Question

14. Sometimes chlorine gas is passed
through water for its purification,
What will be the pH value of such
a sample of water?
A. Equal to 7
B. More than 7
C. Less than 7
D. Very near to 8​

Answer 1

Answer:

it's between 6.5. to 8.5

Answer 2

Answer:

The pH value of the water is less than 7 after chlorine gas is passed through it. (Option C)

Explanation:

Chlorine(Cl₂) is heavier than air, toxic, and economically available oxidizing agent, and non-flammable.

• Can be used as a disinfectant.
• It is available in three forms: sodium hypochlorite, calcium hypochlorite, and liquid chlorine.

Sodium hypochlorite is also called liquid bleach.

• Its strength is 15%  by its weight.
• It can be added to down flowing stream with the help of a chemical metering pump or even by physical dumping.

Calcium hypochlorite, It is powder chlorine.

• It is 70% of the available chlorine.
• This can be added to the down flow of water with the help of pellets or even by mixing a solution of calcium hypochlorite and water.
• This solution is discharged into a tank with the help of small chemical feed pump.  

Liquid Chlorine also known as chlorine gas.

• Chlorine is in its elemental form.
• It is a compressed gas of 100% strength.
• It is introduced to the water with a vacuum-operated solution feed system.

All three produce hypochlorous acid, which is the oxidizing agent.

When the chlorine gas is mixed in water, it reacts to form hypochlorous acid and hydrochloric acid.

Cl₂+H₂O = HOCl + HCl.

If the pH of the water is less than 6.5, there won't be dissociation. if the pH is above 8.5, then there is complete dissociation of chlorine and hypochlorite ions will dominate.  

If the pH is between 6.5 and 8.5, it consists of both hypochlorous acid and hypochlorite.

Hence, when chlorine gas is passed through the water its pH is less than 7, (Option C).