Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
Excess zinc dust is stirred into copper(II) sulphate until the reaction is at equilibrium. The standard emf is and . Find at . Then find the concentration of left, and give it as , in the way that pH is given. Take to be , since almost all the copper ion has reacted.
, with , and at . A reaction with has and . When half-reactions with different numbers of electrons are added, add the Gibbs energies, not the potentials.
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. log K. , so .
Step 2. The quotient at equilibrium. , because the solids are left out.
Step 3. The copper ion. .
Step 4. As a power of ten. .
Answer: , and , so .
Check. That is about one ion in litres. For every practical purpose, the reaction has gone to completion.
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