Softening MCQ Quiz in मल्याळम - Objective Question with Answer for Softening - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

Explanation:

Zero Hardness of Water

• Water hardness is primarily caused by dissolved calcium and magnesium ions.

• These ions can interfere with soap usage and cause scaling in pipes and boilers.

• To achieve zero hardness, all calcium and magnesium ions must be removed from the water.

• The zeolite process is a highly effective method for achieving zero hardness.

• In this process, hard water is passed through a zeolite bed, which exchanges sodium ions for calcium and magnesium ions.

• The sodium ions do not contribute to water hardness, thus resulting in softened water.

• The lime-soda process and excess lime treatment can reduce water hardness but cannot achieve zero hardness.

• Excess alum and lime treatment is used for coagulation and sedimentation, not for complete removal of hardness.

• Therefore, option 3 (zeolite process) is the correct answer to achieve zero hardness of water.

Explanation:

Temporary Hardness of Water – Cause and Details

• Temporary hardness in water is primarily caused by the presence of bicarbonates of calcium and magnesium.

• These bicarbonates decompose upon heating, forming insoluble carbonate precipitates and removing hardness from water.

• The decomposition reaction involves the conversion of bicarbonates into carbonates, water, and carbon dioxide gas.

• This type of hardness is referred to as "temporary" because it can be easily removed by boiling the water.

• The substances that contribute to temporary hardness are calcium bicarbonate (Ca(HCO3)2) and magnesium bicarbonate (Mg(HCO3)2).

• Other salts, such as chlorides, nitrates, and sulphates, do not cause temporary hardness.

• These substances are responsible for permanent hardness, which cannot be removed by boiling.

• Temporary hardness is therefore distinct from permanent hardness, making its removal relatively straightforward.

• In conclusion, temporary hardness is caused by carbonates (bicarbonates specifically), which is why the correct answer is Option 2.

Explanation:

Hardness of water:

Hardness in water is that characteristic which prevents the formation of sufficient leather or foam, when such hard waters are mixed with soap. It is usually caused by the presence of calcium and magnesium salts present in water, which form scum by reaction with soap.

Water softening:

The process of removal of hardness from water is known as Water softening

Removal of hardness;

1. Temporary hardness

The temporary or carbonate hardness, which is caused by carbonates ad bicarbonates of Ca and Mg or bivalent cations.

The methods of removing temporary hardness

1. Boiling  
2. Addition of  lime.

2. Permanent hardness

The permanent or non carbonate hardness, which is caused by the sulphates, chlorides and nitrates of Ca and Mg are removed by special methods.

The methods of removing permanent hardness

• Lime soda process
• Base exchange process
• Demineralization​​​.​​​

Explanation

The flowchart for the whole distribution system is shown in the figure below-

Since there are four households in total with a requirement of 500 ltr per house per day, 

the total discharge = 4 × 500 ltr per house per day = 2000 ltr per day

Given, the hardness at the source = 500 mg/l
the hardness to be maintained while supplying to the household = 75 mg/l

Assume a discharge of Q1 ltr per day passes through the hardness removal system and rest through the bypass,

As the water passes through the hardness removal system, the hardness will become aero as efficiency is 100 percent.

 then the hardness concentration at the household:

Final hardness concentration \(= \frac{{{Q_1} \;\times \;0\; + \;{Q_2}\; \times \;500}}{Q} = \frac{{{Q_1}\; \times \;0\; +\; (Q \;- \;{Q_1})\; \times \;500}}{Q} = 75\)

⇒ Putting Q = 2000 ltr/d, (2000 – Q1) × 500

= 2000 × 75

⇒ Q1 = 1700 ltr/day

⇒ Q2 = Discharge passing through the bypass

= 2000 – 1700

= 300 ltr/day

= 300/24

= 12.5 ltr/hr

∴ Options 3) and 4) are correct.