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Some Basic Concepts of Chemistry question

2015 · Shift 0 · Q4
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Some Basic Concepts of Chemistry question

2015 · Shift 0 · Q4

JEE MainChemistrySome Basic Concepts of ChemistryMCQ+4 / −1
The molecular formula of a commercial resin used for exchanging ions in water softening is C8H7SO3NaC_8H_7SO_3NaC8​H7​SO3​Na (Mol. Wt. 206). What would be the maximum uptake of Ca2+Ca^{2+}Ca2+ ions by the resin when expressed in mole per gram resin?
  1. A
    2/309
  2. B
    1/412
  3. C
    1/103
  4. D
    1/206
View written solutionFree

Correct answer: B

  1. Identify the exchangeable ion in the resin

The resin has formula: C8H7SO3NaC_8H_7SO_3NaC8​H7​SO3​Na with molar mass 206206206 g mol−1^{-1}−1.

This is a sodium salt resin, so each formula unit contains one exchangeable Na+Na^+Na+ ion.

  1. Ion-exchange stoichiometry with calcium ions

Since calcium is divalent, the exchange process is: 2R−SO3−Na++Ca2+→(R−SO3−)2Ca+2Na+2R{-}SO_3^-Na^+ + Ca^{2+} \rightarrow (R{-}SO_3^-)_{2}Ca + 2Na^+2R−SO3−​Na++Ca2+→(R−SO3−​)2​Ca+2Na+

Thus, 2 formula units of resin are required to take up 1 mole of Ca2+Ca^{2+}Ca2+.

  1. Mass of resin required for 1 mole of Ca2+Ca^{2+}Ca2+ uptake

Molar mass of one formula unit of resin = 206206206 g.

So, mass of 2 formula units (in mole terms) = 2×206=412 g2 \times 206 = 412\text{ g}2×206=412 g

Therefore, 412412412 g resin can absorb 111 mole of Ca2+Ca^{2+}Ca2+.

  1. Uptake per gram of resin

Hence, uptake in mole per gram resin is: 1412 mol g−1\frac{1}{412}\text{ mol g}^{-1}4121​ mol g−1

  1. Check options
  • A: 2309\frac{2}{309}3092​ ❌
  • B: 1412\frac{1}{412}4121​ ✅
  • C: 1103\frac{1}{103}1031​ ❌
  • D: 1206\frac{1}{206}2061​ ❌

So the correct option is B.

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