Chemistry Questions and Answers

Answer: B

Zymase converts glucose to ethyl alcohol.

Secreted by yeast, it catalyses \[\mathrm{C_6H_{12}O_6 \rightarrow 2\,C_2H_5OH + 2\,CO_2}\] Invertase first splits sucrose into glucose and fructose, diastase converts starch to maltose, and maltase maltose to glucose - zymase completes the chain.

Answer: C

These are isotones.

They share the neutron number but differ in protons, so both the element and the mass number differ - \(^{14}_{6}\mathrm{C}\), \(^{15}_{7}\mathrm{N}\) and \(^{16}_{8}\mathrm{O}\) each have 8 neutrons.

Answer: C

Glenn T. Seaborg is credited with the discovery of the transuranic elements.

With his co-workers at Berkeley he identified plutonium, americium, curium, berkelium and californium among others, and shared the 1951 Nobel Prize for the work. Element 106, seaborgium, is named after him - the only element named for a living person at the time.

Answer: B

Dust is removed by electrophoresis, in the Cottrell precipitator.

Smoke is a colloidal sol of solid particles carrying an electric charge. Passing the flue gas between electrodes at a high potential difference discharges the particles, so they lose their mutual repulsion, coagulate and fall - and only the clean gas leaves the chimney.

Answer: B

The answer is 3.05 g.

The reaction is \[\mathrm{P_4 + 5\,O_2 \rightarrow P_4O_{10}}\]

Moles of each reactant: \[n(\mathrm{P_4})=\frac{1.33}{124}=0.01073\ \text{mol},\qquad n(\mathrm{O_2})=\frac{5.07}{32}=0.1584\ \text{mol}\]

\(0.01073\) mol of \(\mathrm{P_4}\) needs \(5\times0.01073=0.0536\) mol of \(\mathrm{O_2}\), and far more is available, so \(\mathrm{P_4}\) is the limiting reagent.

One mole of \(\mathrm{P_4}\) gives one mole of \(\mathrm{P_4O_{10}}\) \((M=284\ \mathrm{g\,mol^{-1}})\): \[m=0.01073\times284=3.05\ \mathrm{g}\]

Answer: B

Blood is a natural colloid.

It is a sol in which albumin and other proteins, and the cells themselves, are dispersed in plasma. The particles are large enough to scatter light (the Tyndall effect) but too small to settle out. Sugar, salt and urea solutions are true solutions with particles of molecular size.

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: 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: D

Antimony is a metalloid.

It lies along the staircase separating metals from non-metals in the periodic table and shows properties of both: it has a metallic lustre and forms alloys, yet it is brittle and a poor conductor. Boron, silicon, germanium, arsenic and tellurium are the others.

Answer: A

Natural rubber is derived from isoprene, 2-methyl-1,3-butadiene.

The latex tapped from Hevea brasiliensis contains cis-1,4-polyisoprene. The cis geometry keeps the chains from packing closely, which is what makes the material elastic.