Chemistry Questions and Answers

Answer: C

Alloys of mercury are called amalgams.

Mercury dissolves most metals at room temperature, and dental amalgam - mercury with silver, tin and copper - is the familiar example. Iron is the notable exception, which is why mercury can be stored and shipped in iron flasks.

Answer: B

Hydrogen is used to make vanaspati.

Passed through the warm oil over a nickel catalyst, it adds across the carbon–carbon double bonds, converting the unsaturated liquid oil into a saturated semi-solid fat. The process is called hydrogenation, or hardening of oils.

Answer: C

Table salt is sodium chloride, NaCl.

It is mined as rock salt or obtained by evaporating sea water, and is the source of the chloride the stomach needs for hydrochloric acid, as well as of the sodium needed for nerve conduction. Iodised salt carries added potassium iodate to prevent goitre.

Answer: B

Caesium is the most electropositive of these.

Electropositive character - the readiness to lose an electron - increases down a group and decreases across a period, so among Ca, Cs, Na and Br the lowest member of Group 1 wins. Caesium's ionisation energy, \(376\ \mathrm{kJ\,mol^{-1}}\), is among the lowest of any element.

Answer: A

Boron behaves both as a metal and as a non-metal.

It is a metalloid: it has a lustrous, hard, semiconducting elemental form, yet its oxide \(\mathrm{B_2O_3}\) is acidic and its chemistry is dominated by covalent bonding. Argon is a noble gas, carbon a non-metal and mercury a metal.

Answer: A

Citric acid is the organic acid.

It is \(\mathrm{C_6H_8O_7}\), a carbon compound with three carboxyl groups, found in citrus fruit. Nitric, sulphuric and phosphoric acids contain no carbon and are mineral acids.

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

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: B

The atomic number gives the number of electrons in a neutral atom, because it equals the number of protons.

The proton count defines the element and is what the atomic number really counts; the electron count matches it only while the atom is uncharged. The number of nucleons is the mass number instead.

Answer: B

Aqua regia dissolves gold.

It is one part concentrated nitric acid to three parts concentrated hydrochloric acid. Neither acid alone will touch gold: the nitric acid oxidises it, and the chloride then locks the \(\mathrm{Au^{3+}}\) away as the chloroaurate complex, so the oxidation can continue. \[\mathrm{Au + 3HNO_3 + 4HCl \rightarrow HAuCl_4 + 3NO_2 + 3H_2O}\]