ICSE Class 10 Chemistry · Competency Practice · 7 solved questions
Calcium hydroxide solution is used to detect the presence of carbon dioxide gas, while sodium hydroxide is NOT. Justify.
Calcium hydroxide, when reacted with CO2 gives visible white precipitate of CaCO3. This verifies the test for CO2. However, sodium hydroxide does not give a visible change when reacted with CO2. This reaction forms sodium carbonate, which remains dissolved in solution. So, sodium hydroxide cannot be used to detect CO2 reliably.
Hydrogen chloride fumes in the air. Justify.
Hydrogen chloride gas fumes in air because it is highly soluble in the moisture (water vapour) present in air. It dissolves rapidly to form tiny droplets of hydrochloric acid, which appear as dense white fumes.
HCl (gas) + H2O (g) ⟶ HCl (aqueous)
During the extraction of aluminium bauxite, its principal ore is reduced by the electrolytic method. Why?
Alumina (Al2O3) in bauxite is a very stable oxide because aluminium has a strong affinity for oxygen making the bond between aluminum and oxygen very strong. Hence, it cannot be reduced by common reducing agents like carbon, carbon monoxide or hydrogen. Therefore, aluminium is extracted by electrolytic reduction.
Why is pure acetic acid also called glacial acetic acid?
The anhydrous acetic acid or 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.
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.
No. Tin is used because it lowers the melting point of the lead–tin alloy, so the fuse melts quickly when excess current flows and breaks the circuit. Copper has a much higher melting point, so a lead–copper alloy would not melt easily and would not act as an effective fuse.
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.
A coloured dye is added to ethyl alcohol to denature it so as to prevent the misuse (consumption) of alcohol.
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.
Element C will be at the top of group because it has the highest ionisation energy, and ionisation energy decreases down the group.
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