Balance the equation for the reduction of MnO4- to Mn2+

Balancing equations is usually fairly simple. However some of them involve several steps.

You may have come across balanced equations in data booklets that look intimidating. The balanced equation for reduction of Mn7+ to Mn2+ is one such equation.

Initially one might write:

Mn7+ + 5e- --> Mn2+

Although technically balanced (since the ox state of Mn in MnO4- is +7), this equation does not represent the full reaction that takes place which involves H2O molecules and H+ ions.

The fully balanced equation is:

MnO4- + 8H+ + 5e- --> Mn2+ + 4H2O

To balance this, the following steps must be followed:

Step 1: Write only what's given. 

MnO4- --> Mn2+

Step 2: Balance all atoms except for H and O.

MnO4- --> Mn2+ (Mn atoms are already balanced; one on each side).

Step 3: Balance Oxygen atome by adding H2O to the side where more oxygen atoms are needed. At this stage, we have 4 O atoms on the left hand side and need 4 on the RHS. One water molecule contains one O atom, so we need 4 water molecules.

Therefore, MnO4- --> Mn2+ + 4H2O

Notice that now we have 4 O atoms on each side but 8 H atoms on the RHS.

Step 4: Balance H atoms by adding the required number of H+ ions to the side that is short of H atoms. At this stage we have (4 x 2) 8 H atoms on the RHS and none on the LHS.

Therefore, MnO4- + 8H+ --> Mn2+ + 4H2O

Step 5: Balance the charges by adding an electron, e-. At this stage, the LHS has a  (-1 +8)  +7 charge. The RHS has a +2 charge. If we add 5e- to the LHS, the charge becomes 7 - 5 = +2

Therefore, MnO4- + 8H+ + 5e- --> Mn2+ + 4H2O

By the end of step 5, we have obtained the fully balanced equation.

You can balance any equation using these steps, however, there is a slight adjustment that has to be made to step 4 sometimes.

In acidic solutions, to balance H atoms you just add H+ to the side lacking H atoms but in a basic solution, there is a negligible amount of H+ present. Instead, OH- is abundant. In this case, you add H2O to the side lacking H atom(s) and a OH- to the opposite side. The net effect is that you end up adding 1 H atom to the side that lacks a H atom. If a side lacks 'n' number of H atoms, add 'n' number of H2O molecules to that side and 'n' number of OHions to  the opposite side.

Haroon A. GCSE Maths tutor, GCSE Chemistry tutor, GCSE Physics tutor,...

8 months ago

Answered by Haroon, a GCSE Chemistry tutor with MyTutor

Still stuck? Get one-to-one help from a personally interviewed subject specialist


Luke C. A Level Biology tutor, GCSE Biology tutor, A Level Chemistry ...
View profile
£18 /hr

Luke C.

Degree: Biological Sciences with a year in professional placement (Bachelors) - Exeter University

Subjects offered: Chemistry, Maths+ 1 more


“My greatest passion is for biology, but I have always enjoyed studying chemistry and mathematics too. Studying these subjects has supported me during my time so far at Exeter University, even though I am still in my first year of stud...”

MyTutor guarantee

PremiumHannah S. GCSE Biology tutor, GCSE Chemistry tutor, A Level Chemistry...
View profile
£22 /hr

Hannah S.

Degree: Medicinal Chemistry and Pharmacology (Masters) - Liverpool University

Subjects offered: Chemistry, English Language+ 2 more

English Language

“I'm currently studying medicinal chemistry and pharmacology at the University of Liverpool as part of an 'integrated masters' course designed to fast track students interested in a chemistry as a profession or continuing study to a PhD...”

Shannon W. 13 plus  Maths tutor, 11 Plus Maths tutor, A Level Maths t...
View profile
£18 /hr

Shannon W.

Degree: Chemistry with Medicinal Chemistry (Masters) - Newcastle University

Subjects offered: Chemistry, Science+ 3 more

-Personal Statements-

“About me: I am a chemistry student at Newcastle University. I have always been interested in science and mathematics, and can sit for hours watching documentaries on the subjects. I really enjoy getting stuck into exam questions and ...”

About the author

Haroon A. GCSE Maths tutor, GCSE Chemistry tutor, GCSE Physics tutor,...
View profile

Haroon A.

Currently unavailable: until 01/06/2016

Degree: Chemical Engineering with Industrial experience (Other) - Manchester University

Subjects offered: Chemistry, Physics


“I am currently studying Chemical Engineering at the University of Manchester. The reason I have chosen to adopt engineering as my profession is because engineers make a difference. Engineers are able to take the knowledge derived from...”

MyTutor guarantee

You may also like...

Posts by Haroon

Balance the equation for the reduction of MnO4- to Mn2+

The polynomial x^3 - 2*x + a, where x is a constant is denoted by p(x). It is given that x+2 is a factor of p(x). Find a

Other GCSE Chemistry questions

Explain why fluorine and chlorine are in the same group of the periodic table.

Why can graphite conduct electricity?

Basic Reactions of Acids.

What does the periodic table show you?

View GCSE Chemistry tutors


We use cookies to improve our service. By continuing to use this website, we'll assume that you're OK with this. Dismiss