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Hard Water and Soft Water - Practice Questions & MCQ
Edited By admin | Updated on Sep 18, 2023 18:35 AM | #JEE Main
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Hard and Soft Water is considered one of the most asked concept.
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42 Questions around this concept.
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The concentration of fluoride, lead, nitrate, and iron in a water sample from an underground lake was found to be 1 ppm, 40 ppm, 100 ppm, and 0.2 ppm, respectively. This water is unsuitable for drinking due to high concentration of :
The correct description of soft water's properties
While boiling water they form precipitates,what are those?
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Treatment with lime can remove hardness of water caused by
A. $\mathrm{CaCl}_2$
B. $\mathrm{CaSO}_4$
C. $\mathrm{Ca}\left(\mathrm{HCO}_3\right)_2$
D. $\mathrm{CaCO}_3$
Permanent hardness of water can be removed by
(A) Heating
(B) Treating with sodium acetate $\mathrm{CH}_3 \mathrm{CO}_2 \mathrm{Na}$
(C) Treating with $\mathrm{Ca}\left(\mathrm{HCO}_3\right)_2$
(D) Treatment with sodium hexametaphate $N a_6 P_6 O_{18}$
Given below are two statements :
Statement I: Permutit process is more efficient compared to the synthetic resin method for the softening of water.
Statement II: Synthetic resin method results in the formation of soluble sodium salts.
In the light of the above statements, choose the most appropriate answer from the options given below:
The precipitate that formed while removing permanent hardness of water
Which of the following is Haber's process?
Which of the following compounds is used for water softening?
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Hard and Soft Water
Water is said to be soft if it produces sufficient lather with the soap and water is described as being hard if it forms an insoluble scum before it forms lather with soap. The hardness of natural water is generally caused by the presence of the bicarbonates and sulphates of calcium and magnesium but in fact all soluble salts that form a scum with soap cause hardness.
Soap will not produce lather with water until all the calcium and magnesium ions have been precipitated. Hard water thus wastes soap. The hardness of water is of two types:
- Temporary hardness
- Permanent hardness
Softening of Water - Removing Temporary Hardness
Temporary hardness
Temporary hardness is due to the presence of magnesium and calcium hydrogen carbonates. It can be removed by:
- Boiling: During boiling, the soluble Mg(HCO3)2 is converted into insoluble Mg(OH)2 and Ca(HCO3)2 is changed to insoluble CaCO3.It is because of high solubility product of Mg(OH)2 as compared to that of MgCO3, that Mg(OH)2 is precipitated. These precipitates can be removed by filtration. Filtrate thus obtained will be soft water.
- Clark’s method: In this method calculated amount of lime is added to hard water. It precipitates out calcium carbonate and magnesium hydroxide which can be filtered off.
Removal of Permanent Hardness
Permanent hardness
It is due to the presence of soluble salts of magnesium and calcium in the form of chlorides and sulphates in water. Permanent hardness is not removed by boiling. It can be removed by the following methods:
- Washing soda: It removes both the temporary and permanent hardness by converting soluble calcium and magnesium compounds into insoluble carbonates.
- Permutit: Permutit is the technical name given to certain hydrated silicates of aluminium and sodium. It is obtained by fusing sodium carbonate, china clay, silica or quartz. The crystalline mass obtained is sodium alumino-silicate or sodium zeolite (Na2Al2Si2O8.xH2O) and is technically called as permutit. The sodium ions of permutit are exchanged with calcium and magnesium ions when hard water is passed through it thus removing the hardness of the water
These ions can be re-exchanged by treating it with brine(NaCl) solution.
This method is useful for the removal of both temporary and permanent hardness of water. - Calgon: The complex salt of metaphosphoric acid, sodium hexametaphosphate(NaPO3)6, is known as calgon. It is represented as Na2[Na4(PO3)6]. Calcium and magnesium salts present in hard water react with calgon to give complex salts.
- By ion exchange resins: Ion exhange resins are the most popular water softeners these days. These resins are synthetic substances. The cation exchanger consists of granular insoluble organic acid resin having giant molecules with -SO3H or -COOH groups while the anion exchanger contains giant organic molecules with basic groups derived from amines.
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