14 questions. Try each one, then open the answer to check yourself and read the explanation.
Pollution of water by crude oil can lead to
Answer: C (a decrease in oxygen content)
An oil film on the surface stops oxygen from dissolving into the water, so the dissolved oxygen falls and aquatic life suffers.
When a few drops of barium chloride is added to an unknown sample acidified with hydrochloric acid, a white precipitate insoluble in excess of the acid was obtained. The likely anion in the sample is
Answer: A (SO42−)
Barium sulphate is a white precipitate that does not dissolve in acid. Barium carbonate or sulphite would dissolve, giving off a gas.
Oxygen in air can be removed using
Answer: C (pyrogallol solution)
Alkaline pyrogallol absorbs oxygen. Lime water and caustic soda absorb carbon(IV) oxide instead.
Calculate the pH of a solution of 0.0001 moldm−3 hydrochloric acid
Answer: B (4)
HCl ionises fully, so [H+] = 10−4 mol/dm3 and pH = −log(10−4) = 4.
Which of the following dry agents is NOT suitable for drying hydrogen sulphide?
Answer: A (CaO)
H2S is an acidic gas, so it would react with the basic drying agent CaO.
Diamond is used in making jewelry due to its
Answer: A (high refractive index)
Diamond's high refractive index makes it sparkle when cut and polished, which is why it is used in jewellery.
The presence of impurities in a solid will make the melting point to
Answer: A (decrease)
Impurities disturb the regular arrangement of particles in a solid, so it melts at a lower temperature and over a range.
The discovery that protons and neutrons are concentrated at the nucleus of an atom was postulated by
Answer: A (E. Rutherford)
Rutherford's alpha-particle scattering experiment showed that the mass and positive charge of an atom are packed into a tiny nucleus.
Which of the following is hydroscopic substance?
Answer: A (NaNO3)
Sodium nitrate absorbs moisture without dissolving (hygroscopic). MgCl2 and CaCl2 absorb so much water that they dissolve, so they are called deliquescent.
In a chemical reaction, when the energy of the colliding reactant particles is less than the activation energy, the reaction will
Answer: B (not occur)
Particles must collide with at least the activation energy to react; with less energy the collisions are not effective and no reaction occurs.
The monomer of natural rubber is
Answer: A (2-methylbuta- 1,3-diene)
Natural rubber is a polymer of isoprene, 2-methylbuta-1,3-diene. 2-chlorobuta-1,3-diene is the monomer of neoprene.
PCl5(l) ⇌ PCl3(l) + Cl2(g) ΔH = +ve
In the reaction above, the forward reaction is favoured by
Answer: D (increasing the temperature)
The forward reaction is endothermic (ΔH positive), so raising the temperature shifts the equilibrium to the right. A catalyst does not shift equilibrium.
Which of the following halogens is the most reactive?
Answer: D (F2)
Reactivity of halogens falls down the group; fluorine, the most electronegative element, is the most reactive.
A gas that forms a black precipitate with lead(II) ethanoate is
Answer: D (H2S)
H2S reacts with lead(II) ethanoate to form black lead(II) sulphide; this is the test for hydrogen sulphide.