Are these posible experiments possible? Why?

Question

A] When resonably dilute HCl and AgNO3 solutions are mixed , a white AgCl precipitate forms, with some heat involved. When a Na2S2O3 solution is added to this reaction mixture, the white precipitate disappears upon stirring.

Is this possible... would you defend it or Refute it? Why?


B] Some chemist say that the AgCl in (A) dissolves. Others say that AgCl is prevented from precipotating further by the prescence of S2O3 (-2) ion.


Is this possible... would you defend it or Refute it? Why?

Answer 1

You need to understand that the silver ions left in solution (only a few of them, since most of them have precipitated) form a soluble complex with the thiosulphate ions. This upsets the equilibrium between solid silver chloride and aqueous silver chloride to the extent that the solid dissolves to replace the silver ions taken out into the complex. This is a classic example of le Chatelier's Principle.