I have a question about balancing equations.?

Question

For example, to write a balanced (single replacement) equation for:

Zn + AgNO[sbscrpt3] ---> ?

I would have simply written

Zn + AgNO[sbscrpt3] ---> ZnNO[sbscrpt3] + Ag

However, the book lists the answer as


Zn + 2Ag(NO[sbscrpt3])[sbscrpt2] ---> Zn(NO[sbscrpt3])[sbscrpt2] + 2Ag

Why?

Is it because the O is diatomic, so you need to add:


Zn + AgNO[sbscrpt3] ---> Zn(NO[sbscrpt3])[SBSCRPT2 HERE] + Ag

Thus needing to add:

Zn + [COEFFICIENT 2 HERE]AgNO[sbscrpt3] ---> Zn(NO[sbscrpt3])[sbscrpt2] + Ag

And finally:

Zn + [coefficent2]AgNO[sbscrpt3] ---> Zn(NO[sbscrpt3])[sbscrpt2] + [COEFFICIENT 2 HERE]Ag


?

Also, how did the subscript 2 get added to just the (NO[sbscrpt3]) ... as in ZnNO[sbscrpt3]? I thought you couldn't add subscripts that weren't there to begin with so you'd have to make that whole part 2ZnNO[sbscrpt3], and add a 2 as the coefficent in the lone Zn on the left side of the equation?

Thanks a bunch!

Wait wait wait. I think I just figured it out again.

On the right side of the equation, when the Zn and NO[sbscrpt3] are paired together, there needs to be 2 NO[sbscrpt3]'s because it has a 1- charge and the Zn had a 2+ charge. Right? Is that how that whole thing was done? Because if so, then the rest just falls into place and I get how to do it. :)

Yay! Thanks for your super quick replies. I'm so glad that I get it now!!!! :)))))))))))))))

Answer 1

The reason your equation is wrong is because Zn makes a 2+ ion while Ag is a 1+ here (NO3 is a 1-, by definition).

(NO3)-1 must be doubled in order to balance the 2+ Zn ion.

Hope that simplifies it for you.

Answer 2

You need to know the charges of the ions that are formed and thus how to combine them to get species with no charge. it has nothing to do with the oxygen.

Zinc forms a +2 ion preferentially, because it can adopt a pseudo-noble gas configuration by losing its 2 4s electrons and going to an [Ar]3d10 configuration. Similarly, silver forms a +1 ion to get to the same type of configuration.

Nitrate on the other hand is a -1 anion.

So, in the reaction you're seeing, silver is being reduced from its +1 ion to the neutral metal, while zinc is being oxidized from the metal to the +2 ion (nitrate is really just a spectator here). In order for that to work, you have to have 2 silvers for every zinc, and the nitrate will be there to balance out the charges.

Thus, it is:

Zn + 2 AgNO3 ---> 2 Ag + Zn(NO3)2

Answer 3

When u add Zn to AgNO(3) , always keep in mind tht Zn has a charge of 2+ and NO(3) has -1.... So it will always be the charge which goes to the suffix of its neighbouring atoms or ion ..