Chemistry Questions and Answers

Answer: D

Aluminium is extracted from bauxite.

The ore is hydrated aluminium oxide with iron and silica impurities; the Bayer process purifies it to alumina, and the Hall–Héroult cell then reduces the alumina electrolytically in molten cryolite.

Answer: D

Chlorofluorocarbons were used in refrigerators.

Freons are non-toxic, non-flammable and easily liquefied, which made them nearly ideal refrigerants. They also destroy stratospheric ozone catalytically, and the Montreal Protocol of 1987 phased them out in favour of HFCs and hydrocarbons.

Answer: C

Petroleum is found in sedimentary rocks.

It forms from marine organic matter buried in fine-grained sediments and cooked over millions of years, then migrates upward through porous rock until an impermeable cap traps it. Igneous and metamorphic rocks form at temperatures that would destroy the hydrocarbons.

Answer: A

Nucleons are protons and neutrons.

They are the particles that make up the nucleus, and their total is the mass number. Electrons lie outside the nucleus and are not nucleons.

Answer: B

Oil of vitriol is sulphuric acid.

The name is alchemical: the acid was first made by distilling green vitriol, hydrated iron(II) sulphate, and its oily viscosity gave it the rest of the name. Aqua fortis is nitric acid and spirit of salt hydrochloric acid.

Answer: D

Kinetic energy increases with increasing temperature.

For an ideal gas the average translational kinetic energy per molecule is \[\bar{E} = \frac{3}{2}k_BT\] so it is directly proportional to the absolute temperature and independent of the gas's identity. Temperature is, in effect, a measure of that molecular motion.

Answer: C

Batteries hold sulphuric acid.

A lead-acid cell uses about 35 per cent \(\mathrm{H_2SO_4}\) as electrolyte: \[\mathrm{Pb + PbO_2 + 2H_2SO_4 \rightarrow 2PbSO_4 + 2H_2O}\] The acid is consumed on discharge, so the electrolyte's specific gravity falls - which is how a hydrometer reads a battery's state of charge.

Answer: C

Inherited traits are controlled by DNA molecules.

The sequence of bases along the DNA of a gene specifies the amino-acid sequence of a protein, and it is DNA that is copied and passed to the next generation. RNA carries the message and enzymes do the work, but neither is the store of heredity.

Answer: B

The difference lies at the 2nd carbon of the sugar.

RNA contains ribose, which has a hydroxyl group at C-2; DNA contains 2-deoxyribose, which has only a hydrogen there. That missing \(\mathrm{-OH}\) makes DNA far more resistant to hydrolysis, which is why it, and not RNA, stores heredity.

Answer: D

Aluminium is the most abundant metal in the earth's crust, at about 8 per cent by mass.

Iron follows at about 5 per cent, then calcium, sodium, potassium and magnesium. Overall the crust's commonest elements are oxygen (46 per cent) and silicon (28 per cent), neither of which is a metal.