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Home Q & A Board Science-Related Homework Help Chemistry (Moderator: Laser_3)
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dauterjudy938 dauterjudy938
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12 years ago
I don't understand this at all..could someone please help me?

Mg(s)+Cr3+(aq)->Mg2+(aq)+Cr(s)

and this one...

Al(s)+Ag+(aq)->Al3+(aq)+Ag(s)

they already look balanced to me but they aren't cause I got it wrong on my first try!

Please help me!
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#1
12 years ago
Redox reactions: Short for Reduction-Oxidation reactions.

That means that the electrical state of molecules are changing.

To balance it, you have to using half-reactions.
LEO says GER

Loss of Electrons is Oxidation.
Gain of Electrons is Reduction.

or

OIL RIG
Oxidation is Loss.
Reduction is Gain.

You break the equation into the oxidation and reduction halves. Then you balance the electrons. You'll need the help of protons. Then you have to balance the protons with water. Put the reaction together.

Pull out your chemistry textbook, and I bet you can do this easy!
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#2
12 years ago
They are not balanced equation.
A balanced equation is an equation that is balanced in a) the number of atoms and b) the charge on both side of the equation.

Your equation only satisfies the first condition.

This is how to do it:

a) Write the half equations. ( there are two half-equations).
b) Balance the half equation in terms of number of atoms and charge.( the number of electrons)
c) Add the two balanced half-equations as to get rid of the electrons.  
    The final balanced equation should not have any electrons.

So, for the first equation:

Mg(s)  --------------------> Mg2+(aq)  + 2e  ................(1)

Cr3+(aq)  +  3e -------> Cr(s)  ............................. ....(2)

(1) x  3 =>  3Mg(s) ----------------> 3Mg2+(aq) + 6e ......(3)
(2) x 2  =>  2Cr3+(aq)  + 6e ---> 2Cr(s) .....................(4)

(3) + (4) =>  3Mg(s) + 2Cr3+(aq) -----> 3Mg2+(aq) + 2Cr(s)

You can try the second equation on your own.
Just follows the same procedures. Good luck!
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