Original post by jezzajoo
Hi was wondering in these diagrams for a level chemistry when the H+ are needed in solution and why.
Not sure what exam board you do, but for AQA H+ is needed in solution when constructing a SHE (Standard Hydrogen Electrode) to measure the electrode potential for a half cell. It must be 1mol.dm^-3 and is generally added via HCl or HNO3. The SHE has an electrode potential of 0.00V and is written on the left by convention. Hydrogen gas is added and a platinum electrode is used as part of the cell. I hope this answers your question
Original post by DanielK1456
Not sure what exam board you do, but for AQA H+ is needed in solution when constructing a SHE (Standard Hydrogen Electrode) to measure the electrode potential for a half cell. It must be 1mol.dm^-3 and is generally added via HCl or HNO3. The SHE has an electrode potential of 0.00V and is written on the left by convention. Hydrogen gas is added and a platinum electrode is used as part of the cell. I hope this answers your question
Thank you very much. That helps with the SHE. However in this question only one side has H+ added and I’m not sure why it s needed.
A student wants to measure the Ecell when ClO- oxidises I- ions.
I2 + 2e- -> 2I- +0.54
ClO + 2H+ 2e- -> Cl- +1.5
the markscheme says you need to add H+ to the solution in the ClO/cl half. I know it’s in the half reaction equation but why is it needed?
Original post by jezzajoo
Thank you very much. That helps with the SHE. However in this question only one side has H+ added and I’m not sure why it s needed.
A student wants to measure the Ecell when ClO- oxidises I- ions.
I2 + 2e- -> 2I- +0.54
ClO + 2H+ 2e- -> Cl- +1.5
the markscheme says you need to add H+ to the solution in the ClO/cl half. I know it’s in the half reaction equation but why is it needed?
A student wants to measure the Ecell when ClO- oxidises I- ions.
I2 + 2e- -> 2I- +0.54
ClO + 2H+ 2e- -> Cl- +1.5
the markscheme says you need to add H+ to the solution in the ClO/cl half. I know it’s in the half reaction equation but why is it needed?
Because there is an oxygen bound to the ClO^- and the only way to get rid of it so it can be reduced to Cl^- is to kick it off as a water molecule. You have the oxygen, the only part missing is the hydrogen.
Original post by jezzajoo
Thank you very much. That helps with the SHE. However in this question only one side has H+ added and I’m not sure why it s needed.
A student wants to measure the Ecell when ClO- oxidises I- ions.
I2 + 2e- -> 2I- +0.54
ClO + 2H+ 2e- -> Cl- +1.5
the markscheme says you need to add H+ to the solution in the ClO/cl half. I know it’s in the half reaction equation but why is it needed?
A student wants to measure the Ecell when ClO- oxidises I- ions.
I2 + 2e- -> 2I- +0.54
ClO + 2H+ 2e- -> Cl- +1.5
the markscheme says you need to add H+ to the solution in the ClO/cl half. I know it’s in the half reaction equation but why is it needed?
It might make sense if you add 1 H2O to the right hand side of the second half equation so everything balances. (ClO- + 2H+ +2e- -> Cl- + H2O) The water is needed on the right to balance out the O in the chlorate ion, and then adding 2H+ balances the hydrogens on the left. e- then balance the charges.
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