Homework Help: Chemistry

Posted by Bob on Sunday, April 3, 2011 at 4:51pm.

This is for a lab about determining the equilibrium constant.
Given: 5.00mL of .203M Fe(NO3)3 mixed with 100mL of .00205M KSCN in a .5M HNO3 solvent for both solutions. Resulting absorbance for solution is .315.

How can i find the total Fe, [Fe*] and SCN, [SCN*] in the system without determining equilibrium values of [FeSCN+2], [Fe+3], and [SCN-].

What i know so far is that:
Fe+3 + SCN- makes FeSCN+2
[Fe*] = [Fe+3] + [FeSCN+2]
[SCN*] = [SCN-] + [FeSCN+2]

Chemistry - DrBob222, Sunday, April 3, 2011 at 5:10pm
Make an ICE chart.
Total Fe = moles Fe(NO3) = 5.00 mL x 0.203 M = ??millimoles Fe.
Total SCN = mL x M = 100 x 0.00205 = ??millimoles SCN
...............Fe^+3 + SCN^- ==> FeSCN^+2
initial......
change.......
equil........

One caution here. The ICE chart prepared as above is done with millimoles. Before you can use this to determine a Keq value, millimoles must be changed to M which = millimoles/TOTAL mL.
Total mL in this case is 105 mL.

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