A sample was made by mixing 5.00 mL of 0.00200 M Fe^3+ with 3.00 mL of 0.0020 M

Question

A sample was made by mixing 5.00 mL of 0.00200 M Fe^3+ with 3.00 mL of 0.0020 M SCN^-and 2.00 mL of 1.0 M HNO_3. The resulting solution had a transmission of 15.8% (T = 0.158). Calculate the initial concentrations of Fe^3+ and SCN^- and enter them in the ICE chart below. (Show your work. These are just dilution calculations.) Calculate the absorbance from the percent transmission. Then use the graph from problem 1 (or its best-fit equation) and the absorbance to find the equilibrium concentration of FeSCN^2+ in this sample. Enter this concentration in the ICE chart. Continued on next page.

Explanation / Answer

Initially:

Total V = V1+V2+ = 5 mL + 3 mL = +2mL = 10 mL

Fe3+ = M1V1/VT = 5*0.002/10 = 0.0010 M

SCN- = M2V2/VT = 3*0.002/10 = 0.0006 M

Fe(SCN)2+ = 0

the change:

Fe3+ = -x

SCN- = -x

Fe(SCN)2+ = +x

in equilibrium:

Fe3+ = 0.0010 -x

SCN- = 0.0006 -x

Fe(SCN)2+ = 0 + x

b)

Calculate A:

A = -log(T%/100) = - log(0.158) = 0.8013

0.001 - x +0.0006 -x + x = C

NOTE, frm your "problem 1 best fit equation" get Concentration from Absorbance, then substute to get "X"

afterwards, get all concentration values substituting "X"

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