Chemistry Questions and Answers

Answer: C

Silver does not give hydrogen with dilute hydrochloric acid.

Only metals above hydrogen in the reactivity series displace it from an acid. Zinc, iron and calcium all lie above hydrogen and react; silver lies below it, so it is unattacked by dilute HCl and dissolves only in oxidising acids such as nitric acid.

Answer: A

This is an ionic bond, also called an electrovalent bond.

One atom loses electrons and the other gains them, and the resulting oppositely charged ions are held by electrostatic attraction - as in \(\mathrm{Na^+Cl^-}\). It forms when the electronegativity difference is large, typically above about 1.7.

Answer: D

The M.K.S. system was introduced by Giovanni Giorgi in 1901.

He proposed building the system on the metre, kilogram and second and adding a fourth electrical unit, so that mechanical and electrical units would form one coherent set. That proposal is the direct ancestor of the SI adopted in 1960.

Answer: C

This is positional isomerism.

Both \(\mathrm{CH_3CHCl_2}\) and \(\mathrm{CH_2Cl\text{-}CH_2Cl}\) are \(\mathrm{C_2H_4Cl_2}\) with the same carbon chain and the same functional group; only the positions of the two chlorine atoms differ - both on one carbon, or one on each.

Answer: B

2-hydroxypropane can be oxidised to a carbonyl compound.

Propan-2-ol is a secondary alcohol and has a hydrogen on the carbon bearing the \(\mathrm{-OH}\), so it oxidises to the ketone acetone: \[\mathrm{CH_3CH(OH)CH_3 \xrightarrow{[O]} CH_3COCH_3}\] 2-methyl-2-hydroxypropane is tertiary, with no such hydrogen, and phenols cannot give a carbonyl without destroying the ring.

Answer: C

Long chains of repeating carbon-based units are polymers.

They are built from small molecules called monomers - ethylene giving polythene, and amino acids giving proteins. Hydrocarbons are simply compounds of carbon and hydrogen, of any length, and need not be chains of repeating units.

Answer: C

Sulphur is used to vulcanise rubber.

Charles Goodyear's process, heating raw rubber with 3–5 per cent sulphur at about 145 °C, forms sulphur cross-links between the polyisoprene chains. The chains can then no longer slide past one another, so the rubber becomes harder, more elastic and much less sensitive to temperature.

Answer: A

The atomic weight, or mass number, is the sum of the neutrons and protons.

These two together are the nucleons and carry almost all the mass of the atom. An electron weighs about 1/1836 of a proton, so electrons contribute nothing appreciable to the mass.

Answer: D

The hydronium ion is \(\mathrm{H_3O^+}\).

A bare proton is far too small and charge-dense to exist free in water, so it attaches to the lone pair of a water molecule: \[\mathrm{H^+ + H_2O \rightarrow H_3O^+}\] When we write \(\mathrm{H^+}\) in aqueous chemistry, this is what is meant.

Answer: B

Tetraethyl lead was used as a gasoline additive.

It is an anti-knock agent: it decomposes in the cylinder to lead and ethyl radicals which interrupt the chain reaction causing pre-ignition, raising the fuel's effective octane number. It has been phased out worldwide because lead is neurotoxic and poisons catalytic converters.