Pre-Laboratory Questions 1. Complete the table below by calculating the initial

Question

Pre-Laboratory Questions 1. Complete the table below by calculating the initial SCN and equilibrium Fe(SCN)2+ concentrations for each of the five standard solutions. In addition to the volume of KSCN indicated in the table below, each solution contains 5.00 mL of Fe(NO3)3 and sufficient 0.050 M HNOs to produce a total volume of 25.00 mL of solution. Fe3+SCN Fe(SCN)2+ Molarity of KSCN 0.00165 M Molarity of Fe(NO3)3 0.165 M Vol. SCNInitial SCN M Fe(SCN)2+ MAbsorbance 5.00 mL 4.00 mL 3.00 mL 2.00 mL 1.00 mL Solution 1.590 1.320 0.990 0.690 0.335 4

Explanation / Answer

To calculate initial SCN- concentration M2:

Use M1V1 = M2V2 where M1 = 0.00165 M, V2 = 25.00 mL

(1) V1 = 5.00 mL

M2 = M1V1/V2

= 0.00165 x 5.00/25.00

= 3.30 x 10^(-4) M

(2) V1 = 4.00 mL

M2 = M1V1/V2

= 0.00165 x 4.00/25.00

= 2.64 x 10^(-4) M

(3) V1 = 3.00 mL
M2 = M1V1/V2

= 0.00165 x 3.00/25.00

= 1.98 x 10^(-4) M

(4) V1 = 2.00 mL

M2 = M1V1/V2

= 0.00165 x 2.00/25.00

= 1.32 x 10^(-4) M

(5) V1 = 1.00 mL

M2 = M1V1/V2

= 0.00165 x 1.00/25.00

= 6.60 x 10^(-5) M

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