Chemistry Practice Problems Electrolysis of Water & Mixture of Ions Practice Problems Solution: Write equations for the half-reactions that occur ...

Solution: Write equations for the half-reactions that occur in the electrolysis of a mixture of molten potassium bromide and molten lithium bromide.

Problem

Write equations for the half-reactions that occur in the electrolysis of a mixture of molten potassium bromide and molten lithium bromide.

Solution

We’re being asked to write equations for the half-reactions that occur in the electrolysis of a mixture of molten potassium bromide and molten lithium bromide.


First, we will write the correct formula of the given compounds (refer to periodic Table):


  • potassium bromide = KBr
  • lithium bromide = KBr
    • K = Potassium, Group 1A, charge = +1
    • Li = Lithium, Group 1A, charge = +1
    • Br = Bromine (changed ending to ide in an ionic compound)
      • Group 7A, charge = -1
      • For ionic compounds with the same charges no need to write subscript


Recall that the cathode is where reduction occurs while the anode is where oxidation occurs.


Since both KBr and LiBr are ionic compounds, they form ions (dissociate) in solution: 


  • KBr  K+(aq) + Br(aq)
  • LiBr  Li+(aq) + Br(aq)


During electrolysis, the cation is reduced/gains electrons while the anion is oxidized/loses electrons

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