Chemistry Questions and Answers

Answer: D

Caesium is the most electropositive of the four.

Electropositive character - the tendency to lose an electron - increases down a group as the atom grows larger and the outer electron is more shielded, and decreases across a period. Cs lies lowest in Group 1 among these, so its ionisation energy is the smallest. Francium is more electropositive still but is radioactive and vanishingly rare.

Answer: B

Soda glass is so called because it is made using soda, that is sodium carbonate.

It is a soda-lime-silica glass, melted from sand, sodium carbonate and limestone in roughly the proportions 75:15:10. The soda lowers the melting point of silica from about 1,700 °C to a workable temperature, and the lime keeps the glass from dissolving in water.

Answer: B

Such atoms are isotopes.

They have the same atomic number, so they are the same element, but different mass numbers because the neutron count differs. Carbon-12, carbon-13 and carbon-14 are examples.

Answer: A

Protons and electrons are equal in number in a neutral atom.

The proton carries \(+1.6\times10^{-19}\ \mathrm{C}\) and the electron exactly the opposite, so equal numbers make the atom electrically neutral. The neutron count varies between isotopes and need not match either.

Answer: B

Alum is used in the purification of water.

Potash alum, \(\mathrm{K_2SO_4\cdot Al_2(SO_4)_3\cdot 24H_2O}\), releases \(\mathrm{Al^{3+}}\), whose high charge neutralises the negative charge on suspended clay particles so that they coagulate and settle. It is also used to stop bleeding from shaving cuts, for the same coagulating reason.

Answer: C

Cathode rays are a stream of electrons.

J.J. Thomson showed in 1897 that they are deflected by both electric and magnetic fields towards the positive plate, so they are negatively charged particles, and that their \(e/m\) ratio is the same whatever gas or electrode material is used - proving them a universal constituent of matter.

Answer: B

Zymase converts glucose to ethyl alcohol.

Secreted by yeast, it catalyses \[\mathrm{C_6H_{12}O_6 \rightarrow 2\,C_2H_5OH + 2\,CO_2}\] Invertase first splits sucrose into glucose and fructose, diastase converts starch to maltose, and maltase maltose to glucose - zymase completes the chain.

Answer: C

These are isotones.

They share the neutron number but differ in protons, so both the element and the mass number differ - \(^{14}_{6}\mathrm{C}\), \(^{15}_{7}\mathrm{N}\) and \(^{16}_{8}\mathrm{O}\) each have 8 neutrons.

Answer: C

Glenn T. Seaborg is credited with the discovery of the transuranic elements.

With his co-workers at Berkeley he identified plutonium, americium, curium, berkelium and californium among others, and shared the 1951 Nobel Prize for the work. Element 106, seaborgium, is named after him - the only element named for a living person at the time.

Answer: B

Dust is removed by electrophoresis, in the Cottrell precipitator.

Smoke is a colloidal sol of solid particles carrying an electric charge. Passing the flue gas between electrodes at a high potential difference discharges the particles, so they lose their mutual repulsion, coagulate and fall - and only the clean gas leaves the chimney.