Chemistry Questions and Answers

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.

Answer: C

Both statements are correct.

The sign convention of thermodynamics is written from the system's point of view: work done on the system is positive, and work done by the system on the surroundings is negative. With this convention the first law reads \[\Delta U = q + w\]

Answer: A

Ozone is produced in photochemical smog.

Sunlight splits nitrogen dioxide from vehicle exhaust, \[\mathrm{NO_2 + h\nu \rightarrow NO + O},\qquad \mathrm{O + O_2 \rightarrow O_3}\] and the ozone then reacts with unburnt hydrocarbons to give PAN and aldehydes. Hydrocarbons and nitrogen oxides are the ingredients rather than the products.

Answer: C

Chlorine is the most commonly used bleaching agent.

In water it forms hypochlorous acid, \[\mathrm{Cl_2 + H_2O \rightarrow HCl + HOCl}\] which releases nascent oxygen and oxidises the coloured compound to a colourless one. Bleaching by chlorine is therefore permanent, unlike bleaching by sulphur dioxide, which works by reduction and reverses in air.

Answer: C

Silver iodide is used to produce artificial rain.

Its crystal lattice closely resembles that of ice, so supercooled droplets in a cloud freeze on it and grow heavy enough to fall. It is dispersed from aircraft or fired from the ground into a cloud that already holds enough moisture.