Question

If 0.100 mole of AgNO3(s) is added to 300 mL of a 2.00 M NH3(aq) solution, what is [Ag+] in the final solution?

Answer 1

$c=n/V$ , c - solution molarity, n - chemical amount of substance, V - solution volume (L).

The concentration of AgNO₃ is 0,100mol/0,3L=0,333mol/L.The concentration of Ag⁺=0,333mol/L.

Silver forms a complex with ammonia: $Ag^+ +2NH_3 \to [Ag(NH_3)_2 ]^+$

Stability constant of this complex is $K=[Ag(NH_3)_2]^+/[Ag]*[NH_3]^2 =$ 1,075*10⁷

The dissociation of ammonia is neglected. Let the concentration of the complex is x, then the concentration of Ag⁺ is 0,333-x. The concentration of ammonia should be (2,00-x)² but the the resulting equation is difficult, so we can neglect this momemt and resulting equation is

$1,075*10^7 =x/(2,00^2*(0,333-x))$

express x:

$x=1,43*10^7-4,3*10^7x$

$x=0,3326$ mol/L

[Ag⁺]=0,333-0,3326=4*10^-4mol/L

Answer:4*10^-4mol/L