In: Chemistry
The initial concentrations of Na+ and Cl− in the reaction below are each 0.0843 M. If the initial concentration of NaCl is 0 M and the equilibrium constant is Kc=8.21 under certain conditions, what is the equilibrium concentration of Na+?
NaCl(aq)⇌Na+(aq)+Cl−(aq)
NaCl(aq) Na+(aq) + Cl-(aq)
Equilibrium constant Kc = = 8.21
The solution technique involves ICE box, where 'I' represents Initial, 'C' represents Change, 'E' represents Equilibrium. An empty ICE box looks like:
The complete table is
Here 'x' is unknown. For [Na+] and [Cl-] we represent - x because the amount is going down as reaction proceeds. Thus the amount of [NaCl] goes up till equilibrium reaches. At equilibrium the concentration is shown in the box.
Kc =
By solving this quadratic equation,
x= (8.3786+8.3769)/2 and (8.3786-8.3769)/2
= 8.3778M and 0.00085M
The x = 0.00085M ( 0.0843-x is - ve, so neglected)
The equilibrium concentration of Na+ = 0.0834 - 0.00085
= 0.08255M