Okay, so I'm wondering if any Chemistry boffins could possibly help me with my homework. I'm working on Mole calculations with the formula n=m/M (n being moles, m being mass (in grams), and M being Molar Mass), and I'm struggling with some homework questions we've been given.

I'll write it out exactly as I have it on my sheet. It's set out in steps that I should do it in.

"Cu + 2AgNO₃ -> Cu(NO₃)₂ +2Ag
What mass of Cu should be added to silver nitrate solution to precipitate exactly 1.00g of silver?
1. Calculate n(Ag) in 1.00g of silver.
M(Ag) = 107.9gmol^-1

2. Calculate n(Cu) required.

3. Calculate m(Cu) required. M(Cu) = 63.5gmol^-1"

I've hokerd out the first step by using n=m/M, and I came out with 9.267840593x10^-3, or 0.009mol. I just don't understand how I'm supposed to work out the next step. I've tried a few things, but I'm not confident AT ALL in those methods

Any help at all is greatly appreciated. Thanks!

Well, 1 mole of copper gives 2 mole silver. so how many moles copper gives 0.009 mole silver?

then how many grams would that number of moles weigh?

Pretty much what Rhomphaia said, I just wanted to let you know that your verbiage made me chuckle.

Ah, okay, thank you! I haven't quite got the answer yet, but that makes it a lot clearer. Thanks again!

While this one is fairly easy, it's important to properly set up a chemistry problem so that you can follow the same steps when it gets harder. Knowing how to go from grams, to moles, (and why you need to do so), then using the stoichiometric ratio to go from moles of one product/reactant to another, to grams.

So, it would look like:

1gAg / 1 * 1molAg / (107.8682g/mol) * 1molCu / 2molAg * 63.546gCu / 1molCu = gCu needed.

mass of silver -> moles of silver -> moles of copper, which just uses the stoichiometric ratio (co-efficient of what you want over co-efficient of what you have), which in this case is just dividing by 2, but it's good to know how to set it up. This only relates moles to moles, which is why the first step is to convert to moles -> grams of Cu

So for 1, you would stop after using the stoichiometric ratio, and for 2, you would just do the last step.

Yeah, my teacher explained it a little more today. I completely forgot about ratios Thanks heaps though! I really appreciate it