How many moles of Ag will be produced from 16.0 g of Cu, assuming AgNO3 is available in excess?

Answer 1

Assuming the reaction you are referring to is the following:

AgNO₃ + Cu --> Cu(NO₃)₂ + Ag

First, we should balance the reaction:

2 AgNO₃ + Cu --> Cu(NO₃)₂ + 2 Ag

Now we carry out dimensional analysis, taking into account the molar ratios of different species as given in the balanced reaction and molar masses (which we can look up in the periodic table).

We begin with what we know, which is that we have 16.0 g Cu reacting and work our way toward the quantity that we would like to calculate, namely moles of Ag.

16.0 g Cu x 1 mol Cu x 2 mol Ag = 0.504 mol Ag

63.5 g Cu 1 mol Cu

Notice that we begin with what we know (16.0 g Cu) and then convert the quantity to moles. This is a must since the only way we can relate the quantity of Cu to Ag is through a molar ratio given in the balanced reaction. We use the molar ratio to switch between one species and the other. (Now our units are in moles of Ag, instead of Cu.) In this problem, this is what we were asked to compute, so we are finished. Oftentimes a problem will ask for grams of the second substance, in which case we just use the molar mass of the second substance to convert from moles to grams.

That's it. I hope it helps. Feel free to leave any follow-up questions in the comments and I will answer as soon as I can.