Chemistry Questions and Answers

Answer: D

The cyclotron is used for accelerating particles.

Lawrence's design of 1930 sends charged particles spiralling between two D-shaped electrodes in a magnetic field, with an alternating voltage across the gap giving them a push on each half-turn. The period of revolution \[T = \frac{2\pi m}{qB}\] is independent of speed, which is what lets a single fixed frequency keep accelerating them.

Answer: A

The positron's charge equals that on the proton.

The positron is the antiparticle of the electron: it has the electron's mass but a charge of \(+1.6\times10^{-19}\ \mathrm{C}\), the same magnitude and sign as the proton's. It was predicted by Dirac and found by Anderson in 1932.

Answer: D

Argon is the most abundant noble gas in the atmosphere, at 0.93 per cent by volume.

Nearly all of it is argon-40, formed by the radioactive decay of potassium-40 in the crust and released into the air. It is the third commonest atmospheric gas after nitrogen and oxygen.

Answer: B

The noble gases are monatomic.

Their outermost shells are already complete, so the atoms have no tendency to bond even to one another and exist as single atoms. Every other gaseous element - hydrogen, nitrogen, oxygen, the halogens - goes about in molecules.

Answer: A

Silica is the major component of glass.

Ordinary soda-lime glass is about 75 per cent \(\mathrm{SiO_2}\), with sodium carbonate to lower the melting point and limestone to make the product insoluble. Adding boron oxide instead gives borosilicate glass, which expands little on heating.

Answer: C

The mass number is the sum of the protons and neutrons in the nucleus.

It is always a whole number and never less than the atomic number, which counts only the protons. Atomic weight is an average over an element's natural isotopes and is usually fractional.

Answer: D

Dolomite contains both magnesium and calcium.

Its formula is \(\mathrm{CaMg(CO_3)_2}\). Magnesite is \(\mathrm{MgCO_3}\), calcite \(\mathrm{CaCO_3}\), and carnallite \(\mathrm{KCl\cdot MgCl_2\cdot 6H_2O}\), which has magnesium but no calcium.

Answer: D

Atoms are composed of electrons and nuclei.

The nucleus holds the protons and neutrons and almost all the mass; the electrons occupy the surrounding orbitals and determine chemical behaviour. Saying 'electrons and protons' leaves out the neutrons, which is why the fuller answer is the right one.

Answer: D

LiCl shows the greatest covalent character.

By Fajans' rules, covalent character increases when the cation is small and highly charged and the anion large and easily polarised. \(\mathrm{Li^+}\) is the smallest of these cations, so it distorts the chloride ion most strongly. This is why LiCl dissolves in organic solvents such as ethanol and acetone, while CsCl does not.

Answer: D

Cathode rays have both mass and charge.

They are electrons. They are deflected by electric and magnetic fields, which shows they carry charge, and they turn a light paddle-wheel placed in their path, which shows they carry momentum and therefore mass.