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Sulfur and Nitric Acid Reaction | S + HNO3

Sulfur and Nitric Acid Reaction | S + HNO3

Nitric acid is an oxidizing acid and it can oxidize sulfur into its higher oxidation states (+4 or +6). According to the temperature of concentrated nitric acid solution, sulfur is oxidized to sulfur dioxide (SO2) or sulfuric acid (H2SO4) acid.



Last update: 2021-04-1


S + HNO3 reaction - sulfur and nitric acid

This is an another example for oxidizing acid behavior of nitric acid. We know, both dilute and concentrated nitric acid can behave as an oxidizing acid.



Sulfur and concentrated nitric acid reaction

Sulfur is oxidized to sulfur dioxide while nitric acid is reduced to nitrogen dioxide.

S + HNO3 → SO2 + NO2 + H2O

Therefore oxidation number of sulfur is changed from 0 to +4. Oxidation number of nitrogen in nitric acid is decreased to from +5 to +4.


Balanced reaction of sulfur and nitric acid reaction

S + 4HNO3 → SO2 + 4NO2 + 2H2O


Sulfur is insoluble in water and exists as a white yellow solid in water. Sulfur dioxide is a colourless gas.




Sulfur and hot concentrated nitric acid reaction

When sulfur reacts with hot concentrated, given products are little bit different from previous reaction.

In this reaction, sulfur is oxidized to sulfuric acid (H2SO4) while nitric acid is reduced to nitrogen dioxide.

S + HNO3 → H2SO4 + NO2 + H2O

Therefore oxidation number of sulfur is changed from 0 to +6. Oxidation number of nitrogen in nitric acid is decreased to from +5 to +4 as previous.


Balanced reaction of sulfur + hot nitric acid reaction

S + 6HNO3 → H2SO4 + 6NO2 + 2H2O

One sulfur mole reacts with six nitric acid moles and produce one sulfuric acid, six nitrogen dioxide and two water molecules.




How to balance reactions?

You saw, in both reactions, oxidation numbers of sulfur is increeased. So these reactions are redox reactions. Now, we are going to learn how to balance these two reactions.


How to balance S + HNO3 → SO2 + NO2 + H2O

First, write oxidation numbers of each element and identify which atoms are oxidized and reduced. Sulfur is oxidized while nitrogen is reduced and oxidation numbers of other elements were not changed during the reaction.

Next, find oxidation number difference of oxidation. For sulfur, this difference is 4. Also determine the oxidation number difference for nitrogen atom. For nitrogen atom, the difference is 1.

Exchange the differences. See the figure. Here, difference of oxidation numbers of oxidation process and difference of oxidation numbers of reduction process are exchanged.

Finally, other atoms (which are not oxidized or reduced) are balanced. There are four hydrogen atoms in the left side. To balance hydrogen atoms, make two water. With that oxygen is also balanced.


how to balance sulfur and nitric acid reaction

In early reactions, you saw, sulfur is oxidized to sulfur dioxide gas by nitric acid. What are the othwr ways of preparing sulfur dioxide gas from sulfur?

Burning sulfur in air will give sulfur dioxide gas. This method is used in sulfuric acid production.




Questions asked by students. Ask your question and find the answer free.


By the reaction of nitric acid and sulfur, will it give a colorful proucts?

Nitrogen dioxide, brown color gas can be given as a colorful product.



In a question, following statement was mentioned. Hydrogen sulfide is oxidized to sulfur by nitric acid. Is this correct?

Yes. This is correct. Hydrogen sulfide is is oxidized to sulfur by nitric acid. Special case is, if more hot nitric acid is available, formed sulfur can be oxidized furthermore to a higher oxidation number.

This is an example to a reaction of an acidic gas and strong acid.



Will sulphur is oxidised by concentrated sulfuric acid like nitric acid

Yes. concentrated sulfuric acid can oxidize sulfur to sulfir dioxide. Also, sulfuric acid is reduce to sufur dioxide gas.


oxidation number of nitrogen in hno3

You can find oxidation number of nitrogen HNO3 by drawing the molecule or using algebra equation.

Using, any of that method, you will find oxidation number of nitrogen is +5.


action of concentrated nitric acid on sulphur equation

Products may vary according to the nitric acid. If, temperature is high, sulfur can be oxidized to sulfuric acid which has its maximum oxidation state, +6. If you use a moderate temperature, sulfur dioxide may be given.


Is it correct to say sulphur reacts with nitric acid?

WE cannot say above statement is not correct 100% because sulphur reacts with concentrated nitric acid. When we say just nitric acid, it may represent dilute or concentrated solutions. So it is good to say sulphur reacts with concentrated nitric acid.


What is the incorrect from following statements about sulphur reacts with nitric acid?

  1. Sulfur is oxidized.
  2. A gaseous compound of sulfur can be given.
  3. Hydrogen is reduced while sulfur is oxidized.
  4. When temperature of nitric acid is increased, sulfur can be oxidized to its +6 oxidation state.



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