We have 0.05M Pb (SO4) 2
0.03M Cr (NO3) 2
To begin with, we exclude all non-electrolytes, since they do not have a coagulating ability, - Pb (SO4) 2 Li3PO4 Ba2XeO4 AsCl5 PbCl2. The following solutions remain 0.003M SnCl2 0.07M CrCl3 0.03M Cr (NO3) 2 0.0006M NaCl 0.02M MgCl2 0.07M AlCl3 0.11M BaCl2 0.04M SnCl4 0.005M BeBr2 0.006M CaBr2. The coagulating ability is possessed by an electrolyte ion, which is opposite to the charge of the granule, that is, it coincides with the sign of the PI charge. Of all the electrolytes, there are Cl- Br- and NO3- anions, according to the Schulze-Hardy rule, the coagulating ability of the coagulant ion is the greater, the greater the charge of the ion, but since we all have the same charge, all the anions have the same coagulating ability. it follows that the coagulation threshold is the same for all solutions.
Then from the formula Cpc = Cel * Vel / Vsol + Vel, for the proposed solutions, whose coagulation thresholds are the same, it follows that the higher the concentration of the electrolyte, the less V of this solution is required. (proof - let the coagulation threshold for the 1st and 2nd electrolyte be the same and equal to 0.5 mmol / L, and Vsol 5 L. The concentration of the 1st solution is 0.6M, and the 2nd solution is 0.8M, and Vel is taken as X.
for the first solution 0.5 = 0.6 * x / 5 + x, hence x = 25l, that is, at a concentration of -0.6M, you need to take 25 liters of electrolyte
for the second solution 0.5 = 0.8 * x / 5 + x, hence x = 8.3 l, therefore, at a concentration of 0.8M, you need to take 8.3 l
CONCLUSION - the volume and concentration of the values are inversely proportional, with an increase in concentration, less electrolyte volume is required for coagulation)
Therefore, it is necessary to choose a solution with a higher concentration - this is BaCl2 0.11M. Consequently, a particle can be coagulated with a smaller volume of BaCl2 with a concentration of 0.11M.