2) You want to determine the concentration of Fe2+ in a solution. You decide to

Question

2) You want to determine the concentration of Fe2+ in a solution. You decide to determine the Fe2+ concentration by means of a redox titration with potassium permanganate. You use 50 mL of the Fe2+ solution and adjust the pH to 1. You need 24.78 mL of a 0.0148 M KMnO4 solution to reach the endpoint. (6 points) a. What is the reaction that takes place? Write the balanced chemical equation. b. What is the concentration of Fe2+ in your original solution? c. What is the balanced chemical equation for the titration of Fe2+ with potassium dichromate? What volume of potassium dichromate (c=0.0148 M) would you have needed for this titration (the pH is acidic)? d. Provide at least two methods to determine the endpoint of the titration with permanganate. Explain exactly how you would determine the endpoint. Do not just state the method.

Explanation / Answer

(a.) MnO4- + 8 H+ + 5 Fe2+ ==> Mn2+ + 5 Fe3+ + 4 H2O

(b) So from reaction , 1 moles of KMNO4 reacts With 5 moles of Fe2+

Now, mole of KMNO4 = .0148 *24.78*10-3 = .36674 *10-3 moles

Let Concentration of Fe2+ = c

Therfore moles of Fe2+ = c*50*10-3 = 50c*10-3 moles

Since, from reaction 1 moles of KMNO4 requires 5 moles of Fe2+

Therfore, .36674 *10-3 *5=50c*10-3

=>c = .036674 M

(c.) 6Fe2+ + Cr2O72

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