H₂S Oxidation Number | Oxidation State of Sulfur in H₂S

Sulfur forms different oxidation numbers from -2 to +6. Also hydrogen has different oxidation numbers, -1, 0, +1 . We can find oxidation numbers of sulfur and hydrogen in H₂S by several methods.

In H₂S molecule, oxidation numbers of sulfur and hydrogen are -2 and +1 respectively. Now in this tutorial, we are going to learn how those oxidation numbers are found in different ways.

Determining oxidation numbers of H₂S

1. From drawing the structure of molecule
2. From algebra equation

First, we should have an idea about electronegativities of sulfur and hydrogen atoms.

electronegativities of sulfur and hydrogen

According to the Pauling 's scale, electronegativity of sulfur (2.5) is higher than hydrogen (2.1) . So hydrogen atom is oxidized while sulfur atom is reduced in S-H bond.

From drawing structure of molecule

There are two S-H bonds in H₂S molecule. Due to higher electronegativity of sulfur, electrons of bond are attracted towards sulfur atom. So hydrogen looses its electrons and gets +1 oxidation state. So sulfur takes two electrons from two hydrogen atoms in two S-H bonds, therefore oxidation number of sulfur is -2.

Calculate Oxidation state from algebraic equation

We know in H₂S, hydrogen atom is oxidized and it's oxidation number is +1 and there are two hydrogen atoms. Oxidation number of sulfur is unknown and take it as x. Then substitute those values to the algebraic equation.

• Summation of oxidation numbers of all elements = charge of H₂S
• Summation of oxidation numbers of hydrogen + Summation of oxidation numbers of sulfur = 0
• [ (+1) * 2 ] + [x] = 0
• x = -2

Importance of oxidation states of sulfur and hydrogen

According to the oxidation number, we can say, whether that atom can be oxidized or reduced or both occurred. Now, we are going to study that.

• Oxidation number of sulfur in H₂ is -2. So that sulfur atom can be oxidized to sulfur's other higher oxidation states such as 0, +2 and +6. But, sulfur atom cannot be reduced furthermore because -2 is the lowest oxidation state of sulfur.
• Oxidation number of hydrogen in H₂ is +1. So that hydrogen atom can be reduced to hydrogen's other lower oxidation states such as 0 and -1. But, hydrogen atom cannot be reduced furthermore because +1 is the highest oxidation state of hydrogen.

Why hydrogen has positive oxidation number while sulfur has a negative oxidation number in H₂S?

Take electronegativity values of sulfur and hydrogen. Sulfur's electronegativity value is 2.5 and hydrogen's it is 2.1 . When electronegativity is higher of an atom, that atom can attract the electrons of the bond and gets more electrons than the protons of the its nucleus. So sulfur has a negative oxidation number in H₂S.

If oxidation number of sulfur in H₂S is -2, are there any sulfur compounds which have sulfur is at -2 oxidation state? Give examples

We know, sulfur can show different oxidation numbers. When sulfur is combined with metals, oxidation number of sulfur become -2 because sulfur takes two electrons from two sodium atoms. As an example, oxidation number of sulfur in sodium sulfide is -2.

How would you say H₂S can be oxidized from its -2 oxidation state?

When H₂S reacts with oxygen (combustion), S in H₂S is oxidized to +4 oxidation state, sulfur dioxide.

How do you prove H₂S can be behaved as an oxidizing agent, from oxidation of H₂S ?

H₂S reacts with sodium and produce sodium sulfide and hydrogen gas. Hydrogen at +1 oxidation state in the H₂S is reduced to 0 oxidation state while sodium is oxidized from 0 to +1. So H₂S is behaved as an oxidizing agent.

Is there a similarity in oxidation numbers of H₂S and H₂O

Both sulfur and oxygen has higher electronegativity values than hydrogen. Therefore, hydrogen is oxidized with both sulfur and oxygen. So hydrogen oxidation number is +1. Sulfur and oxygen have -2 oxidation number in H₂S and H₂O respectively.

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