The coagulating power of electrolytes having ions $\mathrm{Na}^{+}, \mathrm{Al}^{3+}$ and $\mathrm{Ba}^{2+}$ for arsenic sulphide sol increases in the order:

(A) $\mathrm{Na}^{+}<\mathrm{Ba}^{2+}<\mathrm{Al}^{3+}$

(B) $\mathrm{Ba}^{2+}<\mathrm{Na}^{+}<\mathrm{Al}^{3+}$

(C) $\mathrm{Al}^{3+}<\mathrm{Na}^{+}<\mathrm{Ba}^{2+}$

(D) $\mathrm{Al}^{3+}<\mathrm{Ba}^{2+}<\mathrm{Na}^{+}$

JEE Main · 2013 · 07 Apr 2013 · Offline · Surface Chemistry

The coagulating power of electrolytes having ions

Na^{+}, Al^{3 +}

and

Ba^{2 +}

for arsenic sulphide sol increases in the order:

(A) $Na^{+} < Ba^{2 +} < Al^{3 +}$ ✓ Correct
(B) $Ba^{2 +} < Na^{+} < Al^{3 +}$
(C) $Al^{3 +} < Na^{+} < Ba^{2 +}$
(D) $Al^{3 +} < Ba^{2 +} < Na^{+}$

Answer: (A)

Solution

Arsenic sulphide sol,

As X_{2} S X_{3}

, is negatively charged, so it is the positive ions of the added electrolyte that bring about coagulation, and by the Hardy-Schulze rule their power climbs steeply with charge. The cations rank

Na X^{+}

(one plus) below

Ba X^{2 +}

(two plus) below

Al X^{3 +}

(three plus), so the coagulating power increases as

Na X^{+} < Ba X^{2 +} < Al X^{3 +}

JEE Main · 2013 · 07 Apr 2013 · Offline · Single correct option

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JEE Main · 2013 · 07 Apr 2013 · Offline · Surface Chemistry

Solution

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