Question

Find the concentration of FeSCN^2+ after 1.0 mL of 0.00020M Fe(NO_3)_3 is combined with 5.0 mL of 1.00M KSCN and 4.0 mL of 0.10M HNO_3.

Answer 1

The general reaction is:

Fe³⁺ + SCN^- ----------> FeSCN²⁺ Kc = [FeSCN²⁺] / [Fe³⁺] [SCN^-]

moles of Fe³⁺ = 1x10^-3 * 0.0002 = 2x10^-7 moles

moles of SCN^- = 5x10^-3 * 1 = 5x10^-3 moles

[Fe³⁺] = 2x10^-7 / 0.010 = 2x10^-5 M

[SCN^-] = 5x10^-3 / 0.010 = 0.5 M

As this is a reaction equilibrium, we need the value of Kc to determine the concentration of this ion so:

[FeSCN²⁺] = Kc [Fe³⁺]eq [SCN^-]eq

The values in equilibrium are:

Fe³⁺ + SCN^- ----------> FeSCN^-

i. 2x10^-5   0.5 0

e. 2x10^-5-x 0.5-x x

x = Kc * (2x10^-5-x)(0.5-x)

Provide this value, or at least the data of absorbance so I can apply the beer law to solve this.

Hope this helps