Chemistry Questions and Answers

Answer: C

This is Henry's law.

\[p = K_H\, x\] where \(x\) is the mole fraction of the dissolved gas and \(p\) its partial pressure above the liquid. It explains why a fizzy drink releases gas when opened, and why divers ascending too quickly suffer decompression sickness as dissolved nitrogen comes out of the blood.

Answer: B

Ethylene ripens green fruit artificially.

It is the plant's own ripening hormone, and a few parts per million in a closed chamber will start the breakdown of chlorophyll and the conversion of starch to sugar. Because it is a gas, one ripening fruit hastens the ripening of others beside it.

Answer: D

The \(\mathrm{Zn^{2+}}\) ion contains 35 neutrons.

Zinc has \(Z=30\) and a mass number of 65, so \[N = A - Z = 65 - 30 = 35\] Forming the dipositive ion removes two electrons; the nucleus is untouched, so the neutron count is unchanged.

Answer: C

Milk is a poor source of vitamin C.

It is rich in calcium, high-quality protein and lactose, and supplies vitamins A, D and the B group, but contains very little ascorbic acid - and pasteurisation destroys most of what there is. This is why an infant fed only on milk needs a separate source of vitamin C.

Answer: A

The order is \(\mathrm{N^{3-} > O^{2-} > F^- > Na^+}\).

All four are isoelectronic, each having 10 electrons, so the size depends only on the nuclear charge pulling them in: \[\mathrm{N}\ (Z=7) < \mathrm{O}\ (8) < \mathrm{F}\ (9) < \mathrm{Na}\ (11)\] The larger the nuclear charge for the same electron count, the smaller the ion - so radius falls as \(Z\) rises.

Answer: B

Glass is a homogeneous mixture of metallic silicates.

Ordinary soda-lime glass is a fused mixture of sodium and calcium silicates in silica, of no fixed composition, and it is uniform throughout with no visible boundaries. Being amorphous, it has no sharp melting point.

Answer: A

Silver's symbol is Ag.

It comes from the Latin argentum. Several symbols are Latin rather than English: Au from aurum for gold, Fe from ferrum, Na from natrium, K from kalium and Pb from plumbum.

Answer: C

Xenon is called the stranger gas.

The name comes from the Greek xenos, meaning stranger, and was given by Ramsay and Travers in 1898 because it was found only in vanishingly small traces in liquid air. It is also the noble gas that most readily forms compounds, such as \(\mathrm{XeF_4}\).

Answer: B

The liver converts sugars into glycogen.

Glucose absorbed from the gut is polymerised to glycogen and stored, a process called glycogenesis and driven by insulin. When blood glucose falls, glucagon reverses it and the glycogen is broken down again.

Answer: C

Polonium has the greatest number of isotopes, some thirty-three of them.

All are radioactive; polonium has no stable isotope at all. Heavy elements have many possible neutron numbers, none of which gives a stable nucleus, so the count of known isotopes is large.