3. %u2013 Use the mean value that you determined for Keq to calculate the SCN- c

Question

3. %u2013 Use the mean value that you determined for Keq to calculate the SCN- concentration in a solution Fe3+ concentration was 4.00 X10-2M and initial SCN- concentration was 1.00 X10-3 M. Is all of theSCN- in the form ofFeNCS2+?

Kc=[FeNCS^2+]/[Fe^3+][SCN^-]

AVG Keq= 292

I made the ice chart and determined
Keq=292=(x)/(0.04-x)(0.001-x)

Please show how to solve using algebra.





4. %u2013Does the result of the calculation in question 3 justify our original assumption that all of the SCN- is in the form of FeNCS2+?




5. %u2013 Based upon your answer to question 4 is the measured value of Keq too high or too low?

Explanation / Answer

292=x/(0.04 -x )(0.001-x)

0.01168 - 11.972 x + x^2=x

So x^2 - 12.972x + 0.01168=0

So x=12.971 or 9 x 10^-4

But since 0.001>x

x=0.0009 M

No all the SCN- is not in the form of FeNCS2+

since SCN- left=0.001 - 0.0009=0.0001 M

measured value of Keq is too low

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