If I put solid magnesium in a solution of Copper(II) sulfate, what reaction occurs that causes the bubbles? Looking at the Potential tables the only reaction that theoretically occurs is the reduction of copper and oxidation of magnesium...so why there are bubbles? https://www.youtube.com/watch?v=LkUX5vhLjJ0
Answer
Copper (II) sulfate hydrolyzes in water and makes the solution slightly acidic. Then the magnesium is reacting with the weak acid, displacing hydrogen, as well as displacing the copper.
Magnesium displaces hydrogen only slowly with pure water, partly because the magnesium hydroxide product is only sparingly soluble. Just a little acid, even from an ammonium salt or (as here) hydrolysis of a transition metal salt, is enough to dissolve the hydroxide and launch the hydrogen displacement.
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