Thursday
November 27, 2014

Homework Help: chemistry

Posted by Fidelia on Monday, March 5, 2007 at 5:12pm.

Please, will someone help me balance this equation? There's always one element I just can't seem to balance.

Cu+HNO3===>NO2+Cu(NO3)2+H20

Thanks for the help.

Try this.
Cu + 4HNO3 ==> 2NO2 + Cu(NO3)2 + 2H2O

You're a genius!

Do you think you could tell me how you approached solving this problem? Like, was the answer the first thing you thought of or did it just take a lot of guessing and checking?

First, I'm not a genius.
Second, I've balanced this equation so many times in my teaching career that I have it memorized. BUT, when I did it for the first time (years ago), I had a method. Do you know how to balance oxidation-reduction equations (redox)? If not I can show you how. Or if you know how, the elements changing oxidation state are these.
Cu goes from zero on the left to +2 on the right.
N goes from +5 on the left to +4 on the right (from HNO3 to NO2). Note that there are two NO3^- that stay that way to form the Cu(NO3)2 and those two NO3^- ions don't change. Post any work you have done and I can show you what to do next.

Um, I'm not sure if I know how to balance redox equations. I just have learned how to balance equations in general, I guess.

I don't understand what you mean by this:
N goes from +5 on the left to +4 on the right (from HNO3 to NO2). Note that there are two NO3^- that stay that way to form the Cu(NO3)2 and those two NO3^- ions don't change.

There is a method to follow to balance redox equations. If you have just learned how to balance equations in general, I don't think you have learned the redox method yet. To balance the equation posted earlier, the EASY way to do it is to do it with the redox method; of course it isn't so EASY if you haven't learned that method. =). The numbers to which I refer in my post refer to the change in oxidation state of Cu on the left to Cu^+2 on the right and for N on the left to N on the right. Without the redox method, balancing this equation is a hit and miss guessing game. You will see how to do it when you cover redox.

Alright, thanks. I really hope we learn redox, then.

We shall be happy to help you when that time comes.

We shall be happy to help you when that time comes.

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