Question

A common method that is used to organize and calculate the concentrations of the species in an equilibrium system is colloquially known as an I.C.E. chart. “I.C.E” stands for Initial concentration, Change in concentration, and the Equilibrium concentration. Calculate the initial concentrations of the Fe3+ and the SCN– ions in the following reaction recipes. (Show calculation setup for test tube C for full credits)

Test Tube	0.0020 M Fe3+ (mL)	0.0020 M SCN– (mL)	H2O (mL)	[Fe3+] (M)	[SCN-] (M)
A	3.00	3.00	4.00
B	3.00	4.00	3.00
C	3.00	5.00	2.00

Answer 1

The initial concentrations of the reactants can be found from the following relation:

Initial concentration of reactants in mixture

= concentration of stock solution x (Volume of stock solution used/ Total volume of the mixture)

A.

Initial concentration of Fe³⁺ = (2.00 x 10^–3 M) x (0.003 L)/(0.003 L +0.003 L+ 0.004 L) = 6 x 10^–4 M

Initial concentration of SCN^- = (2.00 x 10^–3 M) x (0.003 L)/(0.003 L +0.003 L+ 0.004 L)  = 6 x 10^–4 M

B.

Initial concentration of Fe³⁺ = (2.00 x 10^–3 M) x (0.003 L)/(0.003 L +0.004 L+ 0.003 L)  = 6 x 10^–4 M

Initial concentration of SCN^- = (2.00 x 10^–3 M) x (0.004 L)/(0.003 L +0.004 L+ 0.003 L)  = 8 x 10^–4 M

C.

Initial concentration of Fe³⁺ = (2.00 x 10^–3 M) x (0.003 L)/(0.003 L +0.005 L+ 0.002 L)  = 6 x 10^–4 M

Initial concentration of SCN^- = (2.00 x 10^–3 M) x (0.005 L)/(0.003 L +0.005 L+ 0.002 L)  = 1 x 10^–3 M