Engineering Chemistry Questions and Answers – Hardness of Water

This set of Engineering Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Hardness of Water”.

1. Hardness of water is due to the presence of salts of ____________
a) Potassium
b) Chlorine
c) Magnesium
d) Boron
View Answer

Answer: c
Explanation: 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
View Answer

Answer: d
Explanation: 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
View Answer

Answer: b
Explanation: 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.
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4. Alkaline hardness is due to the presence of bicarbonate, carbonate and hydroxides of the hardness-producing metal ions.
a) True
b) False
View Answer

Answer: a
Explanation: 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
View Answer

Answer: d
Explanation: 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.
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6. Hardness of water is conventionally expressed in terms of equivalent amount of ____________
a) H2CO3
b) MgCO3
c) CaCO3
d) Na2 CO3
View Answer

Answer: c
Explanation: 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
View Answer

Answer: a
Explanation: The molar mass of MgSO4 is 120 and its n-factor is 2. So, chemical equivalent = Molar mass/ n-factor = 60.
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8. Which of the following is not a unit of hardness?
a) Parts per million
b) Degree centigrade
c) Degree clarke
d) Degree French
View Answer

Answer: b
Explanation: 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
View Answer

Answer: d
Explanation: 1 degree Clarke = 1 part of CaCO3 per 70,000 parts of water. It is calculated mathematically.
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10. 1 ppm = ____________
a) 0.07 0Fr
b) 0.70Fr
c) 0.10Fr
d) 0.010Fr
View Answer

Answer: c
Explanation: 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
View Answer

Answer: a
Explanation: 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
View Answer

Answer: b
Explanation: 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.

Sanfoundry Global Education & Learning Series – Engineering Chemistry.

To practice all areas of Engineering Chemistry, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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