Chemistry Questions and Answers

Answer: D

Acid rain is caused by sulphur dioxide, carbon dioxide and oxides of nitrogen.

\(\mathrm{SO_2}\) and \(\mathrm{NO_x}\) from burning coal and from vehicle exhaust are oxidised and dissolve to give sulphuric and nitric acids, and \(\mathrm{CO_2}\) gives weak carbonic acid. Rain below about pH 5.6 is counted as acid rain.

Answer: B

For neutral atoms, the periodic trends in atomic size can be described like this
Atomic size decreases when going from left to right across a period,
Atomic size increases when going from top to bottom down a group.
Let's use these trends to try and figure out which atom would have the largest radius.
If you look at elements that are located in the same group, potassium will have a larger atomic radius when compared with sodium. Likewise, bromine will have a larger atomic radius when compared with chlorine.
Now focus on potassium and bromine. Since potassium is located at the start of period 3, and bromine at the end of the same period, potassium will have a larger atomic radius than bromine, and thus the largest atomic radius of the four given atoms.

Answer: A

Diamond is an element.

It is pure carbon, an allotrope in which every atom is \(sp^3\) hybridised and bonded tetrahedrally to four others. Graphite, fullerenes and graphene are other allotropes of the same element.

Answer: C

Acetic acid is the oldest known organic compound.

Vinegar, a dilute solution of it, has been made by fermenting wine since antiquity, and Jabir ibn Hayyan concentrated it by distillation in the eighth century. Urea is significant for a different reason - Wöhler's 1828 synthesis of it was the first laboratory preparation of an organic compound from inorganic material.

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.