Question

3.
Sodium chloride obtained from sea water or from lakes contains many impurities such as sulphates of sodium and magnesium along with chlorides of calcium and magnesium. The chlorides of calcium and magnesium are particularly undesirable on account of their deliquescent nature.
For its purification, common salt is dissolved in minimum quantity of water to get a saturated solution from which insoluble impurities are filtered off. Then hydrogen chloride gas is passed through the saturated solution and the crystals of pure NaCl separate out. The soluble impurities remain in the mother liquor. The crystals are filtered, washed and dried.
(i) Select the correct statement regarding salt NaCl.
(a) Pure NaCI is hygroscopic in nature
(b) It is soluble in alcohol
(c) Pure NaCI is not hygroscopic, it shows hygroscopic nature due to impurities
(d) It is a brown crystalline solid
(ii) Nature of aqueous solution of common salt is
(a) acidic (b) alkaline (c) basic (d) neutral
(iii) In the given series of reactions, Y and Z respectively are
2
(a) NaHCO3 , NaOCl2 (b) NH4CI, Na2CO3 (c) Na2CO3 , NH4CI (d) Na2CO3, NaHCO3
(iv) Which of the following compounds is alkaline in aqueous medium?
(a) Na2CO3 (b) NaCI (c) H2CO3 (d) CuSO4
(v) Some statements regarding salt NaCI are given below
(I) It is prepared by chlor-alkali process
(II) It is a white crystalline substance
(III) It also exists in the form of rocks and is called rock salt
(IV) It is a neutral salt, pH value of NaCI is 7
(a) II and III only (b) III and IV only (c) I and IV only (d) II, III and IV only

Answer 1

The answers to the given questions are as follows:

(i). The correct answer is an option (c).

• NaCl or sodium chloride in its pure form is not hygroscopic in nature.
• It turns hygroscopic or starts absorbing moisture from the atmosphere when it has impurities present in it in the form of sulfate salts and chloride salts.

(ii). The correct answer is an option (d).

• Common salt, Nacl is the product of the neutralization reaction of acid and base.
• It does not hydrolyze further and therefore the nature of its aqueous solution has neutral pH of 7.

(iii). The correct answer is an option (b).

• When Sodium chloride reacts with ammonia, water, and carbon dioxide, the product obtained is sodium bicarbonate (X) and ammonium chloride (product Y) which on further heating gives sodium carbonate (product Z).

(iv). The correct answer is an option (a).

• The alkalinity or the basicity of the compounds depends on their tendency to produce OH⁻ ions (hydroxide ions) in water or an aqueous medium.
• Sodium carbonate in an aqueous medium dissociates hydroxide ions.

(v). The correct answer is an option (d).

The statements which are correct about NaCl are:

• It is a colorless to a white crystalline substance
• It exists in the form of rocks and is called rock salt
• It is a neutral salt, having a pH value of 7
• It is not prepared by the Chlor-alkali process therefore statement (I) is incorrect.