Simple cell question

Question

i have a simple cell. cooper and magnesium electrode.

the electrolyte is dilute sulphuric acid,

what is the gas evoked at the copper electrode?

my teacher said that it is oxgen gas, but i don't understand why.

Answer 1

Sorry, but I don't agree with your teacher.  Oxidation of magnesium occurs at the magnesium electrode (anode).  Reduction of H+ to hydrogen occurs at the copper electrode (cathode) by the following reaction:

2H+ (aq) + 2e- --> H2 (g)

Once the acid is exhausted, water will begin to be reduced instead according to the reaction:

2H2O (l) + 2e- --> H2 (g) + 2OH- (aq)

The gas bubbles given off at the copper electrode in both reduction reactions are  hydrogen, not oxygen.

With a metal as easy to oxidize as magnesium in the cell, there is no way water will oxidize instead to produce oxygen gas.