Engineering Chemistry Multiple Choice Questions on “Hardness of Water”.
1. Hardness of water is due to the presence of salts of ____________
a) Potassium
b) Chlorine
c) Magnesium
d) Boron
Answer: c
Clarification: Hardness of water is due to the presence of salts of calcium and magnesium. Hard drinking water may have moderate health benefits, but can pose serious problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling towers, and other equipment that handles water.
2. Select the incorrect statement from the following option.
a) Water which does not form lather with soap and forms white scum is called hard water
b) Hard water contains dissolved calcium and magnesium salts in it
c) In hard water, cleansing quality of soap is depressed
d) Due to the presence of dissolved hardness-producing salts, the boiling point of water is depressed
Answer: d
Clarification: Due to the presence of dissolved hardness-producing salts, the boiling point of water is elevated. Elevation in boiling point is one of the most important colligative property. All the other options are correct.
3. Select the incorrect statement from the following option.
a) Permanent hardness is due to dissolved chlorides and sulphates of calcium and magnesium
b) It can be removed by mere boiling of water
c) It is also known as non-alkaline hardness
d) The difference between the total hardness and the alkaline hardness gives the non-alkaline hardness
Answer: b
Clarification: Unlike temporary hardness, permanent hardness is not destroyed on boiling. Varoius methods are adopted for the removal of permanent hardness like zeolites, lime-soda process etc. All the other options are correct.
4. Alkaline hardness is due to the presence of bicarbonate, carbonate and hydroxides of the hardness-producing metal ions.
a) True
b) False
Answer: a
Clarification: Alkaline hardness is due to the presence of bicarbonate, carbonate and hydroxides of the hardness-producing metal ions. This is also called carbonate hardness. It is temporary and can be removed easily by boiling.
5. Select the incorrect statement from the following option.
a) The taste of hard water is better than soft water
b) The dissolved calcium in hard water can help to produce strong teeth
c) Hard water coats the lead piping with a layer of insoluble calcium carbonate which prevents poisonous lead dissolving in water
d) Boiler feed water should also be hard in nature
Answer: d
Clarification: Boiler feed water should be free from hardness otherwise explosion may occur. All the other options are correct. The taste of hard water is better than soft water and dissolved calcium in hard water can help to produce strong teeth. Hard water coats the lead piping with a layer of insoluble calcium carbonate which prevents poisonous lead dissolving in water.
6. Hardness of water is conventionally expressed in terms of equivalent amount of ____________
a) H2CO3
b) MgCO3
c) CaCO3
d) Na2 CO3
Answer: c
Clarification: Hardness of water is conventionally expressed in terms of equivalent amount of CaCO3. The total water hardness is the sum of the molar concentrations of Ca2+ and Mg2+, in mol/L or mmol/L units.
7. The chemical equivalent of MgSO4 salt is ____________
a) 60
b) 47.5
c) 82
d) 68
Answer: a
Clarification: The molar mass of MgSO4 is 120 and its n-factor is 2. So, chemical equivalent = Molar mass/ n-factor = 60.
8. Which of the following is not a unit of hardness?
a) Parts per million
b) Degree centigrade
c) Degree clarke
d) Degree French
Answer: b
Clarification: Degree centigrade is not a unit of hardness. Degree centigrade is the unit of temperature. The unit for hardness is ppm (parts per million), degree clarke and degree french. All these three units are inter-related.
9. 1 degree Clarke = 1 part of CaCO3 per _____________ parts of water.
a) 10,000
b) 30,000
c) 50,000
d) 70,000
Answer: d
Clarification: 1 degree Clarke = 1 part of CaCO3 per 70,000 parts of water. It is calculated mathematically.
10. 1 ppm = ____________
a) 0.07 0Fr
b) 0.70Fr
c) 0.10Fr
d) 0.010Fr
Answer: c
Clarification: 1 ppm = 0.10Fr. It is calculated mathematically.
11. How many grams of MgCO3 dissolved per litre gives 84 ppm hardness?
a) 70.56 mg/L
b) 48.23 mg/L
c) 81.49mg/L
d) 66.12 mg/L
Answer: a
Clarification: 70.56 mg/L of MgCO3 dissolved per litre gives 84 ppm hardness.
12. EDTA method for hardness determination is a less accurate and inconvenient procedure.
a) True
b) False
Answer: b
Clarification: EDTA method for hardness determination is a more accurate, convenient and rapid procedure. Ethylene diaminetetraacetic acid (EDTA), is an amino poly-carboxylic acid and a colorless, water-soluble solid.