Experiment 3 Data and calculations: Determination of the Equilibrium Constant fo

Question

Experiment 3 Data and calculations: Determination of the Equilibrium Constant for a Chemical Reaction Method II volume in mln volume in mL Depth in mm 2.00 x 10 M Volume in mL Method I 2.00 x 10 M Mixture Fe(NO,, FeSCNP M 104 M 328 10 M 20s x 10 M x 10 M x 104 M: [FeSCN2 in Mixtures to 5 is found by Equation 7. If Method II was used. [FescN? Processing the Data Fe "(aq)+ SCN (aq) A. Calculation of assuming the reaction: 0) This calculation is most easily done by following Steps 1 through 5 in the discussion. Results are to be entered in the table on the following page. If you are using Excel, set up the table as we have, and follow the directions that follow. Stop 1 Find the initial number of moles of Fey and scN- in the mixtures in test tubes 1 through 5. Use Equation 3 and enter the values in the first two columns of the table. step 2 Enter the experimentally determined value of [FescN2 l at equilibrium for each of the mixtures in the next to last column in the table. Use Equation 3 to find the number of moles of FeSCN2 in each of the mixtures, and enter the values in the fifth column of the table. Note that this is also the number of moles of Fey" and SCN- that were used up in the reaction. (continued on following

Explanation / Answer

Find the initial number of moles of Fe3+ and SCN-

For mixture 1 : Initial moles of Fe3+ = 2*10-3 M * 0.005L = 1*10-5 moles

Initial moles of SCN- = 2*10-3M*0.001L = 0.2*10-5 moles

Similarly calculate for remaining mixtures.

Mixture Fe3+ (moles) SCN- (moles)

1. 1*10-5   0.2*10-5

  2. 1*10-5   0.4*10-5

3. 1*10-5   0.6*10-5

4. 1*10-5   0.8*10-5

5. 1*10-5 1*10-5

Now calculate the moles of Fe(SCN)2+ from the experimentally determined concentration of Fe(SCN)2+ for each of the mixture. These are equilibrium moles of Fe(SCN)2+

Experimentally determined concentration(M) Equilibrium moles of Fe(SCN)2+

1. 0.15*10-4   0.15*10-4M*0.010L =0.015*10-5 moles

2. 0.14*10-4 0.014*10-5 moles

3. 0.64*10-4   0.064*10-5 moles

4. 0.85*10-4 0.085*10-5 moles

5. 1.04*10-4   0.104*10-5 moles

This is also the number of moles of Fe3+ and SCN- used up in reaction.

Now calculate the equilibrium moles of Fe3+ and SCN- by subtracting moles of Fe(SCN)2+ from initial moles of Fe3+ and SCN-

Equilibrium moles:

mixture Fe3+ (moles) SCN-(moles)

1. 0.985*10-5   0.185*10-5

2. 0.986*10-5 0.386*10-5

3. 0.936*10-5   0.536*10-5

4. 0.915*10-5   0.715*10-5

5. 0.896*10-5 0.896*10-5

Now calculate the equilibrium concentrations of Fe3+ and SCN- (using total volume = 10mL = 0.010L)

For mixture 1: [Fe3+] = 0.985*10-5moles/0.010L = 0.985*10-3 M

[SCN-] = 0.185*10-5 moles/0.010L = 0.185*10-3 M

Similarly calculate for remaining mixtures. And then calculate the equilibrium constant for each of the mixture as follows:

Ke = [Fe(SCN)2+] / [Fe3+][SCN-] = 0.015*10-3/(0.985*10-3)(0.185*10-3) = 82.3

Similarly calculate for remaining mixtures.

[Fe3+]M*10-3 [SCN-]M*10-3 [Fe(SCN)2+]M*10-3 Ke

1. 0.985 0.185 0.015 82.3

2. 0.986 0.386 0.014 36.8

3. 0.936 0.536 0.064 127.6

4. 0.915 0.715 0.085 129.9

5. 0.896 0.896 0.104 129.5

mean value of Ke = 101.22

Related Questions

Navigate

• Browse (All)
• Browse E
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.