44 questions. Try each one, then open the answer to check yourself and read the explanation.
The raw material used for the smelting of iron ore in a furnace is
Answer: B (CaCO3)
Limestone (CaCO3) is charged into the blast furnace with the ore and coke; it decomposes to CaO, which removes silica impurities as slag.
In the diagram above, gas X is
Answer: C (oxygen)
In sunlight chlorine water decomposes: 2HOCl → 2HCl + O2, so the gas collected is oxygen.
On heating, which of the following compounds will decompose to the free metal, nitrogen (IV) oxide and oxygen?
Answer: C (AgNO3)
Nitrates of metals low in the activity series, like silver, decompose right down to the metal: 2AgNO3 → 2Ag + 2NO2 + O2.
Group IA metals are not found free in nature because they
Answer: A (are very reactive and unstable)
Alkali metals lose their single outer electron very easily, so they react quickly with air and water and are always found combined in compounds.
In the diagram above, mixture Y is
Answer: D (NH4Cl(s) + Ca(OH)2(s))
Ammonia is prepared in the laboratory by heating an ammonium salt with a base: 2NH4Cl + Ca(OH)2 → CaCl2 + 2H2O + 2NH3, and dried with quicklime.
Carbon exists naturally in the combined state as
Answer: D (wood)
Graphite and diamond are free (uncombined) carbon and coal is largely impure free carbon, while in wood carbon is combined with hydrogen and oxygen in compounds such as cellulose.
The efficiency of a solid catalyst to increase reaction rates depends on its
Answer: A (surface area)
Reactions on a solid catalyst happen at its surface, so the larger the surface area (e.g. powder or fine mesh), the better it works.
Dynamic equilibrium describes a situation where
Answer: C (both forward and reverse reactions proceed at the same rate)
At dynamic equilibrium both reactions are still going on, but at equal rates, so concentrations stay constant (not necessarily equal).
The characteristic colour of the flame shown when a copper salt moistened with concentrated hydrochloric acid on a platinum wire is put on bunsen burner is
Answer: B (green)
Copper compounds give a green (bluish-green) flame. Lilac is potassium, yellow is sodium and brick-red is calcium.
The sulphide which is insoluble in dilute hydrochloric acid is
Answer: B (CuS)
CuS is extremely insoluble, so it does not dissolve in dilute HCl. FeS and ZnS dissolve in dilute acid giving H2S, and Na2S is soluble even in water.
Which of the following typically represents a photochemical reaction?
Answer: D (Conversion of silver halides to grey metallic silver.)
A photochemical reaction is started by light. Silver halides decompose in light to silver (the basis of photography).
The gas obtained as a product of anaerobic action on organic matter buried in the earth is
Answer: B (methane)
Bacteria decaying organic matter without air produce methane (marsh gas or natural gas).
2-methylbut-2-ene has the structure
Answer: D (CH3 — CH = C(CH3) — CH3)
But-2-ene has a 4-carbon chain with C=C between C2 and C3; a methyl group on C2 gives CH3−C(CH3)=CH−CH3, which is option D read from the other end.
CH3 — CH2 — C(CH3)(OH) — H
The oxidation of the compound above produces
Answer: A (2 – butanone)
The compound is butan-2-ol, a secondary alkanol. Secondary alkanols are oxidised to ketones, here butan-2-one (2-butanone).
Nigerian crude oil is described as light crude because of its
Answer: A (low sulphur content)
Nigerian crude is a light, sweet crude: it contains very little sulphur, which is the property the question's key relies on.
An example of aliphatic unsaturated hydrocarbon is
Answer: C (propene)
Propene is an open-chain (aliphatic) hydrocarbon with a C=C double bond. Pentane is saturated, butanol is not a hydrocarbon, and benzene is aromatic.
Which of the following functional groups will give gas bubbles when treated with a saturated solution of sodium hydrogen trioxocarbonate(IV)?
Answer: B (—COOH (—C(=O)—OH))
Carboxylic acids are strong enough to react with NaHCO3, releasing bubbles of CO2. Amines, alcohols and carbonyl compounds do not.
CH3 — CH2 — C ≡ CH
The hybridization in the compound above is
Answer: D (sp3 and sp)
The two saturated carbons (CH3 and CH2) are sp3; the two triple-bonded carbons are sp.
One mole of a hydrocarbon contains 36g of carbon and its vapour density is 20. The structure of the hydrocarbon is
Answer: A (CH3C≡CH)
Molar mass = 2 × 20 = 40 g. 36 g C = 3 mol C, leaving 4 g = 4 H, so the formula is C3H4, propyne CH3C≡CH.
An emulsion may be produced by shaking a detergent solution with
Answer: C (palm oil)
An emulsion is a liquid dispersed in another liquid it does not mix with. The detergent breaks palm oil into tiny droplets spread through the water.
The products of the combustion of candle wax are
Answer: C (carbon (IV) oxide and water)
Candle wax is a hydrocarbon; burning it completely in air gives carbon(IV) oxide and water.
Which of the following results in the fall of acid rain?
Answer: C (Oxides of sulphur)
Sulphur oxides dissolve in rain water to form sulphurous and sulphuric acids, causing acid rain.
Water has the ability to dissolve almost all substances because its molecule has a structure with
Answer: B (one positive end and one negative end)
Water is a polar molecule: the oxygen end is partly negative and the hydrogen end partly positive, so it attracts and surrounds ions and polar molecules.
When a crystal was added to the clear solution of its salt, the crystal did not dissolve and the solution remained unchanged. This showed that the solution was
Answer: D (saturated)
A saturated solution can hold no more solute at that temperature, so an added crystal neither dissolves nor grows. (In a supersaturated solution more crystals would form.)
A particle that contains 11 protons, 12 neutrons and 10 electrons is probably a
Answer: B (metallic ion)
11 protons is sodium; having one electron fewer than protons means it is the positive ion Na+, a metallic ion.
A difference between chemical and physical change is that in a chemical change
Answer: D (a new substance is formed)
A chemical change always produces a new substance; a physical change only alters the state or form.
The volume of 2.5 moles of oxygen at s.t.p. is [Molar volume of a gas at s.t.p. = 22.4 dm3]
Answer: D (56.0 dm3)
Volume = moles × molar volume = 2.5 × 22.4 = 56.0 dm3.
Nuclear fission involves the splitting of a heavy element into two nuclei of
Answer: A (nearly equal masses with a release of energy and radiation.)
In fission a heavy nucleus such as U-235 splits into two lighter nuclei of roughly similar size, releasing a lot of energy, neutrons and radiation.
What is the molar mass of a substance, if 0.4 mole of the substance has a mass of 25.0 g?
Answer: A (62.5 g)
Molar mass = mass ÷ moles = 25.0 ÷ 0.4 = 62.5 g.
The element with the electron configuration 1s22s2 2p3 is
Answer: D (nitrogen)
Adding up the electrons gives 2 + 2 + 3 = 7, the atomic number of nitrogen.
A decrease in atomic size and an increase in nuclear charge across a period lead to
Answer: C (a decrease in electropositivity)
Across a period the outer electrons are pulled more strongly by the nucleus, so atoms lose electrons less easily: elements become less electropositive (less metallic).
The order in which a mixture of sand, ammonium chloride and sodium chloride can be separated is
Answer: C (sublimation → dissolution → filtration → evaporation)
Heat first to sublime off NH4Cl; dissolve the rest in water; filter off the sand; then evaporate the filtrate to get NaCl.
The idea of planetary electrons was that of
Answer: A (Rutherford)
Rutherford's nuclear (planetary) model pictured electrons moving round a small dense nucleus like planets round the sun.
If 30 cm3 of a gas at 50°C is warmed to 80°C at a fixed pressure, the fractional increase in volume is
Answer: B (0.093)
Charles' law: V2 = 30 × 353/323 = 32.8 cm3. The increase 2.8 cm3 divided by 30 is about 0.093.
2C2H2(g) + 5O2(g) → 4CO2(g) + 2H2O(g)
In the reaction above, the mass of carbon(IV)oxide produced on burning 78 g of ethyne is [C = 12, O = 16, H = 1]
Answer: A (264 g)
78 g ÷ 26 g/mol = 3 mol of ethyne. Each mole gives 2 mol CO2, so 6 mol × 44 g = 264 g.
The ion that can be used as an oxidizing agent is
Answer: B (Fe3+)
An oxidising agent gains electrons. Fe3+ readily accepts an electron to become Fe2+. F− cannot gain more electrons, and Ca2+ is very hard to reduce.
Trioxonitrate(V) acid is not used for preparing hydrogen gas from metals because it
Answer: A (is strongly oxidizing)
HNO3 is a strong oxidising agent: any hydrogen formed is oxidised to water, and oxides of nitrogen are given off instead.
H2(g) + Br2(g) → 2HBr(g)
The reaction above is carried out at 25°C. If ΔH is −72 kJ mol−1 and ΔS is − 106 J mol−1 K−1, the reaction will
Answer: B (proceed spontaneously at the given temperature)
ΔG = ΔH − TΔS = −72 − (298 × −0.106) = −72 + 31.6 = −40.4 kJ mol−1. A negative ΔG means it proceeds spontaneously at 25°C.
Zinc and carbon rods are used as anode and cathode respectively in a
Answer: A (Leclanche cell)
The Leclanché (dry) cell has a zinc case as the negative electrode and a central carbon rod as the positive electrode.
The solution that will conduct the highest amount of electricity is
Answer: B (2.0 mol dm−3 of hydrochloric acid)
HCl is a strong acid (fully ionised) and the 2.0 mol dm−3 solution has the most ions, so it conducts best.
In which of the following is the oxidation number of sulphur equal to −2?
Answer: C (H2S)
In H2S each H is +1, so S is −2. In SO3 it is +6, in SO2 +4 and in S8 0.
In the electrolysis of CuSO4(aq) using platinum electrodes, the reaction at the anode is
Answer: B (4OH− − 4e− → 2H2O + O2)
With inert electrodes, OH− ions are discharged in preference to SO42− at the anode, losing electrons to form water and oxygen gas.
If the heat of combustion of hydrogen is −285.8kJ, what is the heat of formation of water?
Answer: C (−285.8 kJ)
Burning one mole of hydrogen (H2 + ½O2 → H2O) is the same reaction as forming one mole of water from its elements, so both are −285.8 kJ.
5SO2(g) + 2KMnO4(aq) + 2H2O(l) → K2SO4(aq) + 2MnSO4(aq) + 2H2SO4(aq)
In the reaction above, the products give a
Answer: D (colourless solution)
SO2 reduces purple MnO4− to almost colourless Mn2+; all the products are soluble, so a colourless solution forms.