Chemistry Questions and Answers

Answer: D

Zymase converts glucose and fructose into alcohol.

\[\mathrm{C_6H_{12}O_6 \xrightarrow{zymase} 2\,C_2H_5OH + 2\,CO_2}\] It is a complex of enzymes secreted by yeast. Invertase acts earlier in the sequence, splitting sucrose into the two hexoses that zymase then ferments.

Answer: C

Poling removes reducible oxides from a metal.

Molten metal is stirred with green wooden poles; the wood gives off hydrocarbon gases that reduce the oxide back to the metal. It is used to refine copper containing cuprous oxide, and tin. Liquation separates by melting point, cupellation removes lead from silver, and electrorefining works by electrolysis.

Answer: D

Living in a large and well furnished house is not important for health.

Health depends on clean surroundings, adequate food and income, and social equality and harmony, which determine whether a person can actually obtain those things. The size or furnishing of a house adds comfort but not health.

Answer: D

Urea contains carbon, oxygen, nitrogen and hydrogen.

Its formula is \(\mathrm{NH_2CONH_2}\), or \(\mathrm{CO(NH_2)_2}\). Wöhler's synthesis of urea from ammonium cyanate in 1828 was the first preparation of an organic compound from an inorganic one, and ended the vital-force theory.

Answer: B

The atomic number is always a whole number.

It counts the protons in the nucleus, and one cannot have a fraction of a proton. Atomic mass is an average weighted over the natural isotopes and so is usually fractional, as with chlorine's 35.5, while radius and volume are measured quantities.

Answer: B

The answer is 0.2 mole of \(\mathrm{KMnO_4}\).

\[n(\mathrm{Ag})=\frac{21.6}{108}=0.2\ \text{mol}\]

so the sample contains \(0.2\,N_A\) atoms. The option that contains the same number of particles is the one holding 0.2 mole of molecules. For comparison, 1.8 g of \(\mathrm{H_2O}\) and 4.6 g of \(\mathrm{C_2H_5OH}\) are each 0.1 mole.

Answer: A

Brass tarnishes because of hydrogen sulphide in the air.

Traces of \(\mathrm{H_2S}\) react with the copper of the alloy to form a thin layer of black copper sulphide. The same gas is what blackens silverware.

Answer: D

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

There the air supply is plentiful, combustion is complete, and the flame reaches about 1,500 °C while burning pale blue. The luminous yellow zone is cooler because combustion is incomplete, its light coming from glowing carbon particles, and the innermost dark zone is unburnt gas.

Answer: A

An element is the simplest form of matter.

It cannot be broken down into anything simpler by chemical means, since it consists of atoms of one kind only. An atom is a particle rather than a form of matter, and molecules and compounds are built from elements.

Answer: D

Isotopes differ in the number of neutrons.

They have the same atomic number, so they are the same element with the same chemistry, but different mass numbers. Their atomic masses therefore differ too - but the neutron count is the underlying cause, not the effect.