Coagulating value of the electrolytes AlCl₃ and NaCl for As₂ S₃ are 0.09 and 50.04 respectively. The coagulating power of AlCl₃ is x times the coagulating power of NaCl. The value of x is ___________.

Solution

Chemistry ma’am · 4 steps

A smaller coagulating value means a stronger coagulant, so divide NaCl's value by AlCl3's.

1. What the value means. The coagulating value is the minimum concentration of electrolyte (in millimoles per litre) needed to coagulate the sol. An electrolyte that works at a lower concentration is a more powerful coagulant.
2. Inverse relation. So coagulating power is inversely proportional to coagulating value. The ratio of the two powers is the inverse ratio of the two values.

   x = power(AlCl₃)/power(NaCl) = value(NaCl)/value(AlCl₃) = 50.04/0.09

3. Why so large. As₂S₃ is a negative sol, so the cations do the coagulating. By the Hardy–Schulze rule, Al³⁺ is far more effective than Na⁺, and a ratio in the hundreds fits that.
4. So. x = 50.04/0.09 = 556, so AlCl₃ is 556 times as powerful a coagulant as NaCl.

The common slip: 0.0018. Dividing the other way round, 0.09 by 50.04, gives about 0.0018, not 556. That compares the values, not the powers.

The idea to keep. Coagulating power is 1 divided by coagulating value. To compare two electrolytes, put the weaker one's value on top, and expect a higher-charged counter-ion to win by a wide margin.

Answer from the NTA final answer key. Solution by PrepWiser.