Chemistry Questions and Answers

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.

Answer: D

Aluminium is extracted from bauxite.

The ore is hydrated aluminium oxide with iron and silica impurities; the Bayer process purifies it to alumina, and the Hall–Héroult cell then reduces the alumina electrolytically in molten cryolite.

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

Petroleum is found in sedimentary rocks.

It forms from marine organic matter buried in fine-grained sediments and cooked over millions of years, then migrates upward through porous rock until an impermeable cap traps it. Igneous and metamorphic rocks form at temperatures that would destroy the hydrocarbons.

Answer: A

Nucleons are protons and neutrons.

They are the particles that make up the nucleus, and their total is the mass number. Electrons lie outside the nucleus and are not nucleons.