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Basic Environmental Engineering Questions on “Chemical Characteristic of Water”.
1. Chlorides are estimated by titration with a standard silver nitrate solution by using _______ as an indicator.
a) Potassium manganate
b) Potassium chloride
c) Potassium chromate
d) Potassium dichromate
Answer: c
Clarification: 2-3 drops of potassium chromate are added to appropriate amount of water sample and then it is titrated with a standard solution of silver nitrate.
2. Carbonate hardness can be removed by adding lime to water.
a) True
b) False
Answer: a
Clarification: Carbonate hardness is due to the presence of carbonates and bicarbonates of calcium and magnesium in water and can be removed by boiling or by adding lime to it.
3. Which of the following statement is wrong regarding permanent hardness?
a) It is also called carbonate hardness
b) It is due to the presence of sulfates, chlorides and nitrates of calcium and magnesium
c) It cannot be removed by boiling
d) It requires special methods of water softening to get removed
Answer: a
Clarification: Permanent hardness is called non-carbonate hardness whereas temporary hardness is called carbonate hardness.
4. One degree of hardness is equivalent to ___ ppm.
a) 2
b) 1
c) 10
d) 100
Answer: b
Clarification: Water is said to have one degree of hardness when its soap destroying power is equivalent to the effect of 14.25mg of calcium carbonate in one litre of water.
5. What can be filled in place of the question mark in the following table?
| Degree of hardness | Nature of water |
|---|---|
| 1 | Extremely soft water |
| 2 | Very soft water |
| 3 | Soft water |
| 9 | ? |
a) Excessive hard water
b) Reasonably soft water
c) Very hard water
d) Hard water
Answer: d
Clarification: When the degree of hardness is 9, then it indicates the hard water. For excessive hard water, it is 15 and for very hard water, it is 11.
6. In which method of determining total hardness of water is based on the premise that hardness producing substance react with soap and form insoluble compounds before lather is produced?
a) Clark’s method
b) Hehner’s method
c) Versenate method
d) EDTA method
Answer: a
Clarification: In Clark’s method, total hardness is found by determining the standard soap solution required to obtain permanent lather with the water sample of known volume.
7. What is the indicator used in EDTA method?
a) Potassium chromate
b) Potassium dichromate
c) Potassium chloride
d) Erio chrome, black T
Answer: d
Clarification: Hardness is determined by using Ethylene diamine tetra-acetic acid using Erio chrome, black T as indicator at a pH between 8.5 and 11.
8. The permissible limit of pH preferred for potable water is ___ ppm.
a) 6.5-9
b) 7-8.5
c) 10-14
d) 0-7
Answer: a
Clarification: The permissible limit of pH for potable water should not exceed 9 and should not be less than 6.5 and the preferred limit is 7-8.5.
9. Given list 1 and list 2, find which of the following pair is correctly matched?
| List 1 (Chemical substance) | List 2 (Permissible limit in ppm) |
|---|---|
| A. Lead | 1. 0.05 |
| B. Phenol | 2. 0.001 |
| C. Zinc | 3. 0.01 |
| D. Chromium | 4. 5 |
| 5. 0.2 |
a) A-5
b) B-3
c) C-4
d) D-2
Answer: c
Clarification: Lead has a permissible limit of 0.05ppm, phenol has 0.001ppm, zinc has 5ppm and chromium has a permissible limit of 0.05ppm in water.
10. What is the concentration of H+ ions in moles/L in water if the pOH value is 6?
a) 10-6
b) 10-7
c) 10-8
d) 10-9
Answer: c
Clarification: pH + pOH = 14
pOH = 6, so pH = 14-6 = 8
H+ = 10-pH = 10-8moles/L.
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