Question

For the coagulation of $200$ mL of $A{s}_2{S}_3$ solution, $10$ mL of $1M$ $NaCl$ is required. What is the coagulating value of $NaCl$?

• A. $200$
• B. $100$
• C. $50$
• D. $25$

Answer 1

Answer: (C)

$50$

Minimum concentration of an electrolyte in millimole per litre required to cause precipitation of a solution is called coagulation value.
Here, $10$mL of $1M$ $NaCl$ contains $NaCl$ $=10\times 1=10$ mmol.
$200$ mL of $A{s}_2{S}_3$ required $NaCl$ for the coagulation $=10$ mmol.
Therefore, $1000$mL of $A{s}_2{S}_3$ required $NaCl$ for the coagulation $=10\times \frac{1000}{200}=50$ mmol.
So, coagulation value $=50$.