Chemistry question reduction

Compare the oxidation states of each element in the compounds:
KNO3: KNO2:
K = 1+ K = 1+
N = 5+ N = 3+
O = 2- O = 2-

The oxidation state of N decreases from 5+ to 3+ therefore N has gained 2 electrons. Reduction is gain of electrons therefore N has been reduced.

Ahhh that makes sense, so none of the elements are being oxidised? Does oxidation always take place when reduction takes place?

Yes (in the context of electrons) because when electrons are lost by a substance in oxidation, they must be gained by another substance/ reduce another substance as they are both reactants. You can't have free electrons not associated with any element for a normal reaction like this.

So what will be oxidised since the oxidation states for all the other elements remain the same?

Sorry for the late response.

In the reactant, KNO3 has the following oxidation states:

K=+1 (always true for group 1 metals)
O= -2 (always true for oxygen except for in hydrogen peroxide) but it's O3 so -2 x 3= -6
This means that N is equal to +5 to balance out the earlier charges

For the products, K= +1, O= -2x2= -4 so N is =3+

However, O2 has no charge (0) because it exists in its elemental form, oxygen is naturally found as O2. This means that Nitrogen has been reduced and oxygen has been oxidised.

Compare the oxidation states of each element in the compounds:
KNO3: KNO2:
K = 1+ K = 1+
N = 5+ N = 3+
O = 2- O = 2-

The oxidation state of N decreases from 5+ to 3+ therefore N has gained 2 electrons. Reduction is gain of electrons therefore N has been reduced.

Please could someone explain how nitrogen is being reduced in this equation? Thanks!

2KNO3 —> 2KNO2 + O2

Good explanation, could not do it better. But if two electrons are gained, the question is, which element gives them? oxidation means a change of oxidation number too, but the only number that is changed in your comparison is Nitrogen, the other elements have not been changed.

Good explanation, could not do it better. But if two electrons are gained, the question is, which element gives them? oxidation means a change of oxidation number too, but the only number that is changed in your comparison is Nitrogen, the other elements have not been changed.

I thought two electrons from the six oxygen in KNO3 would reduce the nitrogen to 3+ but I am confused as to where the other 4 electrons would go from that because I thought since oxygen is in its elemental form it would remain 0

Ahh well the question was specifically asking about the N in the equation so I ignored the O2 but if we are to compare the oxidation states for the entire equation then:

KNO3: KNO2: O2:

K = 1+ K = 1+
N = 5+ N = 3+
O = 2- O = 2- O = 0

As you can see, the oxidation state of O increases from 2- to 0 therefore O has lost 2 electrons (these are the ones that N gains).