# Redox titrations

I’m currently stuck on a question on redox titrations and I’m hoping someone can help. Here is the question

This question is about a metal ethanedioate salt, M2C2O4, where M is an unknown metal.
M2C2O4 is analysed by titration with a standard solution of potassium manganate(VII) in acidic conditions. The metal ion does not react with manganate(VII) ions.
2.07 g of M2C2O4 are dissolved in distilled water. The solution is made up to 250 cm3 25.0 cm3 samples of this solution are titrated with acidified potassium manganate(VII)
solution.
26.50 cm3 of 0.0188 mol dm–3 acidified potassium manganate(VII) solution are required for a complete reaction.
5C2O42– + 2MnO4– + 16H+ 10CO2 + 2Mn2+ + 8H2O Calculate the relative atomic mass of the unknown metal, M.
Identify M.
Original post by M654321
I’m currently stuck on a question on redox titrations and I’m hoping someone can help. Here is the question

This question is about a metal ethanedioate salt, M2C2O4, where M is an unknown metal.
M2C2O4 is analysed by titration with a standard solution of potassium manganate(VII) in acidic conditions. The metal ion does not react with manganate(VII) ions.
2.07 g of M2C2O4 are dissolved in distilled water. The solution is made up to 250 cm3 25.0 cm3 samples of this solution are titrated with acidified potassium manganate(VII)
solution.
26.50 cm3 of 0.0188 mol dm–3 acidified potassium manganate(VII) solution are required for a complete reaction.
5C2O42– + 2MnO4– + 16H+ 10CO2 + 2Mn2+ + 8H2O Calculate the relative atomic mass of the unknown metal, M.
Identify M.

What have you tried, so far?
Original post by Pigster
What have you tried, so far?

So far I calculated the moles of potassium manganite (V11) and then used the mole ratio of 5:2 to calculate the moles of oxylate ions which come from the metal ethandioate. I then used Mr=mass/moles to calculate the Mr of the entire metal ethandioate. I then subtracted the Mr of the remaining part of the molecule (C2O4) from the total Mr of the molecule and got 78.2 which is the Mr of M2 the Mr of 1 mole of the metal (M) is therefore 78.2/2=39.1 and the answer I got was potassium. However I don’t think this is correct because the question says the metal ion does NOT react with manganite ions which I’m sure a potassium ion in this case will react with manganate ions. Can you please confirm if this is correct?
Original post by M654321
So far I calculated the moles of potassium manganite (V11) and then used the mole ratio of 5:2 to calculate the moles of oxylate ions which come from the metal ethandioate. I then used Mr=mass/moles to calculate the Mr of the entire metal ethandioate. I then subtracted the Mr of the remaining part of the molecule (C2O4) from the total Mr of the molecule and got 78.2 which is the Mr of M2 the Mr of 1 mole of the metal (M) is therefore 78.2/2=39.1 and the answer I got was potassium. However I don’t think this is correct because the question says the metal ion does NOT react with manganite ions which I’m sure a potassium ion in this case will react with manganate ions. Can you please confirm if this is correct?

K+ wouldn't react with manganate(VII). You are even told that you are using potassium manganate(VII).
Ok so is this correct?
(edited 2 years ago)
Original post by M654321
Ok so is this correct?

TBH, I haven't got my calculator out, but your method reads correct and since you've got an Ar of 39.1 which exactly fits K and since K fits the formula of the unknown, then I have fantastic confidence in you.