49 questions. Try each one, then open the answer to check yourself and read the explanation.
Which of the following substances is not a homogeneous mixture?
Answer: C (Flood water)
A homogeneous mixture is the same all through. Flood water has mud and other particles suspended in it that settle out, so it is heterogeneous; sea water, soft drinks and ink are uniform.
There is a large temperature interval between the melting point and the boiling point of a metal because
Answer: C (melting does not break the metallic bond but boiling does)
When a metal melts, the atoms can slide past each other but the sea of electrons still holds them together. Boiling must separate the atoms completely, which needs far more energy, so the boiling point is much higher.
How many moles of (H+) are there in 1 dm3 of 0.5 M solution of H2SO4?
Answer: B (1.0 mole)
1 dm3 of 0.5 M acid contains 0.5 mol of H2SO4. Each mole gives 2 moles of H+, so there is 1.0 mole of H+.
wH2SO4 + xAl(OH)3 → yH2O + zAl2(SO4)3. The respective values of w, x, y and z in the equation above are
Answer: C (3,2,6 and 1)
3H2SO4 + 2Al(OH)3 → 6H2O + Al2(SO4)3: 2 Al, 3 SO4 and 12 H balance on both sides.
A given mass of gas occupies 2 dm3 at 300 K. At what temperature will its volume be doubled keeping the pressure constant?
Answer: D (600 K)
Charles' law: at constant pressure volume is proportional to kelvin temperature. Doubling the volume needs double the temperature: 2 × 300 K = 600 K.
If 100 cm3 of oxygen pass through a porous plug in 50 seconds, the time taken for the same volume of hydrogen to pass through the same porous plug is [O = 16, H = 1].
Answer: B (12.5 s)
By Graham's law time is proportional to √(molar mass): t = 50 × √(2/32) = 50 × 0.25 = 12.5 s.
Which of the following is a measure of the average kinetic energy of the molecules of a substance?
Answer: D (Temperature)
Temperature measures the average kinetic energy of the particles: the hotter the substance, the faster its particles move.
An increase in temperature causes an increase in the pressure of a gas in a fixed volume due to an increase in the
Answer: D (number of collisions between the gas molecules and the walls of the container)
Gas pressure comes from molecules hitting the container walls. Hotter molecules move faster and hit the walls more often and harder, so pressure rises.
The nucleus of the isotope tritium, contains
Answer: C (two neutrons and one proton)
Tritium is hydrogen-3: 1 proton (as for all hydrogen) and 3 − 1 = 2 neutrons. Electrons are outside the nucleus.
How many lone pairs of electrons are there on the central atom of the H2O molecule?
Answer: B (2)
Oxygen has six valence electrons. Two are shared in the O–H bonds and the other four form two lone pairs, which is why water is bent.
147N + X → 178O + 11H. In the above reaction, X is a
Answer: B (helium atom)
Mass numbers: 14 + a = 17 + 1, so a = 4. Atomic numbers: 7 + z = 8 + 1, so z = 2. X is 42He, a helium nucleus.
Four elements P, Q, R and S have 1, 2, 3 and 7 electrons in their outermost shells respectively. The element which is unlikely to be a metal is
Answer: D (S)
Metals usually have 1–3 outer electrons, which they lose. An element with 7 outer electrons gains one electron and is a non-metal (a halogen).
The pollutants that are likely to be present in an industrial environment are
Answer: A (H2S, SO2 and oxides of nitrogen)
Burning fuels and refining in factories release hydrogen sulphide, sulphur(IV) oxide and oxides of nitrogen, the typical industrial air pollutants.
Which of the following gases dissolves in water vapour to produce acid rain during rainfall?
Answer: D (Sulphur (IV) oxide)
Sulphur(IV) oxide dissolves in rain water to form sulphurous (and then sulphuric) acid, causing acid rain.
Water for town supply is chlorinated to make it free from
Answer: B (bacteria)
Chlorine kills germs (bacteria) in water. It does not remove hardness.
On which of the following is the solubility of a gaseous substance dependent? I. Nature of solvent II. Nature of solute III. Temperature IV. Pressure
Answer: A (I, II, III and IV)
How much gas dissolves depends on which gas it is and which solvent is used (ammonia dissolves far better in water than oxygen), and also on temperature and pressure.
An emulsion paint consists of
Answer: C (solid particles dispersed in liquid)
Emulsion paint is tiny solid particles of pigment and polymer binder spread through water, a liquid. (A true emulsion of liquid in liquid is not what the paint is.)
A sample of orange juice is found to have a pH of 3.80. What is the concentration of the hydroxide ion in the juice?
Answer: B (6.3 × 10−11)
pOH = 14 − 3.80 = 10.20, so [OH−] = 10−10.2 ≈ 6.3 × 10−11 mol/dm3.
Arrange HCl, CH3COOH, C6H5CH3 in order of increasing conductivity.
Answer: C (C6H5CH3, CH3COOH, HCl)
Methylbenzene is a non-electrolyte (no ions), ethanoic acid is a weak electrolyte (few ions) and HCl is a strong electrolyte (fully ionised).
Which of these is an acid salt?
Answer: C (NaHS)
An acid salt still has a replaceable hydrogen from the acid. NaHS comes from H2S with only one H replaced. Alum is a double salt and CuCO3.Cu(OH)2 is a basic salt.
How many grams of H2SO4 are necessary for the preparation of 0.175 dm3 of 6.00 M H2SO4? [S = 32.06, O = 16.00, H = 1.00].
Answer: B (103.0 g)
Moles = 6.00 × 0.175 = 1.05 mol. Mass = 1.05 × 98.06 ≈ 103.0 g.
Copper (II) tetraoxosulphate (VI) solution is electrolysed using carbon electrodes. Which of the following are produced at the anode and cathode respectively?
Answer: B (Oxygen and copper)
With inert carbon electrodes, OH− ions are discharged at the anode to give oxygen, and Cu2+ ions are discharged at the cathode to give copper.
Calculate the mass, in kilograms, of magnesium produced by the electrolysis of magnesium (II) chloride in a cell operating for 24 hours at 500 amperes. [1 Faraday = 96,500 C mol−1, Mg = 24].
Answer: B (5.4)
Charge = 500 × 24 × 3600 = 43 200 000 C. Mg2+ needs 2 × 96 500 C per 24 g, so mass = 43 200 000 × 24 ÷ 193 000 ≈ 5372 g ≈ 5.4 kg.
MnO2 + 2Cl− + 4H+ → Mn2+ + Cl2 + 2H2O. The changes in oxidation numbers when the manganese, chloride and hydrogen ions react according to the above equation are respectively
Answer: C (−2, 1, 0)
Mn goes from +4 to +2 (change −2), Cl goes from −1 to 0 (change +1) and H stays at +1 (change 0).
2S2O32− + I2 → S4O62− + 2I−. In the reaction above, the oxidising agent is
Answer: B (I2)
Iodine goes from 0 in I2 to −1 in I−, so it is reduced. The substance reduced is the oxidising agent.
In what way is equilibrium constant for the forward reaction related to that of the reverse reaction?
Answer: B (The product of the two is expected to be one.)
Writing the reverse reaction turns the expression upside down, so Kreverse = 1/Kforward. Multiplying them gives 1.
Which of the following equilibria shows little or no net reaction when the volume of the system is decreased?
Answer: A (H2(g) + I2(g) ⇌ 2HI(g))
Decreasing the volume raises the pressure, which favours the side with fewer gas molecules. H2 + I2 ⇌ 2HI has 2 moles of gas on each side, so it does not shift.
For a general equation of the nature xP + yQ ⇌ mR + nS, the expression for the equilibrium constant is
Answer: C ([R]m[S]n/[P]x[Q]y)
K = concentrations of products ÷ concentrations of reactants, each raised to the power of its coefficient: [R]m[S]n/[P]x[Q]y.
Which of these statements is TRUE about carbon (IV) oxide?
Answer: D (It supports the burning of magnesium to produce magnesium oxide.)
CO2 puts out most fires, but burning magnesium is hot enough to take the oxygen from it: 2Mg + CO2 → 2MgO + C. CO2 is only slightly soluble and forms a weak acid.
In the experiment above (Z is heated in the flask and nitrogen (I) oxide is collected over water), Z can be
Answer: C (a solution of sodium trioxonitrate (V) and ammonium chloride)
Heating ammonium trioxonitrate(V) gives nitrogen(I) oxide: NH4NO3 → N2O + 2H2O. A mixture of sodium trioxonitrate(V) and ammonium chloride produces ammonium trioxonitrate(V) when heated, so it gives N2O.
Which of the following combination of gases is used for metal welding? I. Oxygen and ethyne. II. Hydrogen and ethyne III. Hydrogen and oxygen IV. Ethyne, hydrogen and oxygen
Answer: C (I and III)
A welding flame needs a fuel burning in pure oxygen. The oxy-acetylene flame (I) and the oxy-hydrogen flame (III) are both used.
Which of the following oxides of nitrogen is unstable in air?
Answer: B (NO)
Nitrogen(II) oxide reacts at once with oxygen in air to form brown NO2: 2NO + O2 → 2NO2.
The gas formed when ammonium trioxonitrate (V) is heated with sodium hydroxide is
Answer: D (ammonia)
Any ammonium salt heated with an alkali gives off ammonia: NH4NO3 + NaOH → NaNO3 + NH3 + H2O.
Safety matches contain sulphur and
Answer: A (potassium trioxochlorate (V))
A safety match head contains sulphur with potassium trioxochlorate(V) (KClO3) as the oxygen supplier. The red phosphorus is on the side of the box.
Addition of an aqueous solution of barium chloride to the aqueous solution of a salt gives a white precipitate. The salt is likely to be a
Answer: B (carbonate)
Barium ions form insoluble white barium trioxocarbonate(IV) with carbonate ions: Ba2+ + CO32− → BaCO3. Barium nitrate, chloride and sulphide are soluble, so they give no precipitate.
Sodium hydroxide solution can be conveniently stored in a container made of
Answer: D (copper)
Lead, zinc and aluminium are amphoteric metals that dissolve in sodium hydroxide. Copper does not react with alkali.
Which of the following is NOT used as a raw material in the Solvay process?
Answer: D (Sodium trioxocarbonate (IV).)
The Solvay process uses brine, ammonia and limestone to make sodium trioxocarbonate(IV), so Na2CO3 is the product, not a raw material.
Duralumin consists of aluminium, copper,
Answer: D (manganese and magnesium.)
Duralumin is a light, strong alloy of mainly aluminium with small amounts of copper, manganese and magnesium; it is used in aircraft.
CaO(s) + H2O(l) → Ca(OH)2(s) ΔH = −65 kJ. The process represented by the above equation is known as
Answer: B (slaking)
Adding water to quicklime (CaO) to form slaked lime, Ca(OH)2, is called slaking; it gives out a lot of heat.
The carbon atoms in ethene are
Answer: C (sp2 hybridized)
Each carbon in ethene forms three σ bonds (trigonal planar) plus one π bond, so it is sp2 hybridized.
CH3—C(CH2CH3) = CH—CH2—CH(CH3)—CH3
The IUPAC name for the hydrocarbon above is
Answer: D (3,6 - dimethylhept - 3 - ene.)
The longest chain runs through the ethyl group and has 7 carbons. Numbering from the ethyl end puts the double bond at C3 and methyl groups at C3 and C6: 3,6-dimethylhept-3-ene.
Which of the following compounds is a secondary alkanol?
Answer: A (CH3CH2CH(OH)CH3)
In a secondary alkanol the –OH carbon is joined to two other carbons. In butan-2-ol (A) it is; B is primary, D is tertiary and C is an ether.
Which of the following compounds reacts with sodium metal as well as silver and copper salts?
Answer: C (CH3C ≡ CH)
Only a terminal alkyne has a hydrogen on a C≡C carbon, which is acidic enough to be replaced by sodium, silver or copper. Propyne is a terminal alkyne; but-2-yne is not.
Which of the following are isomers?
Answer: A (Ethanol and dimethyl ether)
Isomers share a molecular formula but differ in structure. Ethanol (CH3CH2OH) and dimethyl ether (CH3OCH3) are both C2H6O.
The functional group present in an organic compound which gives bubbles on treatment with a saturated solution of NaHCO3 is
Answer: D (carboxyl group.)
Carboxylic acids (–COOH) are acidic enough to react with NaHCO3, releasing bubbles of CO2.
The characteristic reaction of carbonyl compounds is
Answer: C (addition)
The C=O double bond in aldehydes and ketones is polar, so reagents such as HCN and NaHSO3 add across it: nucleophilic addition.
An organic compound containing 40.1% carbon and 6.67% hydrogen has an empirical formula of
Answer: C (CH2O)
Oxygen = 100 − 40.1 − 6.67 = 53.23%. Moles: C 40.1/12 = 3.34, H 6.67/1 = 6.67, O 53.23/16 = 3.33, a ratio of 1 : 2 : 1, so CH2O.
Alkanals can be differentiated from alkanones by reaction with
Answer: D (Tollen's reagent.)
Alkanals are easily oxidised and give a silver mirror with Tollen's reagent; alkanones do not. Both react with 2,4-DNPH, HCN and NaHSO3.
An example of a polysaccharide is
Answer: D (starch)
Starch is a polymer of many glucose units, i.e. a polysaccharide. Dextrose (glucose) and mannose are monosaccharides.