MnO4¯ + 8H^+ +5Fe^2+ → Mn^2+ + 4H2O + 5Fe^3+
Which ones underwent oxidisation and reduction.
My answer is Mn and O went oxidisation and Fe and H went reduction but it's wrong and I don't understand why. Any help is very much appreciated. Thanks
iron goes from Fe^2+ to Fe^3+ ... the oxidation number increases
... iron is oxidized
Mn goes from +7 in MnO4¯ to Mn^2+ ... the oxidation number decreases
... manganese is reduced
5 irons lose an electron , one manganese gains 5 electrons ... balanced
H and O don't change oxidation states
In the given chemical equation:
MnO4¯ + 8H^+ + 5Fe^2+ → Mn^2+ + 4H2O + 5Fe^3+
Oxidation involves an increase in oxidation number, while reduction involves a decrease in oxidation number.
Looking at the reaction, we can determine the oxidation numbers of each element:
In MnO4¯, the oxidation number of Mn is +7 and the oxidation number of O is -2. In Mn^2+, the oxidation number of Mn is +2.
In Fe^2+, the oxidation number of Fe is +2. In Fe^3+, the oxidation number of Fe is +3.
In H^+, the oxidation number of H is +1. In H2O, the oxidation number of H is +1 and the oxidation number of O is -2.
Now, let's analyze the changes in oxidation numbers for each element:
- Mn changes from +7 to +2, so it undergoes reduction (decrease in oxidation number).
- O changes from -2 in MnO4¯ to -2 in H2O, so there is no change in oxidation number for O.
- Fe changes from +2 to +3, so it undergoes oxidation (increase in oxidation number).
- H changes from +1 in H^+ to +1 in H2O, so there is no change in oxidation number for H.
Based on this analysis, the correct answer is: Mn underwent reduction and Fe underwent oxidation. O and H were not involved in either oxidation or reduction in this reaction.
To determine which species underwent oxidation (loss of electrons) and which underwent reduction (gain of electrons) in a reaction, you can assign oxidation states to each element within the compounds involved.
In the given equation:
MnO4¯ + 8H^+ + 5Fe^2+ → Mn^2+ + 4H2O + 5Fe^3+
First, let's assign oxidation numbers to the elements based on some rules:
- Oxygen (O) usually has an oxidation state of -2, except in peroxides (-1) or when it combines with highly electronegative elements like fluorine (+2).
- Hydrogen (H) typically has an oxidation state of +1, except when it is bonded with metals, then it has a -1 oxidation state.
- The sum of the oxidation states in a neutral compound is zero, and it is equal to the charge of the ion in an ionic compound.
Based on these rules, we can assign the oxidation states as follows:
MnO4¯: Mn has a +7 oxidation state, and O has a -2 oxidation state.
H^+: H has a +1 oxidation state.
Fe^2+: Fe has a +2 oxidation state.
Mn^2+: Mn has a +2 oxidation state.
H2O: H has a +1 oxidation state, and O has a -2 oxidation state.
Fe^3+: Fe has a +3 oxidation state.
Now let's analyze the changes in oxidation states:
- Mn went from oxidation state +7 in MnO4¯ to +2 in Mn^2+. It gained 5 electrons, so it underwent reduction.
- O went from -2 in MnO4¯ to -2 in H2O. It did not change its oxidation state.
- H went from +1 in H^+ to +1 in H2O. It did not change its oxidation state.
- Fe went from +2 in Fe^2+ to +3 in Fe^3+. It lost 1 electron, so it underwent oxidation.
Therefore, the correct answer is:
Mn underwent reduction, and Fe underwent oxidation.
I hope this explanation helps you understand how to determine oxidation and reduction in a reaction.