The Student Room Group

Unit 2 - Redox question

The question I have is

Solid sodium iodide undergoes a redox reaction with concentrated sulfuric acid.
Give the formula for each of the following in this reaction.

Formula of the solid reduction product -

Formula of the oxidation product -

That is question 3e on http://filestore.aqa.org.uk/subjects/AQA-CHEM2-W-QP-JUN11.PDF

I don't understand how to get the answer :confused:
Sulfuric acid is H2SO4. Sodium Iodide is NaI.
How am I supposed to react these two together? They could make anything?

What i wrote down was HI for the first one
and NaHSO4 for the second :s-smilie:

Any help will be extremely appreciated!
Thank you
Reply 1
Original post by user1-4
The question I have is

Solid sodium iodide undergoes a redox reaction with concentrated sulfuric acid.
Give the formula for each of the following in this reaction.

Formula of the solid reduction product -

Formula of the oxidation product -

That is question 3e on http://filestore.aqa.org.uk/subjects/AQA-CHEM2-W-QP-JUN11.PDF

I don't understand how to get the answer :confused:
Sulfuric acid is H2SO4. Sodium Iodide is NaI.
How am I supposed to react these two together? They could make anything?

What i wrote down was HI for the first one
and NaHSO4 for the second :s-smilie:

Any help will be extremely appreciated!
Thank you


Neither of these are reduced or oxidised.
Reply 2
ok, but i don't understand what it is i am meant to reduce or oxidise?
The soidum or the iodine? The Hydrogen, sulpuhur or Oxygen?
Reply 3
Original post by user1-4
The question I have is

Solid sodium iodide undergoes a redox reaction with concentrated sulfuric acid.
Give the formula for each of the following in this reaction.

Formula of the solid reduction product -

Formula of the oxidation product -

That is question 3e on http://filestore.aqa.org.uk/subjects/AQA-CHEM2-W-QP-JUN11.PDF

I don't understand how to get the answer :confused:
Sulfuric acid is H2SO4. Sodium Iodide is NaI.
How am I supposed to react these two together? They could make anything?

What i wrote down was HI for the first one
and NaHSO4 for the second :s-smilie:

Any help will be extremely appreciated!
Thank you


The reaction is: NaI + H2SO4 ---> I2 + Na2SO4 + H2S + H2O

(it's not balanced)
(edited 11 years ago)
Original post by V95
The reaction is: NaI + H2SO4 ---> I2 + Na2SO4 + H2S + H2O

(it's not balanced)


Solid sulphur is the product in this reaction. H2S is a gas.

As for the oxidation product, think about which species has lost electrons, or which species' oxidation state has gone up

Another way to think about it is that its been oxidised to form the product, therefore its a reducing agent as a reactant. Using your knowledge you should have gained from (big hint here) group 7 metals, and how they react with concentrated sulphurice acid. (Only 2 halide ions are reducing agents in this instant as they reduce H2SO4)
(edited 11 years ago)
Reply 5
I'm sorry, but i still don't understand how you work out the products in the equation

NaI + H2SO4 ---> I2 + Na2SO4 + H2S + H2O

Or if it is meant to be S instead of H2S

Once I have the equation I think I can work out what is the reducing agent and what is the oxidising agent, however I can't get to the equation in the first place.

How would I attain this equation :confused:
Original post by user1-4
I'm sorry, but i still don't understand how you work out the products in the equation

NaI + H2SO4 ---> I2 + Na2SO4 + H2S + H2O

Or if it is meant to be S instead of H2S

Once I have the equation I think I can work out what is the reducing agent and what is the oxidising agent, however I can't get to the equation in the first place.

How would I attain this equation :confused:

In the question they told you a solid was formed. I- ions reduce sulfur(VI) into 3 possible products; SO2, S and H2S. Out of the possible products, which is solid? Therefore that's what the sulfur is reduced to.

2Cl- -> Cl2 + 2e-
H2SO4 + 6H+ + 6e- -> S + 4H2O

6Cl- + H2SO4 + 6H+ -> 3Cl2 + S +4H2O

That's your redox reaction producing solid sulfur
(edited 11 years ago)

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