Which of the properties of the element is a whole number
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.
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Trichloroacetaldehyde was subject to Cannizzaro's reaction by using NaOH. The mixture of the products contains sodium trichloroacetate andanother compound. The other compound is :
Answer: B
The other product is 2,2,2-trichloroethanol.
Chloral, \(\mathrm{CCl_3CHO}\), has no \(\alpha\)-hydrogen, so it undergoes the Cannizzaro reaction: \[\mathrm{2\,CCl_3CHO + NaOH \rightarrow CCl_3COONa + CCl_3CH_2OH}\] One molecule is oxidised to the salt of the acid and the other reduced to the primary alcohol. Chloroform would come from the haloform reaction, which is a different process.
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The substances that are composed of to or more different elements in fixed proportion by mass are called
Answer: B
Such a substance is a compound.
Its elements are chemically combined in a fixed ratio by mass - the law of constant proportions - and it has properties quite unlike those of its constituents. A mixture can be in any proportion and keeps the properties of its components.
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One method by which the components of air can be seperated is
Answer: C
The components of air are separated by fractional distillation of liquid air.
The air is freed of dust, moisture and carbon dioxide, then compressed and cooled until it liquefies, and the liquid is fractionated. Nitrogen boils off first at \(-196\) °C, then argon at \(-186\) °C and oxygen at \(-183\) °C.
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Ethylene glycol is used as an antifreeze in a cold climate. The mass of ethylene glycol that should be added to 4 kg of water to prevent it from freezing at −6°C will be: (Kf for water = 1.86 K kg mol−1, molar mass of ethylene glycol = 62 g mol−1)
Answer: C
The answer is 800 g.
Depression of freezing point: \[\Delta T_f = K_f\, m \Rightarrow m = \frac{\Delta T_f}{K_f} = \frac{6}{1.86} = 3.226\ \mathrm{mol\,kg^{-1}}\]
For 4 kg of water, \[n = 3.226 \times 4 = 12.90\ \text{mol}\]
\[w = n \times M = 12.90 \times 62 = 800\ \mathrm{g}\]
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Which of the following is a regenerated fibre?
Answer: B
Rayon is a regenerated fibre.
It is made from natural cellulose - wood pulp - which is dissolved and then extruded and re-solidified as filaments, so the polymer itself is natural but the fibre is man-made. Terylene and nylon are wholly synthetic, and silk is a natural protein fibre.
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A bond formed by sharing of electrons between atoms of the element is called
Answer: B
This is a covalent bond.
Two atoms share a pair of electrons, each contributing one, so that both attain a stable configuration - as in \(\mathrm{H_2}\), \(\mathrm{Cl_2}\) and \(\mathrm{CH_4}\). In a coordinate bond the shared pair comes from one atom only.
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The main element used in the vulcanisation of rubber is
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.
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'Minamata' disease was caused by ?
Answer: B
Minamata disease was caused by mercury.
A chemical plant discharged methylmercury into Minamata Bay in Japan from the 1930s; it accumulated in fish and shellfish, and those who ate them suffered severe neurological damage. The disease was formally identified in 1956.
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Which among the following is the most electronegative element?
Answer: A
Fluorine is the most electronegative element, at 4.0 on the Pauling scale.
Electronegativity increases across a period and decreases down a group, so fluorine - small, with a high effective nuclear charge and only one shell of shielding - sits at the maximum. Oxygen follows at 3.5, then chlorine at 3.0, bromine 2.8 and iodine 2.5.
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