Chemistry Questions and Answers

Answer: A

Faraday's laws concern electrolysis.

The first states that the mass deposited is proportional to the charge passed, \(m = Zq\); the second that for the same charge, the masses of different substances are in the ratio of their equivalent weights. One faraday, \(96{,}500\ \mathrm{C}\), deposits one gram equivalent.

Answer: C

The noble gases are both colourless and odourless.

Being monatomic with complete outer shells, they have no low-lying electronic transitions in the visible range and no chemical interaction with the smell receptors. In a discharge tube they do glow - neon red, argon violet - but that is excited emission, not colour.

Answer: D

Chlorofluorocarbons were used in refrigerators.

Freons are non-toxic, non-flammable and easily liquefied, which made them nearly ideal refrigerants. They also destroy stratospheric ozone catalytically, and the Montreal Protocol of 1987 phased them out in favour of HFCs and hydrocarbons.

Answer: C

Clay is chiefly aluminium silicate.

Kaolinite, \(\mathrm{Al_2Si_2O_5(OH)_4}\), forms by the weathering of feldspar. Its layered sheet structure lets the plates slide over one another when wet, which is what makes clay plastic and mouldable.

Answer: A

Enzymes are proteins.

They are biological catalysts that lower the activation energy of a reaction, often by a factor of millions, and are highly specific to their substrate. A few RNA molecules also act catalytically - ribozymes - but the overwhelming majority of enzymes are proteins.

Answer: A

Carbon is present in every organic compound.

Organic chemistry is by definition the chemistry of carbon compounds. Carbon's ability to catenate - to bond to itself in chains and rings - and to form four strong covalent bonds is why its compounds outnumber those of all other elements combined.

Answer: B

Laughing gas is nitrous oxide, \(\mathrm{N_2O}\).

Humphry Davy named it for the euphoria it induces, and it is still used as a mild anaesthetic and analgesic mixed with oxygen. Nitric oxide, NO, and nitrogen dioxide, \(\mathrm{NO_2}\), are quite different and are toxic.

Answer: D

Phosphorus is kept under water to stop it catching fire in air.

White phosphorus ignites spontaneously at about 30 °C, close to room temperature in a warm climate. It is insoluble in water and denser than it, so a covering layer keeps oxygen away without dissolving or reacting with the element.

Answer: C

The two are separated by sublimation.

Iodine passes straight from solid to violet vapour on warming and recondenses as crystals on a cold surface, while potassium chloride, being non-volatile, stays behind. Filtration and sedimentation need one component to be insoluble in a liquid, and neither substance is a liquid to distil.

Answer: B

A catalyst hastens the attainment of equilibrium.

It provides an alternative path of lower activation energy, and it lowers that barrier equally for the forward and the reverse reaction. Both rates therefore rise by the same factor, so equilibrium is reached sooner but its position - the value of \(K\) - is unchanged.