38. Solving a chemistry problem

815. Rapid coagulation of 100 ml of arsenic sulfide sol (whose charge is negative) is observed when 13.1 ml of a 0.5 mol/l LiCl solution is added to it. Based on the DLVO theory, estimate what minimum concentration the ZnCl2 solution should have in order for 1 ml of its solution to have a similar effect on the same volume of the As2S3 sol.