Iron(II) can be oxidized to iron(III) by permanganate ion in acidic solution. The permanganate ion is reduced to manganese(II) ion.
(a) Write the oxidation half-reaction, the reduction half-reaction, and the overall redox equation.
(b) Calculate E° for the reaction.
(c) Calculate the percentage of Fe in an ore if a 0.3500-g sample is dissolved and the Fe2+ formed requires for titration 55.63 mL of a 0.0200 M solution of KMnO4.
(a)
Interpretation:
The oxidation half, reduction half and overall redox reaction should be written for the given reaction.
Concept introduction:
The redox equation can be balanced by following a few steps:
Step 1: Split the reaction into two halves; oxidation and reduction half.
Step 2: The half reaction should be balanced.
Step 3: Number of electrons should be made equal in both the reaction halves by multiplying with suitable coefficients.
Step 4: The half reactions should be added and electrons should be cancelled to get final reaction.
Step 5: General reactions can be balanced by balancing the number of atoms of each element in the molecules of both the LHS and RHS sides.
Answer to Problem 39QAP
The oxidation half is:
The reduction half is:
The redox reaction is:
Explanation of Solution
Given:
Iron (II) can be oxidized to iron (III) by permanganate ion in acidic medium. The permanganate ion is reduced to manganese (II) ion.
From the given reaction details first of all, the oxidation half is written as where the iron (II) is oxidized to iron (III):
Step1: Oxidation half-reaction:
Step 2: In reduction half-reaction the permanganate ion is reduced to manganese (II) ion as:
Step4: Both the halves are added to get redox reaction as:
Hence, the balanced redox equation is
(b)
Interpretation:
The E0 of the reaction should be calculated.
Concept introduction:
For any redox reaction, the
Since, for the same reaction the oxidation process will be reverse of reduction, so to obtain the oxidation potential, check for the reduction potential of the reverse reaction.
Answer to Problem 39QAP
Explanation of Solution
The reduction potential for oxidation ands reduction half reactions are:
The oxidation half-reaction is:
The reduction half-reaction is:
Hence the E° value is obtained as:
(c)
Interpretation:
The percentage of Fe in an ore should be calculated.
Concept introduction:
The moles of any compound or element can be calculated by given formula:
Where n is the number of moles, m is the given mass and M is the molar mass of the element/compound.
From the given formula, the mass is also calculated as:
For the calculation of mass %, the basic formula is used as:
Answer to Problem 39QAP
The percentage of iron in the ore by mass is 87.7 %.
Explanation of Solution
Given:
The amount of ore dissolved is 0.3500 g and the Fe+2 formed require 55.63 mL of a 0.0200 M solution of KMnO4 for titration.
The balanced equation of redox titration of Fe+2 is:
Here, 5 moles of
Here, for the KMnO4 solution, the molarity is 0.0200 M and volume taken is 55.63 mL.
The volume in L will be:
Now, as one mole of KMnO4 gives one mole of
Since, the Fe+2 reacts with
Thus, the mass of Fe used is:
The mass % of Fe in ore is:
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Chapter 20 Solutions
OWLV2 FOR MASTERTON/HURLEY'S CHEMISTRY:
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