I: Concentrated sulphuric acid

Here are the solutions to questions 3 and 4:

3 (a)
I: Concentrated sulphuric acid
II: Concentrated sulphuric acid
III: Water
IV: Beaker

3 (b)
It is important to dilute concentrated sulphuric acid by adding it slowly to water because the dilution process is highly exothermic, releasing a large amount of heat. Adding acid to water allows the heat to dissipate gradually, preventing the water from boiling violently and splashing the corrosive acid. If water were added to concentrated acid, the less dense water would float on top, boil rapidly, and cause the acid to splatter dangerously.

3 (c)
Two precautions that must be taken are:

• Always add acid to water, never water to acid: This ensures that the more dense acid is added slowly to the larger volume of water, allowing heat to dissipate safely.
• Stir the mixture continuously: Stirring helps to distribute the heat evenly throughout the solution and prevents localized overheating.
• Wear safety goggles: To protect the eyes from potential splashes of corrosive acid.
• Use a heat-resistant container: To prevent the container from cracking due to the heat generated.

3 (d)
Two protective devices that can be used are:

• Safety goggles
• Lab coat

3 (e)
The diluted solution can be confirmed as an acid by:

• Using blue litmus paper: It will turn red.
• Using a pH meter or pH paper: It will show a pH value less than 7.
• Adding a carbonate (e.g., calcium carbonate): It will produce effervescence (fizzing) due to the release of carbon dioxide gas.

4 (i)

a) The man is suffering from myopia (short-sightedness).

b) The defect is caused by the eyeball being too long or the cornea/lens having too much converging power, causing light rays to focus in front of the retina.

c) A concave lens (diverging lens) would be needed to correct the defect.

4 (ii)

a)
$\alpha$: Stopper (or Cork)
$\beta$: Vacuum
$\gamma$: Silvered surface

b) Heat lost by conduction is prevented by the vacuum between the walls and the poorly conducting stopper.

c) Heat lost by convection is prevented by the vacuum between the walls, which eliminates air movement, and the stopper, which prevents air from entering or leaving.

d) Heat lost by radiation is prevented by the silvered surfaces on the inner and outer walls, which reflect infrared radiation.