Question

Addition of 12 M HCl to saturated NaCl results in precipitation of NaCl. Yet when 1 M HCl is added to the same NaCl solution, no precipitation forms. explain.

Answer 1

When you add concentrated HCl, what you are really adding is H+ + Cl-, and you are pushing the [Cl-] higher. So, to keep Ksp the same, Na+ has to come out of solution in the form of NaCl. If you know the exact volumes involved, you will be able to calculate the amount of NaCl that will come out of solution.

When you add dilute HCl, you are still adding Cl- as well, but you are also adding a lot more water, thus lowering the concentration of all the ions in the solution. So, [Na+][Cl-] will be less than Ksp and nothing will precipitiate.