CHEMISTRY: single replacement net and total ionic equations!?

[Boston]

I guess everyone beat me to it. Anyway, here's my two cents: Here the reaction deals with redox chemistry. You mention Mg has no charge on the left, but it does have a charge on the right. Think of it as which metal (Mg or Cu) want's to have a charge more. In this case, it is Mg. Check out the picture and movie of what magnesium does in a similar reaction (this case with Ag instead of Cu and nitrate instead of sulfate)

http://www.webelements.com/webelements/elements/text/Mg/key.html

[laurena_americana]

okay... i understand the double replacement, but not the single replacement.

here is an example:
Mg(s) + CuSO4(aq) ---> MgSO4 (aq) + Cu(s)

my problem is in removing the spectator ions... is Mg the same on both sides b/c it has no charge on the left when it is not in a single cmpd. PLEASE HELP!!
THANKS SO MUCH!! you are all so helpful =)

[gladys]

The spectator ion is SO4(2-).

If you remove that, you get:

Mg(s) + Cu(2+)(aq) => Mg(2+)(aq) + Cu(s)

What is happening here is that Mg(s) is losing electrons and forming an ion which dissolves in the solution. The electrons are picked up by the Cu2+ ions in the solution which turn back into atoms of copper metal.