mass.
An element will readily form an electrovalent compound if its electron configuration is
Answer: A (2, 8, 1)
An atom with 2, 8, 1 (sodium) easily loses its single outer electron to form Na+, so it readily forms ionic (electrovalent) compounds.
A heterogenous mixture can be defined as any mixture
Answer: C (whose composition is not uniform)
A heterogeneous mixture does not have the same composition throughout; its parts can be seen or separated.
The pressure of 100cm3 of oxygen at 35°C is 750mmHg. What will be the volume of the gas if the pressure is reduced to 100mmHg without changing the temperature?
Answer: D (750 cm3)
At constant temperature, Boyle's law: P1V1 = P2V2, so V2 = 750 × 100 / 100 = 750 cm3.
I. Treatment of cancer
II. Detection of leakages in water mains
III. Detection of the ages of ancient tools
IV. Preparation of drugs
Which combination of the above refers to the uses of radioactive isotopes?
Answer: C (I, II and III)
Radioisotopes are used in radiotherapy for cancer, as tracers to find leaks, and in carbon dating of old objects; they are not used to prepare drugs.
What is the valence shell electron configuration of the element with atomic number 17?
Answer: D (3s23p5)
Element 17 (chlorine) is 1s22s22p63s23p5; its valence shell is the third shell, 3s23p5 (7 electrons).
The density of a certain gas is 1.98gdm−3 at s.t.p. What is the molecular mass of the gas? [Molar volume of a gas at s.t.p. = 22.4 dm3]
Answer: A (44.0 g)
Molar mass = density × molar volume = 1.98 × 22.4 ≈ 44 g.
When pure aluminium metal is heated to red hot in the presence of nitrogen gas, the compound formed is
Answer: C (AlN)
Aluminium is +3 and nitride is N3−, so they combine 1 : 1 to give aluminium nitride, AlN.
A dense white fume is formed when ammonia gas reacts with
Answer: D (HCl(g))
NH3 + HCl → NH4Cl; the solid ammonium chloride particles appear as dense white fumes.
N2(g) + 3H2(g) ⇌ 2NH3(g) ΔH = −90 kJ
In the equation above, the yield of ammonia can be decreased by
Answer: C (increasing the temperature)
The forward reaction is exothermic, so raising the temperature shifts the equilibrium to the left and less ammonia is formed.
The gas that can be dried using concentrated tetraoxosulphate (VI) acid is
Answer: B (sulphur (IV) oxide)
Concentrated H2SO4 reacts with ammonia (a base) and oxidises HBr and H2S, but does not react with acidic SO2, so it can dry SO2.
NH4Cl(s) ⇌ NH3(g) + HCl(g)
The reaction above can only attain equilibrium if
Answer: C (it is in a closed system)
Equilibrium needs both forward and reverse reactions; in an open system the gaseous products escape, so it can only be reached in a closed system.
The most suitable metal that can be used as a lightning conductor is
Answer: B (copper)
Copper is an excellent electrical conductor, resists corrosion and is much cheaper than silver, so it is used for lightning conductors.
In the diagram above (a graph of ln k against 1/T showing lines X, Y, Z and R), which of the curves illustrates Arrhenius' law?
Answer: D (X)
Arrhenius: ln k = ln A − Ea/(RT). A plot of ln k against 1/T is a straight line with a negative slope, which is line X.
The most abundant element on the earth's crust is
Answer: C (oxygen)
Oxygen makes up nearly half of the earth's crust by mass, mostly combined in silicates and oxides.
Metalloids are also referred to as
Answer: A (semi-metals)
Metalloids such as silicon have properties between metals and non-metals, so they are called semi-metals.
The ores that can be concentrated by flotation are
Answer: B (sulphide ores)
In froth flotation, sulphide ore particles stick to oil froth and float while the earthy impurities sink.
In a flame test for calcium, the flame appears
Answer: A (green when viewed through a blue glass)
Calcium colours a flame brick-red. Blue cobalt glass absorbs much of the red-orange light, so the calcium flame looks (light) green through it.
Which of the following alloys contain iron?
Answer: C (Steel and permalloy)
Steel is iron with carbon, and permalloy is a nickel–iron alloy. Duralumin, brass, bronze and solder contain no iron.
To obtain pure carbon (II) oxide from its mixture with carbon (IV) oxide, the mixture should be
Answer: D (bubbled through sodium hydroxide)
Sodium hydroxide absorbs the acidic CO2 (forming Na2CO3) while the neutral CO passes through unchanged.