(b)
(i) State a reason for each of the following:
I. The lid of a desiccator should be made air-tight by greasing.
II. The milkiness of lime water disappears when excess carbon (IV) oxide is passed into it.
(ii) Write a chemical equation for (b)(i) II.
(iii) Name two gases that can be used for the fountain experiment.
Answer (1)
This question pertains to some fundamental concepts in chemistry regarding reactions and gas properties.
(b)(i) State a reason for each of the following:
I. The lid of a desiccator should be made air-tight by greasing.
A desiccator is used to keep moisture-sensitive chemicals dry. The purpose of greasing the lid is to ensure an air-tight seal, preventing moisture from the air from entering the desiccator. This maintains a dry environment inside, which is crucial for storing hygroscopic (moisture-absorbing) substances.
II. The milkiness of lime water disappears when excess carbon (IV) oxide is passed into it.
When carbon dioxide ( CO 2 ) is bubbled into lime water ( Ca(OH) 2 ),) a white precipitate of calcium carbonate ( CaCO 3 ) forms, giving the solution its milky appearance.
However, if excess carbon dioxide is passed through, the calcium carbonate reacts further to form calcium bicarbonate ( Ca(HCO 3 ) 2 ),) which is soluble in water, causing the milkiness to disappear.
(ii) Write a chemical equation for (b)(i) II.
The chemical reactions involved are:
Initial reaction causing milkiness: Ca(OH) 2 ( aq ) + CO 2 ( g ) → CaCO 3 ( s ) + H 2 O ( l )
Further reaction with excess carbon dioxide: CaCO 3 ( s ) + CO 2 ( g ) + H 2 O ( l ) → Ca(HCO 3 ) 2 ( aq )
(iii) Name two gases that can be used for the fountain experiment.
The fountain experiment usually demonstrates the solubility of gases in water by showing a pressure difference. Two gases commonly used in this experiment are:
Ammonia ( NH 3 )
Hydrogen chloride ( HCl )
These gases demonstrate strong solubility in water, creating a pressure difference that draws liquid up into the inverted flask, forming a fountain.
