Chemistry Questions and Answers

Answer: D

Ozone is diamagnetic.

All the electrons in \(\mathrm{O_3}\) are paired, so it has no permanent magnetic moment and is weakly repelled by a magnetic field. Ordinary oxygen, \(\mathrm{O_2}\), is the opposite: it has two unpaired electrons in its antibonding \(\pi^*\) orbitals and is paramagnetic.

Answer: D

Carbon monoxide is the most toxic of these.

It binds to haemoglobin about 240 times more strongly than oxygen does, forming carboxyhaemoglobin, so the blood can no longer carry oxygen. A few hundred parts per million can be fatal, and because the gas is colourless and odourless there is no warning.

Answer: A

Urea has the highest nitrogen content, about 46 per cent.

\(\mathrm{NH_2CONH_2}\) has a molar mass of 60 with 28 units of nitrogen: \[\frac{28}{60}\times 100 = 46.7\%\] Ammonium nitrate is 35 per cent, ammonium chloride 26 per cent and ammonium sulphate 21 per cent, which is why urea is the commonest nitrogenous fertiliser.

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: C

Air is a mixture.

Its gases are not chemically combined, keep their own properties and vary in proportion from place to place. They can be separated physically, by fractional distillation of liquid air.

Answer: B

Brass is an alloy of copper and zinc.

Typical brass is 60–90 per cent copper with the balance zinc. Bronze is copper with tin instead, and adding zinc to copper gives a metal that is harder than copper yet still easily machined and cast.

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: D

The hottest part of a gas flame is the non-luminous zone.

There the air supply is plentiful, combustion is complete, and the flame reaches about 1,500 °C while burning pale blue. The luminous yellow zone is cooler because combustion is incomplete, its light coming from glowing carbon particles, and the innermost dark zone is unburnt gas.

Answer: C

This is the photoelectric effect.

Einstein explained it in 1905 with \[h\nu = \phi + \frac{1}{2}mv^2_{max}\] where \(\phi\) is the work function. Below a threshold frequency no electrons are ejected however intense the light, which showed that light delivers its energy in quanta - the work that won him the Nobel Prize.

Answer: C

Sodium's symbol is Na.

It comes from the Latin natrium, itself from natron, the naturally occurring sodium carbonate the Egyptians used. Several elements known since antiquity carry Latin symbols in the same way: K for kalium, Fe for ferrum, Ag for argentum.