The moles of electrons used per mole of manganese is therefore
Since it requires 7 electrons to bring a manganese ion to an oxidation state of 0, the ion must have had an original charge of +7. The original ion was therefore . The rounding in equation (4) is not only justified by the approximations of the earlier calculations, it is actually necessary. Manganese cannot have an oxidation state of 6.984; oxidation states must be integers. Therefore, it is reasonable to assume that a difference between the calculated answer and an integer value is caused by rounding errors and that the integral value is in fact a better answer.
