:Determination of the Equilibrium Constant for a Chemical Reaction Data and Calc

Question

:Determination of the Equilibrium Constant for a Chemical Reaction Data and Calculations: Determination in ml.. Volume in ml. 2.00 × 10-3M Fe(NO) Volume in ml. 2.00 × 10-3M KSCN Volume in mL Water Method I Absorbance Method II Depth in mm Mixture Standard Unknown 0.037 13-0.143 -2-0.249 - L 0.371 FeSCNI* 2.00x 10M 4.00× 10-w 6.00x 10 8.00 × 10 LO 10 5.00 1.00 5.00 5.00 3.00 4 5.00 5.00 If Method 11 was used. [FeSCN2+1 10-4 M: [FeSCN2+] in Mixtures 1 to 5 is found by Equation 7. = andard Fe(SCN (ag)

Explanation / Answer

Ok to understand this better, I will do calculations for the first to measures, the other three try to do it yourself following the same procedure.

First the overall reaction along with a ICE chart (This for the first values)

r: Fe3+ + SCN- = FeSCN2+

i: 1x10-6  2x10-6   0

e: 1x10-6-x 2x10-6-x x

Kc = (x2/10) / (1x10-6-x) (2x10-6)/10

This is the general expression to calculate Kc. Now according to the first sheet you already calculated the concentration of the complex FeSCN, so, with that and the total volume (which is 10) you can calculate the equilibrium moles of the complex. The concentration of the complex in the equilibrium is also the value of "x" in the expression of Kc, so for this first calculations:

moles FeSCN = 2x10-4 * 0.010 = 2x10-6 moles

Now in here, we have the following problem and is the fact that if you substract this moles to the moles of Fe and SCN, you will get 0 for one and -1x10-6 moles. And this would be wrong. I think that you got wrong in the values of FeSCN, you need to check that. How did you obtain those values?.

However, once you correct that value the moles in equilibrium for both reactants would be the innitial moles - equilibrium moles of complex. and the concentration would be the dividing the moles by the total volume which is 01 mL (0.010 L).

Now, how can we obtain the value of the complex in equilibirum? we have the absorbance for the complex. Do you have the value of E (molar absorptivity of the complex)? if you have that value, just apply beer law:

A = EbC assume b = 1 cm

then solve for C:

C = A/Eb

With that you can calculate the value of C, that it would be the complex concentration in equilibrium, and then, you can calculate the moles and concentration in equilibrium. Check your results and previous calculations, so I can help you better. Then, once you have the corrected values, post them again in a different post if you still need help.

Hope this information and guidance, helps you.

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