Question

100 ml of 0.2M AlCl₃ is required just to cause coagulation of 700 ml of As₂S₃ sol. what is the flocculation value of AlCl₃?

Answer 1

Coagulation Value: Minimum concentration of an electrolyte in millimole per liter required to cause precipitation of a solution is called the coagulation value.
As per question, 100 ml of 0.2M AlCl₃ contains AlCl₃ =100×0.2=20 millimole.
700 ml of As₂S₃ required AlCl₃ for the coagulation =20 millimole.
Therefore, 1000mL of As₂S₃ required AlCl₃ for the coagulation =$20\times \frac{1000}{700}=28.57$.
So, the coagulation value or flocculation value of AlCl₃=28.57.