Question

2. With the precipitate (AgCl) still present in the test tube, add aqueous ammonia. The precipitate should disappear. This means that silver chloride is soluble in ammonia solution. It is soluble because silver ion and ammonia form a complex called diamminesilver (I) chloride, [Ag(NH3)2]Cl which in solution exists as [Ag(NH)2]* and Cl ions. You could have guessed that this would have happened if you looked over the Table A values of Kr at the end of this lab (and you should also conclude that Pb will probably not forma complex with ammonia!). Use this and the information given in the following box, describe in terms of reactions and calculations why the solubility of silver chloride is increased when aqueous ammonia is added. Hint: think of Le Chatlier's Principle. K sp (AgCI)= 1.8 x 1011 Ki(Ag(NH3)2*)= 1.7 x 10 Qualitative Analysis 129

Answer 1

Agcl dissociates as; Agci - Agt ter iksp 'Nility combine with Agt to form Complex as; Ag+ + 2NH2 ? [Ag (A)2] * ;kf

Adding both ea's Agcl + 2NH2 => ['ng (NH3)2] * ter ik When we add two equations Values of equilibrium constant gets multiplied. → K= ksp Kf =( 108x10"") (1.7 X107) - 3.06 xlo 4 K = 3:06x104 I It is clear from the calculations that on adding NH₃, value of k becomes 3006 to 4 je, higher than ksp and hence equilibrium Shifts forward and more and more Agel gets solubilised to complex lon and cr in.