中三chemistry一問

first of all
the different between brine and sea water is the concentration of sodium chloride
brine is concentrated sodium chloride solution
and sea water is sodium chloride soluton
(i mean mainly, of course they aren't contain sodium chloride only)

when we electrolyze sea water
there are four ions inside
hydrogen ion, sodium ion, hydroxide ion, chloride ion
hydrogen ion and hydroxide ion will discharge first
it's because hydrogen ion is a stronger oxidizing agent than sodium ion
and hydroxide ion is a stronger reducing agent than chloride ion

when we elecrolyze brine
hydrogen ion and chloride ion will discharge first
this is because in brine
the concentration of chloride ion is higher than that in sea water
if the concentration of chloride ion is high enough, it will discharge first

in a chloro-alkali industry
the industry need to get chlorine
so they will choose to electrolyze brine instead of sea water
if they electrolyze sea water, they can't get chlorine gas

when water was electrolysed, its products are oxygen and hydrogen, brine was electrolysed with graphite electrode, its produts are hydrogen and chlorine, if you used mercuy as electrode, sodium will produced, but water will not produce sodium even you use mercury electrode.
Using brine because its salt concentration is much higher than in sea water.

It is because the concentration of the salt in sea water is not saturated.If you electrolyse it, no chlorine will be produced.
Brine means the SATURATED SALT WATER.