45 questions. Try each one, then open the answer to check yourself and read the explanation.
Sodium chloride may be obtained from brine by
Answer: D (evaporation)
Brine is a solution of sodium chloride in water. Evaporating the water leaves the solid salt behind.
20 cm3 of hydrogen gas are sparked with 20 cm3 of oxygen gas in an endiometer at 373 K (100°C) and 1 atmosphere. The resulting mixture is cooled to 298 K (25°C) and passed over calcium chloride. The volume of the residual gas is
Answer: D (10 cm3)
2H2 + O2 → 2H2O, so 20 cm3 of hydrogen uses only 10 cm3 of oxygen. The water is condensed and absorbed by calcium chloride, leaving 10 cm3 of unused oxygen.
Manganese (IV) oxide reacts with concentrated hydrochloric acid according to the equation MnO2 + xHCl → MnCl2 + Cl2 + yH2O. x and y are
Answer: D (4 and 2 respectively)
There are 4 Cl atoms on the right (2 in MnCl2, 2 in Cl2), so x = 4. The 2 O atoms from MnO2 (and the 4 H atoms) make 2H2O, so y = 2.
Which among the elements 1. Carbon 2. Oxygen 3. Copper 4. Bromine 5. Zinc, will NOT react with either water or steam?
Answer: B (2 and 3)
Red-hot carbon reacts with steam (water gas), zinc reacts with steam, and bromine reacts slightly with water. Oxygen and copper do not react with water or steam.
Which of the curves shown in Fig. 1 represents the relationships between the volume (v) and pressure (p) of an ideal gas at constant temperature?
Answer: C (3)
Boyle's law says V = k/p at constant temperature, so a graph of V against 1/p is a straight line rising steadily. Curve 3 is that straight line.
Naphthalene when heated melts at 354 K (81°C). At this temperature the molecules of naphthalene
Answer: E (become mobile as the inter molecular forces are broken.)
Melting is a physical change: heat overcomes the forces holding the molecules in the solid, so the molecules become free to move about as a liquid.
The ratio of the number of molecules in 2 g of hydrogen to that in 16 g of oxygen is
Answer: A (2:1)
2 g of H2 is 1 mole and 16 g of O2 is 0.5 mole. Equal moles mean equal numbers of molecules, so the ratio is 1 : 0.5 = 2 : 1.
Which combination of the following statements is correct?
1. lowering the activation energy
2. conducting the reaction in a gaseous state
3. increasing the temperature
4. removing the products as soon as they are formed
5. powdering the reactant if solid
Answer: B (1, 3 and 5)
The rate of a reaction is increased by lowering the activation energy (a catalyst), raising the temperature and increasing the surface area of a solid by powdering it. Removing products changes the yield at equilibrium, not the rate.
Which of the following mixtures would result in a solution of pH greater than 7?
Answer: A (25.00 cm3 of 0.05 M H2SO4 and 25.00 cm3 of 0.50 M Na2CO3)
In A there are only 1.25 mmol of H2SO4 but 12.5 mmol of Na2CO3, so excess carbonate makes the solution alkaline. In C, D and E the acid is in excess, and in B the acid and hydrogencarbonate just neutralise each other.
In which of the following reactions does hydrogen peroxide act as a reducing agent?
Answer: D (PbO2 + 2HNO3 + H2O2 → Pb(NO3)2 + 2H2O + O2)
A reducing agent is itself oxidised. In D, H2O2 is oxidised to O2 while PbO2 (lead +4) is reduced to Pb(NO3)2 (lead +2). In the others H2O2 is reduced to water, so it is the oxidising agent.
For the reaction 2Fe3+ + 2I− → 2Fe2+ + I2, which of the following statements is TRUE?
Answer: C (I− is oxidized to I2)
Each I− loses an electron to become iodine, so iodide is oxidised. Fe3+ gains those electrons and is reduced to Fe2+.
The diagram above (Fig. 3) shows the energy profile for the reaction A + B = C + D. From this diagram, it is clear that the reaction is
Answer: D (exothermic)
The products end at a lower energy (about 42 kJ) than the reactants (about 60 kJ). Energy is given out, so the reaction is exothermic.
In dilute solution the heat of the reaction NaOH + HCl = NaCl + H2O is −57.3 kJ. Therefore the heat of the reaction 2NaOH + H2SO4 → Na2SO4 + 2H2O is
Answer: D (−114.6 kJ)
−57.3 kJ is released for each mole of water formed in neutralisation. This reaction forms 2 moles of water, so the heat is 2 × (−57.3) = −114.6 kJ.
For the reactions: (I) Melon oil + NaOH ⇌ Soap + Glycerol (II) 3Fe + 4H2O ⇌ Fe3O4 + 4H2 (III) N2O4 ⇌ 2NO2, which of the following satements is true?
Answer: B (All the reactions demonstrate Le Chatelier's principle.)
All three are reversible reactions at equilibrium, so each responds to changes as Le Chatelier's principle predicts. A catalyst never changes the yield, and higher pressure would lower the yield in III, which makes more gas molecules.
Which of the following methods may be used to prepare trioxonitrate (V) acid (nitric acid) in the laboratory?
Answer: C (Heating sodium trioxonitrate (V) with tetraoxosulphate (VI) acid)
In the laboratory, a trioxonitrate (V) salt such as NaNO3 or KNO3 is heated with concentrated H2SO4; the more volatile nitric acid distils off.
Lime-water, which is used in the laboratory for the detection of carbon (IV) oxide, is an aqueous solution of
Answer: A (Ca(OH)2)
Lime-water is a solution of calcium hydroxide. CO2 turns it milky by forming insoluble calcium carbonate.
An element that can exist in two or more different structural forms which possess the same chemical properties is said to exhibit
Answer: E (allotrophy)
Different structural forms of the same element in the same physical state, such as diamond and graphite, are allotropes; the property is allotropy.
Sulphur
Answer: C (burns with a blue flame)
Sulphur burns in air with a blue flame to form sulphur (IV) oxide. Its oxides are acidic, it does not conduct, and it is white phosphorus, not sulphur, that is kept under water.
Which of the following statements is NOT true of carbon monoxide?
Answer: B (CO is readily oxidized at room temperature by air to form CO2)
Carbon monoxide only burns to CO2 when it is ignited; it is not readily oxidised by air at room temperature. The other statements are true.
From the reactions. ZnO + Na2O → Na2ZnO2 and ZnO + CO2 → ZnCO3 it may be concluded that zinc oxide is
Answer: D (amphoteric)
ZnO reacts with the basic oxide Na2O (acting as an acid) and with the acidic oxide CO2 (acting as a base). An oxide that does both is amphoteric.
An example of a neutral oxide is
Answer: D (CO)
Carbon monoxide reacts with neither acids nor alkalis, so it is neutral. Al2O3 is amphoteric; NO2, CO2 and SO2 are acidic.
3Cl2 + 2NH3 → N2 + 6HCl. In the above reaction, ammonia acts as
Answer: A (a reducing agent)
Nitrogen goes from −3 in NH3 to 0 in N2, so ammonia is oxidised. It gives electrons to chlorine, so it is the reducing agent.
In the Haber process for the manufacture of ammonia, finely divided iron is used as
Answer: C (a catalyst)
Finely divided iron speeds up the reaction of nitrogen with hydrogen without being used up, so it is a catalyst.
An organic compound with a vapour density 56.5 has the following percentage composition: C = 53.1%, N = 12.4%, O = 28.3%, H = 6.2%. The molecular formula of the compound is (Relative atomic masses: N = 14, O = 16, C = 12, H = 1)
Answer: D (C5H7O2N)
Moles: C 53.1/12 = 4.43, N 12.4/14 = 0.886, O 28.3/16 = 1.77, H 6.2/1 = 6.2; dividing by 0.886 gives C5H7O2N (mass 113). Relative molecular mass = 2 × 56.5 = 113, so the molecular formula is C5H7O2N.
The hybridization of the carbon atom in ethyne is
Answer: D (sp)
Each carbon in ethyne (H–C≡C–H) forms a triple bond and is joined to only two atoms in a straight line, which needs sp hybridisation.
When the kerosene fraction from petrol is heated at high temperature, a lower boiling liquid is obtained. This process is known as
Answer: D (cracking)
Breaking large hydrocarbon molecules into smaller, lower-boiling ones by heat is called cracking.
The name of the compound CH3—CH2—COOH (shown) is
Answer: E (propanoic acid.)
The compound has three carbon atoms and a –COOH group, so it is propanoic acid.
Alkaline hydrolysis of naturally occurring fats and oils yields
Answer: B (soaps and glycerol)
Boiling fats or oils with an alkali (saponification) splits the esters into soap (the sodium salt of the fatty acid) and glycerol.
Which of the following represents a carboxylic acid?
Answer: A (R—C(OH)=O)
A carboxylic acid contains the –COOH group: a carbon with a C=O and an –OH. B is an ester and E is an aldehyde.
Which of the following statements is INCORRECT?
Answer: E (Calcium carbide will react with water to form any alkyne)
Calcium carbide and water give only one alkyne, ethyne (CaC2 + 2H2O → C2H2 + Ca(OH)2). The other statements are true.
Which of the following statements is NOT correct about all four of the acids: HBr, HNO3, H2CO3 and H2SO4? They
Answer: A (dissolve marble to liberate CO2)
Carbonic acid is too weak to release CO2 from marble, and H2SO4 soon stops reacting because insoluble CaSO4 coats the marble. So A is not true of all four.
If the cost of electricity required to deposit 1 g of magnesium is N5.00, how much would it cost to deposit 10g of aluminium? (Relative atomic masses: Al = 27, Mg = 24)
Answer: D (N66.67)
1 g of Mg (Mg2+) needs 2/24 = 0.0833 F. 10 g of Al (Al3+) needs 3 × 10/27 = 1.111 F, which is 13.33 times as much, so the cost is 13.33 × N5.00 = N66.67.
31R 199U 2412S 2010T 179Y. Which of the following statements is NOT true of the elements R, U, S, T, Y?
Answer: C (R, U, S and T are metals)
R (atomic number 1) is hydrogen, U and Y (atomic number 9) are fluorine and T (10) is neon, none of which is a metal. Only S (12, magnesium) is a metal, so C is false.
Nitrogen can best be obtained from a mixture of oxygen and nitrogen by passing the mixture over
Answer: D (heated phosphorus)
Heated phosphorus combines with the oxygen and removes it, leaving nitrogen. Heated magnesium would also react with the nitrogen, and gold, KOH and CaCl2 do not remove oxygen.
Water is said to be 'hard' if it
Answer: C (forms an insoluble scum with soap)
Hard water contains dissolved calcium and magnesium ions, which react with soap to form an insoluble scum instead of a lather.
Sodium hydroxide (NaOH) pellets are
Answer: A (deliquescent)
NaOH pellets absorb so much water from the air that they dissolve in it and form a solution, which is what deliquescent means.
Which of the following structural formulae is NOT isomeric with the others?
Answer: D (CH3–CH–CH–CH3 with an O bridging the two middle carbons)
A, B, C and E all have the formula C4H10O. D has the oxygen in a ring between two carbons, so it has only 8 hydrogens (C4H8O) and is not an isomer of the others.
Alkanes
Answer: C (contain only carbon and hydrogen)
Alkanes are hydrocarbons, made of carbon and hydrogen only, with the general formula CnH2n+2. They are insoluble in water and fairly unreactive.
If an excess of a liquid hydrocarbon is poured into a jar of chlorine, and the sealed jar is then exposed for several hours to bright sunlight, all the chlorine gas is consumed. The hydrocarbon is said to have undergone
Answer: D (a substitution reaction)
A saturated hydrocarbon reacts with chlorine only in sunlight, and chlorine atoms replace hydrogen atoms one by one. That is a substitution reaction.
The function of conc. H2SO4 in the esterification of ethanoic acid with ethanol is to
Answer: C (act as a catalyst)
A few drops of concentrated H2SO4 provide H+ ions that speed up the reaction between the acid and the alcohol, so it acts as a catalyst.
A piece of sea shell, when dropped into a dilute solution of hydrochloric acid, produces a colourless, odourless gas which turns clear limewater milky. The sea shell contains
Answer: C (calcium carbonate)
The gas that turns limewater milky is CO2, which comes from a carbonate reacting with acid. Sea shells are made of calcium carbonate.
Which of the following electrodes is used in electrolysis of bauxite (Al2O3) in molten cryolite?
Answer: B (Carbon electrodes)
In aluminium extraction both the anode (carbon blocks) and the cathode (the carbon lining of the cell) are carbon.
An aqueous solution of a metal salt, M, gives a white precipitate with NaOH which dissolves in excess NaOH. With aqueous ammonia, the solution of M also gives a white precipitate which dissolves in excess ammonia. Therefore the cation in M is
Answer: A (Zn2+)
Zn(OH)2 is white and dissolves in excess of both NaOH and ammonia. Al(OH)3 and Pb(OH)2 do not dissolve in excess ammonia, and copper gives a blue precipitate.
The I.U.P.A.C name for the compound CH3—CH(CH3)—CH2—CH3 is
Answer: D (2-methylbutane)
The longest chain has four carbons (butane) with a methyl group on carbon 2 when numbered from the nearer end, so the name is 2-methylbutane.
At S.T.P. how many litres of hydrogen can be obtained from the reaction of 500 cm3 of 0.5 M H2SO4 with excess zinc metal? (Gram molecular volume of H2 = 22.4 dm3).
Answer: D (5.6 dm3)
Moles of acid = 0.5 × 0.5 = 0.25 mol, and Zn + H2SO4 → ZnSO4 + H2 gives 0.25 mol of H2. Volume = 0.25 × 22.4 = 5.6 dm3.