For the complete precipitation of of an colloidal sol, exactly of a electrolyte solution is experime — Surface Chemistry Chemistry Question
Question
For the complete precipitation of $200\text{ mL}$ of an $As_2S_3$ colloidal sol, exactly $10\text{ mL}$ of a $1\text{ M } BaCl_2$ electrolyte solution is experimentally required. What is the true flocculation value (in $\text{millimoles L}^{-1}$) of the $BaCl_2$ electrolyte for this specific sol?
Answer: 50
💡 Solution & Explanation
Flocculation (coagulation) value is defined strictly as the minimum millimoles of electrolyte required to coagulate one litre ($1\text{ L}$) of the colloidal sol. Moles of $BaCl_2$ added $= 10\text{ mL} \times 1\text{ M} = 10\text{ millimoles}$. The total volume of the sol coagulated is $200\text{ mL} = 0.2\text{ L}$. Flocculation value $= \frac{10\text{ mmol}}{0.2\text{ L}} = 50\text{ mmol L}^{-1}$.
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