Chemistry Questions and Answers

Answer: D

Aspirin is acetylsalicylic acid.

It is made by acetylating salicylic acid with acetic anhydride, and works by irreversibly inhibiting the cyclo-oxygenase enzymes, so cutting the production of prostaglandins that cause pain, fever and inflammation. Methyl salicylate is oil of wintergreen.

Answer: B

This is the thermal capacity, or heat capacity, of the body.

\[C=\frac{Q}{\Delta T}\] measured in \(\mathrm{J\,K^{-1}}\). It depends on the mass of the particular body. Specific heat is the heat needed per unit mass for the same rise, and is a property of the substance rather than of the object.

Answer: C

Cadmium does not liberate hydrogen from water.

Sodium, lithium and potassium are all alkali metals, high in the reactivity series, and react with even cold water. Cadmium lies below hydrogen in the series and is unaffected by water at ordinary temperatures.

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: C

One-eighth of the isotope remains.

\[\text{number of half-lives} = \frac{6\ \mathrm{h}}{2\ \mathrm{h}} = 3\]

\[\frac{N}{N_0} = \left(\frac{1}{2}\right)^{3} = \frac{1}{8}\]

The quantity halves at 2 h, quarters at 4 h and falls to an eighth at 6 h.

Answer: C

The pH of pure water is 7 at 25 °C.

Water self-ionises to the extent that \[[\mathrm{H^+}] = [\mathrm{OH^-}] = 10^{-7}\ \mathrm{mol\,L^{-1}}\] so \(\mathrm{pH} = -\log(10^{-7}) = 7\). The value drifts below 7 at higher temperatures, but the water stays neutral because the two concentrations remain equal.

Answer: C

Formaldehyde is used to preserve specimens.

Formalin, a 40 per cent aqueous solution, cross-links the amino groups of proteins and so hardens the tissue and kills any bacteria or fungi that would decompose it. Its own pungency and toxicity are the drawback.

Answer: A

PVC stands for polyvinyl chloride.

It is the addition polymer of vinyl chloride, \(\mathrm{CH_2{=}CHCl}\). Rigid PVC is used for pipes and window frames; adding a plasticiser makes it flexible enough for cable insulation and flooring.

Answer: D

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

Where the air supply is plentiful, combustion is complete and the flame burns pale blue at about 1,500 °C. The luminous yellow zone owes its light to glowing unburnt carbon particles and is cooler, because combustion there is incomplete; the dark inner zone is unburnt gas and coldest of all.

Answer: C

John Dalton proposed the first atomic theory, in 1808.

His postulates were that matter consists of indivisible atoms, that all atoms of an element are alike in mass and properties, and that compounds form when atoms combine in fixed small whole-number ratios. The theory accounted at once for the laws of conservation of mass and of definite and multiple proportions.