ICSE Chemistry Competency Focused Practice Questions Solution- Very Short Answer Questions

ICSE Chemistry Competency Focused Practice Questions Solution-

VII. Very Short Answer Questions

Question 84. [Analytical Chemistry]
Calcium hydroxide solution is used to detect the presence of carbon dioxide gas, while
sodium hydroxide is NOT. Justify.

Answer:

Carbon dioxide gas reacts with calcium hydroxide to form a white precipitate of calcium carbonate. In reaction with sodium hydroxide, the product formed is sodium carbonate which is soluble in water.

Question 85. [Study of Compounds]
Hydrogen chloride fumes in the air. Justify.

Answer:

Hydrogen chloride is highly soluble even in the minute traces of moisture present in the
air. It forms a mist of droplets of hydrochloric acid which appears as white fumes.

Question 86. [Metallurgy]
During the extraction of aluminium bauxite, its principal ore is reduced by the
electrolytic method. Why?

Answer:

Aluminium is a very active metal, therefore the bond between aluminum and oxygen in Bauxite (Al₂O₃) is very strong. It cannot be reduced by common reducing agents like carbon, carbon monoxide or
hydrogen. In fact, any metal in the activity series above carbon is extracted by the method of electrolysis.

Question 87. [Organic Chemistry]
Why is pure acetic acid also called glacial acetic acid?

Answer:

Pure acetic acid, on cooling below 16.5°C, crystallises out to form a crystalline mass resembling ice. Hence it is called glacial acetic acid.

Question 88. [Metallurgy]
A fuse wire is an alloy made of tin and lead. It is a safety device that prevents the damage
of electronic gadgets due to excessive flow of current. Can copper replace tin when
making alloys? Justify your answer.

Answer:

No, because the melting point of copper is very high due to which it will not melt easily during short circuit. A fuse wire is an alloy made of tin and lead because it has high resistance and low melting point, so that it melts easily.

Question 89. [Organic Chemistry]
Ethyl alcohol is a colourless liquid. It is used as a major constituent in alcoholic
beverages and also in the manufacture of many chemicals. When a Chemical
Manufacturing Unit ordered ethyl alcohol, they were supplied with a purple-coloured
alcohol instead of a colourless one.
State the reason and the purpose of this colour change.

Answer:

A coloured dye is added to ethyl alcohol to denature it so as to prevent the misuse
(consumption) of alcohol.

Question 90. [Periodic Properties and Variations of Properties]
Ionisation energies of 4 elements A, B, C and D are 496, 403, 520 and 419 KJ/mol,
respectively. If these elements belong to the same group in the Periodic Table, which
element will occupy the top position in the group? Justify your answer.

Answer:

Element C will top the group because ionisation energy decreases down the group. The elements in decreasing order from top to bottom of the group will be C > A > D > B.