Product at anode of the electrolysis of MgBr2

In summary, oxygen should be formed when oxidation of OH- is attempted, but in practice it is quite slow, so an overpotential is necessary to speed it up. Other than brine and MgBr2, are there any other exceptions to this rule?
  • #1
Janiceleong26
276
4
1. Homework Statement
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Why is the product at anode Br2 for MgBr2? Instead of O2?

Homework Equations

The Attempt at a Solution


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The EΘ value for the oxidation of OH- is -0.40 V,
And that of Br- is -1.07V
And so, shouldn't oxidation of OH- be easier? And hence, O2 is formed at the anode?
 
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  • #2
If memory serves me well, the explanation lies in the kinetics. In general yes, oxygen should be formed. In practice oxygen evolution is quite slow, so you need an overpotential to speed it up, which moves you into the voltages where Br2 is produced. It is the same with brine solutions, where you can easily smell chlorine despite the fact oxygen should evolve first.
 
  • #3
Borek said:
If memory serves me well, the explanation lies in the kinetics. In general yes, oxygen should be formed. In practice oxygen evolution is quite slow, so you need an overpotential to speed it up, which moves you into the voltages where Br2 is produced. It is the same with brine solutions, where you can easily smell chlorine despite the fact oxygen should evolve first.
Woah I see.. How am suppose to know this during the exam ?
Anyways, thanks. Are there any other exceptions other than brine and MgBr2?
 
  • #4
I believe oxygen in general evolves slowly, so whenever it is one of possible products, other things can be produced as well at higher potentials.

Note: I am not entirely sure about this explanation, take it with a grain of salt.
 
  • #5
Borek said:
I believe oxygen in general evolves slowly, so whenever it is one of possible products, other things can be produced as well at higher potentials.

Note: I am not entirely sure about this explanation, take it with a grain of salt.
Alright, thanks!
 
  • #6
Borek said:
If memory serves me well, the explanation lies in the kinetics. In general yes, oxygen should be formed. In practice oxygen evolution is quite slow, so you need an overpotential to speed it up, which moves you into the voltages where Br2 is produced. It is the same with brine solutions, where you can easily smell chlorine despite the fact oxygen should evolve first.

Thank you borek
 
  • #7
Borek said:
If memory serves me well, the explanation lies in the kinetics. In general yes, oxygen should be formed. In practice oxygen evolution is quite slow, so you need an overpotential to speed it up, which moves you into the voltages where Br2 is produced. It is the same with brine solutions, where you can easily smell chlorine despite the fact oxygen should evolve first.
Thank you borek
 

1. What is the product formed at the anode during the electrolysis of MgBr2?

The product formed at the anode during the electrolysis of MgBr2 is magnesium metal.

2. How is the product at the anode determined during the electrolysis of MgBr2?

The product at the anode during the electrolysis of MgBr2 is determined by the reaction at the anode, which involves the oxidation of Br- ions to form Br2 gas.

3. What is the purpose of using MgBr2 in the electrolysis process?

MgBr2 is used in the electrolysis process because it is a source of magnesium ions, which are needed to form the magnesium metal product at the anode.

4. How does the concentration of MgBr2 affect the product at the anode during electrolysis?

The concentration of MgBr2 does not directly affect the product at the anode during electrolysis. However, a higher concentration of MgBr2 will result in a higher concentration of magnesium ions, which can increase the rate of the reaction at the anode.

5. Is the product formed at the anode always the same in the electrolysis of MgBr2?

Yes, the product formed at the anode is always the same in the electrolysis of MgBr2, which is magnesium metal. This is because the reaction at the anode is specific to the oxidation of Br- ions and the reduction of Mg2+ ions, regardless of the concentration of the MgBr2 solution.

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