Environmental Engineering Multiple Choice Questions on “Chlorination”.
1. Which of the following is termed as free available chlorine?
a) Hypochlorous acid
b) Hypochlorite ions
c) Molecular chlorine
d) Hypochlorous acid, Hypochlorite ions, Molecular chlorine
Answer: d
Clarification: The chlorine existing in water as hypochlorous acid, hypochlorite ions, molecular chlorine is termed as free available chlorine.
2. At what pH, chlorine exists as molecular chlorine?
a) 3
b) 5
c) <5
d) <10
Answer: c
Clarification: When chlorine is added to water, the chlorine acts as molecular chlorine only when its pH is less than 5.
3. When the pH is between 5 and 10, the chlorine in the water acts as ______
a) Hypochlorous acid
b) Hypochlorite ions
c) Molecular chlorine
d) Hypochlorous acid hypochlorite ions
Answer: d
Clarification: When the pH is between 5 and 10, the chlorine in the water acts as hypochlorous acid and hypochlorite ions. As pH increases, the concentration of hypochlorous acid decreases while of hypochlorite ions increases.
4. At what pH, chlorine in water acts as only hypochlorite ions?
a) <5
b) >5
c) >10
d) <3
Answer: c
Clarification: HOCl <——> H+ + HOCl–
Where, HOCl is hypochlorous acid and HOCl– is hypochlorite ions.
At pH<10, only HOCl– is produced.
5. The hypochlorous acid is ______ times effective as hypochorite ions.
a) 10
b) 30
c) 50
d) 80
Answer:d
Clarification: The hypochlorous acid is 80 times more effective as hypochorite ions, so the pH of water to be treated should be less than 7 to prevent the ionization of it.
6. Chlorine which gets consumed in the oxidation of impurities before disinfection is ______________
a) Free chlorine
b) Residual chlorine
c) Chlorine demand
d) Residual demand
Answer: c
Clarification: Chlorine has the oxidizing power which oxidizes organic and inorganic impurities present in water and the amount of chlorine, which gets consumed before disinfection is called as chlorine demand.
7. The chlorine, which serves as a disinfectant is ___________
a) Free chlorine
b) Free Residual chlorine
c) Chlorine demand
d) Residual demand
Answer: b
Clarification: When chlorine demand is fulfilled, then chlorine is available s free residual chlorine, which contains hypochlorous acid and hypochlorite ions.
8. The permissible limit of free residual chlorine is ___________
a) 0.02ppm
b) 0.2ppm
c) 1ppm
d) 2ppm
Answer: b
Clarification: The water is satisfactorily disinfected if the free residual chlorine is 0.2 ppm at the contact period of 10 minutes.
9. What is the chemical formula of bleaching powder?
a) Ca (OCl)2
b) Ca (OCl)
c) Ca (OCl)3
d) CaCl2
Answer: a
Clarification: The chemical formula of bleaching powder is Ca (OCl)2. It is called as chlorinated lime.
10. Bleaching powder contains ______ of available chlorine.
a) 16%
b) 33.3%
c) 66.6%
d) 99.9%
Answer: b
Clarification: Bleaching powder contains 33.3% of available chlorine. It loses its strength during storage and therefore, it is used during emergency conditions.
11. The process of chlorination with hypochlorites is called ___________
a) Super chlorination
b) Pre chlorination
c) Post chlorination
d) Hypo-chlorination
Answer: d
Clarification: The process of chlorination with hypochlorites is called Hypo-chlorination.
Hypochlorites are applied to water as a solution by the hypochlorite feeding apparatus.
12. Normally, the ratio of ammonia and chlorine in chloramine is?
a) 1:1
b) 1:2
c) 1:4.5
d) 1:3.5
Answer: c
Clarification: Normally, the ratio of ammonia and chlorine in chloramine is 1:4.5. They are more effective than chlorine.
13. Which type of chloramine is formed when pH of water is 4.4?
a) Monachloramine
b) Dichloramine
c) Trichloramine
d) Both monochloramine and dichloramine
Answer: b
Clarification: When the pH<4.4, then trichloramine is formed and when pH lies in the range 4.4-5, then only dichloramine is formed.
14. What is the contact period for disinfection with chloramine?
a) 1hour
b) 2hours
c) 3hours
d) 4hours
Answer: b
Clarification: The disinfecting reaction with chloramine are slower than with chlorine alone, so the contact period of 2 hours is provided.