50 questions. Try each one, then open the answer to check yourself and read the explanation.
An element X has 127 neutrons and 82 electrons. Its atomic number is
Answer: D (82)
A neutral atom has as many protons as electrons, so X has 82 protons. The atomic number is the number of protons, 82.
When a bottle of Coca-Cola is opened, bubbles of gas evolve. The gas is
Answer: C (carbon dioxide)
Fizzy drinks are made by dissolving carbon dioxide under pressure. When the bottle is opened the pressure falls and the CO2 comes out as bubbles.
Which of the following is the electronic configuration of sodium? (Atomic number of Na = 11)
Answer: C (1s2 2s2 2p6 3s1)
Sodium has 11 electrons: 2 fill 1s, 2 fill 2s, 6 fill 2p and the last one goes into 3s, giving 1s2 2s2 2p6 3s1.
Methane is a member of the homologous series called
Answer: D (alkanes)
Methane, CH4, is the first member of the alkanes (general formula CnH2n+2).
When a glowing splint is inserted into the mouth of a jar containing a gas, the splint is extinguished. The gas gives a white precipitate when passing into barium hydroxide. The gas is
Answer: E (carbondioxide)
Carbon dioxide does not support burning, so it puts out the splint, and it reacts with barium hydroxide to form a white precipitate of barium carbonate.
An example of a strong electrolyte is
Answer: D (sodium formate)
Sodium formate is a salt, so it is fully ionised in water and is a strong electrolyte. Formic acid is a weak acid, and the other three are non-electrolytes.
The oxidation state of manganese in KMnO4 is
Answer: D (+7)
K is +1 and four O atoms give −8, so Mn + 1 − 8 = 0 and Mn = +7.
For iron to rust, there should be present
Answer: D (oxygen and moisture)
Rusting needs both oxygen (air) and water. Carbon dioxide speeds it up but is not required.
The mass number of an atom is
Answer: E (the sum of the numbers of protons and neutrons in the nucleus of the atom)
The mass number counts the particles in the nucleus: protons plus neutrons.
Sodium and potassium belong to the same group of the Periodic Table. This is because
Answer: D (both have identical electronic configuration)
Elements in the same group have the same outer-shell electron arrangement. Sodium (2,8,1) and potassium (2,8,8,1) each have one electron in the outer shell, which is what the option means by 'identical' configuration.
In the reaction of oxygen with hydrogen to produce water, which of the following statements is true?
Answer: E (One molecule of oxygen reacts with two molecules of hydrogen to give two molecules of water.)
The balanced equation is 2H2 + O2 → 2H2O: two molecules of hydrogen and one of oxygen give two molecules of water.
Oxidation is the process of
Answer: B (loss of electrons)
In electron terms, oxidation is loss of electrons (OIL RIG). The other options describe reduction.
The number of atoms in one mole of a substance is equal to
Answer: B (the Avogadro number)
One mole of an element contains 6.02 × 1023 atoms, the Avogadro number.
Which of the following statements is NOT true of electrovalent compounds?
Answer: D (The elements forming the compounds normally have their valency electrons in a shared state)
In electrovalent (ionic) compounds electrons are transferred, not shared. Sharing electrons describes covalent compounds.
If concentrated sulphuric acid is added to sugar and warmed gently, the sugar changes from white to brown and finally to a black mass of carbon. In this reaction, concentrated sulphuric acid is acting as
Answer: C (a dehydrating agent)
The acid removes the elements of water (H and O in a 2:1 ratio) from the sugar, leaving carbon. That is dehydration.
In the reaction C + 2HNO3 → CO2 + NO2 + NO + H2O nitric acid is acting as
Answer: C (an oxidizing agent)
Carbon goes from 0 to +4 (oxidised) while nitrogen goes from +5 to +4 and +2 (reduced), so nitric acid is the oxidizing agent.
The brown coloration in the nitric acid prepared in the laboratory can be removed by
Answer: B (bubbling air through the acid)
The brown colour is dissolved nitrogen(IV) oxide. Blowing air through the acid sweeps it out (and oxidises it back to the acid).
Which of the following processes takes place during electrolysis?
Answer: D (Negative ions are discharged at the anode by losing sufficient electrons to become neutral)
Anions move to the anode and give up their extra electrons there, becoming neutral atoms or molecules.
In the preparation of ammonia, which of the following is used as the drying agent?
Answer: A (CaO)
Ammonia is basic, so it is dried with quicklime (CaO). Acidic driers react with it and CaCl2 forms a complex with it.
Which of the following can have an isomer?
Answer: B (C4H10)
C4H10 can be a straight chain (butane) or branched (2-methylpropane). The smaller alkanes and ethene have only one possible structure.
Allotropes are elements having
Answer: A (different physical but the same chemical properties)
Allotropes are different forms of the same element, e.g. diamond and graphite: their physical properties differ but they react the same way.
A polymerization reaction is one in which
Answer: A (small molecules form giant molecules)
In polymerization many small molecules (monomers) join to make one very large molecule (a polymer).
Na2CO3 + 2HCl → 2NaCl + H2O + CO2. Using the above equation, what volume of carbondioxide, measured at s.t.p is liberated when 53 g of sodium carbonate is dissolved in hydrochloric acid? (1 mole of gas occupies 22.4 dm3 at s.t.p) (Na = 23, C = 12, O = 16)
Answer: B (11.2 dm3)
Molar mass of Na2CO3 = 106 g, so 53 g is 0.5 mol. It gives 0.5 mol CO2 = 0.5 × 22.4 = 11.2 dm3.
When sodium nitrite dissolves in water, ΔH is positive. This means that
Answer: D (the reaction is endothermic)
A positive ΔH means heat is taken in from the surroundings, which is an endothermic change.
If an organic compound decolorizes bromine water then the compound is
Answer: C (unsaturated)
Bromine adds across C=C or C≡C bonds, removing its colour, so decolorizing bromine water shows the compound is unsaturated.
When air is compressed
Answer: D (its temperature increases)
Work is done on the gas when it is squeezed, so its molecules move faster and its temperature rises (a bicycle pump gets warm). Its density increases, not decreases.
Fats and oils are
Answer: C (condensation products of long-chain fatty acids and glycerol)
Fats and oils are esters formed when fatty acids react with glycerol, losing water; reactions that eliminate water are condensation reactions.
Which of the following statements about phosphorus is NOT correct?
Answer: B (Phosphorus is obtained by oxidation of phosphates)
Phosphorus is extracted by reducing calcium phosphate with coke (and sand) in an electric furnace, not by oxidation. Yellow phosphorus is very easily ignited, so E is true.
If 48,000 coulombs of electricity are required to discharge 0.5 mole of sodium from a molten sodium chloride mass, then the number of coulombs required to discharge 2 moles of lead from molten lead (II) chloride is
Answer: D (384,000)
Na+ needs 1 mol of electrons per mole, so 1 mol of electrons is 96,000 C here. Pb2+ needs 2 mol of electrons per mole, so 2 mol Pb needs 4 × 96,000 = 384,000 C.
28.8 cm3 of nitrogen at 15°C is cooled to 0°C at constant pressure, the new volume of nitrogen is
Answer: C (27.3 cm3)
Charles' law: V2 = 28.8 × 273/288 = 27.3 cm3 (temperatures in kelvin).
In an experiment 5.00 g of a metal gave 10.59 g of its chloride. In another experiment, 1.50 g of the same metal combined with 1.68 g of chlorine. The above data illustrates
Answer: B (Law of Definite Proportion)
Chlorine per gram of metal is 5.59/5.00 = 1.12 in the first experiment and 1.68/1.50 = 1.12 in the second. The same fixed ratio shows the law of definite proportions.
The products of the reaction between dilute sulphuric acid and sodium thiosulphate crystals are
Answer: C (Na2SO4 + SO2 + S + H2O)
Na2S2O3 + H2SO4 → Na2SO4 + SO2 + S + H2O; the yellow sulphur precipitate is the well-known sign of this reaction.
The following compounds are given with their corresponding boiling points
Compound I: 14°C
Compound II: 24°C
Compound III: 0°C
Compound IV: 120°C
Compound V: −2°C
From the above information, indicate which of the following is correct
Answer: D (Three of the compounds are gaseous at 20°C)
A substance is a gas at 20°C if its boiling point is below 20°C. That is true for I (14°C), III (0°C) and V (−2°C): three compounds.
Which of the following is NOT a true statement of the Kinetic Theory of Gases?
Answer: D (Every molecule has the same kinetic energy at a particular temperature)
Molecules in a gas have a spread of speeds and energies; only their average kinetic energy is fixed by the temperature.
The electronic configuration of elements X and Y are X = 2, 8, 6; Y = 2, 8, 7. The bond in the compound formed by X and Y is expected to be
Answer: B (covalent)
X (sulphur) and Y (chlorine) are both non-metals that need electrons, so they share electrons and form covalent bonds.
5 cm3 of a saturated solution of sodium chloride at 30°C gave, on careful evaporation, 1.95 g of solid salt. The solubility of sodium chloride at 30°C is (Na = 23, Cl = 35.5)
Answer: D (6.67 mole dm−3)
1.95 g in 5 cm3 is 390 g per dm3. Dividing by the molar mass 58.5 g gives 6.67 mol dm−3.
In the extraction of iron, which of the following reactions does NOT take place in the blast furnace?
Answer: B (2Fe2O3 + 3C → 4Fe + 3CO2)
In the blast furnace the ore is reduced by carbon monoxide, not directly by carbon to CO2. The other reactions make the CO and remove the sand impurity as slag.
Pure sulphuric acid is a liquid of 1.84 density. What volume of it would be required to prepare 250 cm3 of 0.2 M solution? (H = 1, S = 32, O = 16)
Answer: B (2.66)
Moles needed = 0.250 × 0.2 = 0.05 mol, which is 0.05 × 98 = 4.9 g. Volume = mass/density = 4.9/1.84 = 2.66 cm3.
What mass of sodium carbonate is in 500 cm3 of 0.1 molar sodium carbonate solution? (Na = 23, C = 12, O = 16)
Answer: B (5.3 g)
Moles = 0.5 dm3 × 0.1 mol dm−3 = 0.05 mol; mass = 0.05 × 106 = 5.3 g.
Which of the following compounds and elements would sublime on exposure to the atmosphere?
Answer: D (Iodine)
Iodine crystals turn straight into violet vapour without melting, i.e. they sublime.
When hydrogen sulphide and sulphur dioxide are each passed in turn into a solution of potassium dichromate
Answer: E (only hydrogen sulphide deposits sulphur.)
Both gases reduce the dichromate (orange to green), but only H2S is oxidised to solid sulphur; SO2 is oxidised to sulphate ions in solution.
Which one of the following metals is not normally extracted by chemical reduction because of its position in the electrochemical series?
Answer: D (Potassium)
Potassium is very high in the electrochemical series, so carbon cannot reduce its compounds; it is extracted by electrolysis of the molten compound.
If 1 mole of aluminium contains 6 × 1023 atoms of aluminium, how many atoms are contained in 0.9 g of aluminium? (Al = 27)
Answer: C (2.0 × 1022)
0.9 g ÷ 27 g/mol = 1/30 mol; 1/30 × 6 × 1023 = 2.0 × 1022 atoms.
4 g each of aluminium foil and aluminium powder were introduced respectively into flasks P and Q. Flask P was treated with warm bench sodium hydroxide and all the aluminium dissolved in one hour. Flask Q was treated with cold sodium hydroxide and all the aluminium dissolved in 10 minutes. What was responsible for Q reacting faster than P?
Answer: E (Q has a greater surface area for the reaction than P.)
Both flasks held the same mass of aluminium, but powder exposes far more surface to the alkali than foil, so Q reacted faster even though it was cold.
The IUPAC name for (CH3)2CH—CH2—CH3 is
Answer: C (2-methylbutane)
The longest chain has four carbons (butane) and the CH3 branch sits on carbon 2 when numbered from the nearer end, so it is 2-methylbutane.
What happens when the nitrates of potassium, calcium, zinc and copper are separately heated?
Answer: E (The nitrates of calcium, zinc and copper decompose to their oxides.)
Potassium nitrate (a very reactive metal) gives the nitrite and oxygen; the nitrates of calcium, zinc and copper give the metal oxide, nitrogen(IV) oxide and oxygen.
The scale formation in a kettle used for boiling water is caused by the presence in water of
Answer: C (calcium hydrogen carbonate)
Dissolved calcium hydrogen carbonate decomposes on boiling to insoluble calcium carbonate, which forms the scale (fur) in kettles.
An efflorescent compound is a substance that
Answer: C (gives out water to the atmosphere)
An efflorescent substance (e.g. washing soda crystals) loses water of crystallization to the atmosphere simply on standing in air, without heating.
Which of the following represents a precipitation reaction?
Answer: D (Na2SO4 + Pb(NO3)2 → PbSO4 + 2NaNO3)
Lead(II) sulphate is insoluble, so mixing the two soluble salts gives a solid precipitate of PbSO4.
The general formula of an alkyl halide (which X represents the halide) is
Answer: B (CnH2n+1X)
An alkyl group is an alkane minus one H, CnH2n+1, so an alkyl halide is CnH2n+1X.