Surface Chemistry - Result Question 16
####16. Which of the salt-solution is most effective for coagulation of arsenious sulphide?
(2019 Main, 9 Jan II)
(a) $BaCl _2$
(c) $Na _3 PO _4$
(b) $AlCl _3$
(d) $NaCl$
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Answer:
Correct Answer: 16. $(a, c)$
Solution:
- Arsenious sulphide sol is a negative colloid, $As _2 S _3 .\left(S^{2-}\right)$. So, it will be coagulated by the cation of an electrolyte.
According to the Hardy-Schulze rule, the higher the charge of the ion, the more effective it is in bringing about coagulation. Here, the cations available are $Al^{3+}$ (from $AlCl _3$ ), $Ba^{2+}$ (from $BaCl _2$ ) and $Na^{+}$(from $Na _3 PO _4$ and $NaCl$ ). So, their power to coagulate $As _2 S _3$. $\left(S^{2-}\right)$ will follow the order as
$$ Al^{3+}>Ba^{2+}>Na^{+} $$
