46 questions. Try each one, then open the answer to check yourself and read the explanation.
The movement of liquid molecules from the surface of the liquid to the gaseous phase above it is known as
Answer: C (evaporation)
Molecules with enough energy escape from the surface of a liquid into the gas above it; this is evaporation. Condensation is the reverse.
What mass of a divalent metal M (atomic mass = 40) would react with excess hydrochloric acid to liberate 224 cm3 of dry hydrogen gas measured at S.T.P? [G.M.V = 22.4 dm3]
Answer: D (0.4 g)
M + 2HCl → MCl2 + H2, so 1 mol of M gives 1 mol of H2. 224 cm3 is 0.01 mol of H2, so 0.01 × 40 = 0.4 g of M is needed.
10 cm3 of hydrogen fluoride gas reacts with 5 cm3 of dinitrogen difluoride gas (N2F2) to form 10 cm3 of a single gas. Which of the following is the most likely equation of the reaction?
Answer: B (2HF + N2F2 → 2NHF2)
By Gay-Lussac's law the volumes 10 : 5 : 10 give the mole ratio 2 : 1 : 2. Only 2HF + N2F2 → 2NHF2 has this ratio and is balanced.
The number of atoms of chlorine present in 5.85 g of NaCl is [Na = 23, Cl = 35.5] [Avogadro's Number = 6.02 × 1023].
Answer: A (6.02 × 1022)
Molar mass of NaCl = 58.5 g, so 5.85 g is 0.1 mol, containing 0.1 mol of chlorine. 0.1 × 6.02 × 1023 = 6.02 × 1022 atoms.
How much of magnesium is required to react with 250 cm3 of 0.5 M HCl? [Mg = 24]
Answer: B (1.5 g)
Moles of HCl = 0.25 × 0.5 = 0.125 mol. Mg + 2HCl → MgCl2 + H2, so Mg = 0.0625 mol × 24 = 1.5 g.
200 cm3 of oxygen diffuse through a porous plug in 50 seconds. How long will 80 cm3 of methane (CH4) take to diffuse through the same porous plug under the same conditions? [C = 12, O = 16, H = 1].
Answer: C (14 sec)
Oxygen's rate is 200/50 = 4 cm3/s. By Graham's law methane is √(32/16) = 1.414 times faster, about 5.66 cm3/s, so 80 cm3 takes 80/5.66 ≈ 14 s.
The relationship between the velocity (U) of gas molecules and their relative molecular mass (M) is shown by the equation
Answer: D (U = (k/m)½)
Graham's law says the speed of gas molecules is inversely proportional to the square root of the molar mass, so U = √(k/M) = (k/M)½.
An element with atomic number twelve is likely to be
Answer: B (electrovalent with a valency of 2)
Atomic number 12 is magnesium, 2,8,2. It loses its two outer electrons to form Mg2+ ions, so it forms electrovalent bonds with a valency of 2.
Which of the following groups of physical properties increases from left to right of the Periodic Table? 1 Ionization energy 2 Atomic radius 3 Electronegativity 4 Electron affinity
Answer: C (3 and 4)
Across a period the nuclear charge rises, so electronegativity and electron affinity increase while atomic radius decreases. Every option except C includes atomic radius, which does not increase.
When 50 cm3 of a saturated solution of sugar (molar mass 342.0 g) at 40°C was evaporated to dryness, 34.2 g of dry solid was obtained. The solubility of sugar at 40°C is
Answer: D (2.0 moles dm−3)
34.2 g is 0.1 mol of sugar in 50 cm3. In 1000 cm3 that is 0.1 × 20 = 2.0 mol, so the solubility is 2.0 mol dm−3.
Which of the following salts when dissolved in water will NOT give the corresponding pH value?
Answer: D (NaHCO3, pH < 6.)
Sodium hydrogencarbonate solution is mildly alkaline (pH about 8), so pH < 6 is wrong. NaHSO4 is acidic, Na2CO3 is alkaline and NaCl is neutral.
Which of the following is an acidic salt?
Answer: A (NaHSO4)
An acid salt still contains replaceable hydrogen from its parent acid. NaHSO4 has one of the two hydrogens of H2SO4 left.
Which of the following solutions will conduct the least amount of electricity?
Answer: D (0.01 M aqueous solution of sugar.)
Sugar is a non-electrolyte: it dissolves as molecules, not ions, so its solution hardly conducts at all.
In the electrolysis of aqueous solution of K2SO4 in the above cell, which species migrate to the anode?
Answer: A (SO42− and OH−)
The anode is positive, so the negative ions move to it. In K2SO4 solution these are SO42− and OH−.
How many coulombs of electricity are passed through a solution in which 6.5 amperes are allowed to run for 1.0 hour?
Answer: D (2.34 × 104 coulombs)
Quantity of electricity = current × time in seconds = 6.5 A × 3600 s = 23400 C, that is 2.34 × 104 coulombs.
Which of these represents a redox reaction?
Answer: D (Zn + 2HCl → ZnCl2 + H2)
In D zinc goes from 0 to +2 (oxidised) and hydrogen from +1 to 0 (reduced). In the other reactions no oxidation number changes.
How many electrons are transferred in reducing one atom of Mn in the reaction MnO2 + 4HCl → MnCl2 + 2H2O + Cl2?
Answer: A (2)
Manganese changes from +4 in MnO2 to +2 in MnCl2, so each Mn atom gains 2 electrons.
20 cm3 of 0.1 molar NH4OH solution when neutralized with 20.05cm3 of 0.1 molar HCl liberated 102 joules of heat. Calculate the heat of neutralization of NH4OH
Answer: A (−51.0 KJ mol−1)
Moles of NH4OH = 0.020 × 0.1 = 0.002 mol. 102 J / 0.002 = 51000 J = 51.0 kJ per mole, and since heat was given out, ΔH = −51.0 kJ mol−1.
What is the consequence of increasing pressure on the equilibrium reaction ZnO(s) + H2(g) ⇌ Zn(s) + H2O(l)?
Answer: B (The equilibrium is driven to the right)
Increasing pressure favours the side with fewer gas molecules. There is one mole of gas (H2) on the left and none on the right, so the equilibrium moves to the right.
The approximate volume of air containing 10 cm3 of oxygen is
Answer: C (50 cm3)
Air is about one-fifth (20%) oxygen, so 10 cm3 of oxygen is found in about 5 × 10 = 50 cm3 of air.
The reaction Mg + H2O → MgO + H2 takes place only in the presence of
Answer: D (steam)
Magnesium reacts only very slowly with cold water (giving the hydroxide). Heated magnesium burns in steam to give magnesium oxide and hydrogen.
When steam is passed through red hot carbon, which of the following are produced?
Answer: C (Hydrogen and carbon (II) oxide)
Steam over red-hot coke gives water gas: C + H2O → CO + H2, a mixture of carbon (II) oxide and hydrogen.
Which of the following contains an efflorescent, a deliquescent and a hygroscopic substance respectively?
Answer: C (Na2CO3.10H2O, FeCl3, concentrated H2SO4)
Washing soda (Na2CO3.10H2O) loses water to the air (efflorescent), FeCl3 absorbs water until it dissolves (deliquescent), and concentrated H2SO4 absorbs water without dissolving into a solution of a solid (hygroscopic).
The tabulated results below were obtained by titrating 10.0 cm3 of water with soap. The titration was repeated with the same sample of water after boiling.
Before boiling: Final (cm3) 25.0, Initial (cm3) 0.0
After boiling: Final (cm3) 20.0, Initial (cm3) 15.0
The ratio of permanent to temporary hardness is
Answer: B (1:4)
Boiling removes only temporary hardness, so the 5.0 cm3 titre after boiling measures permanent hardness. Temporary hardness = 25.0 − 5.0 = 20.0, giving permanent : temporary = 5 : 20 = 1 : 4.
The exhaust fumes from a garage in a place that uses petrol of high sulphur content are bound to contain
Answer: B (CO and SO2)
Incomplete burning of petrol in an engine gives carbon (II) oxide, and the sulphur impurity burns to sulphur (IV) oxide, SO2.
Oxygen-demanding wastes are considered to be a water pollutant because they
Answer: A (deplete oxygen which is necessary for the survival of aquatic organisms)
Bacteria breaking down these wastes use up the dissolved oxygen in the water, so fish and other aquatic life suffocate.
Which of the following will react further with oxygen to form a higher oxide?
Answer: C (SO2 and NO)
SO2 can be oxidised to SO3, and NO reacts with oxygen to give NO2. CO2 and H2O are already the highest oxides.
In the course of an experiment, two gases X and Y were produced. X turned wet lead ethanoate to black and Y bleached moist litmus paper. What are the element(s) in each of the gases X and Y respectively?
Answer: A (H and S;Cl)
X blackens lead ethanoate paper, so it is hydrogen sulphide (H and S). Y bleaches moist litmus, so it is chlorine (Cl).
Which of the following sulphides is insoluble in dilute HCl?
Answer: C (CuS)
Copper (II) sulphide is so insoluble that dilute acid does not dissolve it (it is precipitated from acid solution in group analysis). Na2S, ZnS and FeS dissolve, giving H2S.
When chlorine is passed into water and subsequently exposed to sunlight, the gas evolved is
Answer: C (O2)
Chlorine water contains HOCl, which breaks down in sunlight: 2HOCl → 2HCl + O2. The gas given off is oxygen.
Which of the following metals does NOT form a stable trioxocarbonate (IV)?
Answer: B (Al)
Iron (II), zinc and lead carbonates all exist. Aluminium carbonate is not stable: Al3+ in water gives Al(OH)3 and CO2 instead.
A substance Z reacts with NaOH to give salt and water only. When Z is treated with dilute HCl, a gas is evolved which gives a yellow suspension on passing into concentrated H2SO4. Substance Z is
Answer: A (NaHS)
Z reacts with NaOH, so it is an acid salt. With HCl it gives H2S, which concentrated H2SO4 oxidises to yellow sulphur, so Z is NaHS.
Ammonia gas is normally dried with
Answer: B (quicklime)
Ammonia is alkaline, so it reacts with the acid drying agent H2SO4, and it also combines with CaCl2. Quicklime (CaO), a basic drying agent, is used.
What are the values of x, y and z respectively in the equation: xCu + yHNO3 → xCu(NO3)2 + 4H2O + zNO?
Answer: B (3:8:2)
The balanced equation is 3Cu + 8HNO3 → 3Cu(NO3)2 + 4H2O + 2NO; check: 8 H on each side and 8 N on each side. So x = 3, y = 8, z = 2.
The Iron (III) oxide impurity in bauxite can be removed by
Answer: B (dissolution in sodium hydroxide and filtration)
Aluminium oxide is amphoteric and dissolves in hot NaOH, but iron (III) oxide does not. The iron oxide is then filtered off.
Which of the following does NOT contain aluminium as a component?
Answer: C (Container for caustic soda)
Aluminium reacts with sodium hydroxide solution, so it cannot hold caustic soda. It is used for overhead cables, in the alloy duralumin and for nitric acid containers.
A white solid suspected to be lead trioxonitrate (V), zinc trioxocarbonate (IV) or calcium trioxocarbonate (IV) was heated strongly. Its residue which was yellow when hot and white when cold is
Answer: C (zinc oxide)
Zinc oxide is the residue that is yellow when hot and white when cold. Lead (II) oxide is reddish-brown hot and yellow cold, and calcium oxide stays white.
Which of the following compounds would give lilac flame coloration and a white precipitate with acidified barium chloride solution?
Answer: C (K2SO4)
A lilac flame shows potassium, and a white precipitate with acidified BaCl2 shows sulphate. So the compound is K2SO4.
How will a metal X, which reacts explosively with air and with dilute acids be best extracted from its ores?
Answer: D (Electrolysis of fused salt.)
Such a very reactive metal would react with water, so it can't be got from solution. It is extracted by electrolysing its molten (fused) salt.
Which of the following is NOT a correct test for the named organic compound in each case?
Answer: B (Glucose when reacted with Na2CrO4 at 0°C will show immediate discharge of colour)
Glucose is not tested this way: it does not instantly discharge the colour of a chromate at 0°C (it is tested with Fehling's or Benedict's solution). The other three are correct tests.
Which of the following is used as an 'anti-knock' in automobile engines?
Answer: B (Lead tetra-ethyl)
Tetraethyl lead was added to petrol to stop knocking (early ignition). n-Heptane knocks badly and is the zero of the octane scale.
What reaction takes place when palm-oil is added to potash and foams are observed?
Answer: B (Saponification)
The oil (an ester) is hydrolysed by the alkali (potash) to form soap, which foams. This is saponification.
Which is the structural formula for pent-2-enoic acid?
Answer: C (Structure C)
Pent-2-enoic acid is CH3CH2CH=CHCOOH: five carbons, a –COOH group, and a C=C between carbons 2 and 3 counting from the COOH carbon. Structure C shows this; B ends in a ketone group, not –COOH, and D has no double bond.
When ethanol is heated with excess concentrated sulphuric acid, the ethanol is
Answer: C (dehydrated to ethene)
Hot excess concentrated H2SO4 removes a molecule of water from ethanol: C2H5OH → C2H4 + H2O. This is dehydration to ethene.
Which of the following compounds is NOT formed by the action of chlorine on methane?
Answer: B (C2H5Cl)
Chlorine replaces the hydrogens of methane one at a time, giving CH3Cl, CH2Cl2, CHCl3 and CCl4. These all have one carbon, so C2H5Cl is not formed.
Which of the following are made by the process of polymerization?
Answer: B (Nylon and artificial rubber)
Nylon and synthetic rubber are polymers made by joining many small monomer molecules. Soap comes from saponification and margarine from hydrogenation.