Chemistry Questions and Answers

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.

Answer: C

Metabolising one gram of fat releases about 39 kJ, roughly 9 kcal.

Carbohydrate and protein yield about 17 kJ (4 kcal) per gram, so fat provides more than twice as much energy for the same mass. That density is why the body stores its reserves as fat rather than as glycogen.

Answer: D

Ozone is diamagnetic.

All the electrons in \(\mathrm{O_3}\) are paired, so it has no permanent magnetic moment and is weakly repelled by a magnetic field. Ordinary oxygen, \(\mathrm{O_2}\), is the opposite: it has two unpaired electrons in its antibonding \(\pi^*\) orbitals and is paramagnetic.

Answer: C

The answer is 800 g.

Depression of freezing point: \[\Delta T_f = K_f\, m \Rightarrow m = \frac{\Delta T_f}{K_f} = \frac{6}{1.86} = 3.226\ \mathrm{mol\,kg^{-1}}\]

For 4 kg of water, \[n = 3.226 \times 4 = 12.90\ \text{mol}\]

\[w = n \times M = 12.90 \times 62 = 800\ \mathrm{g}\]

Answer: B

The process is smelting.

The ore is heated with a flux and a reducing agent above the melting point of the metal, so the metal collects as a molten layer and the impurities float off as slag. Roasting and calcination are carried out below the melting point and only convert the ore to the oxide.