Phalanges - 31-10-2011 at 13:46
Hello,
I'm looking for some help in predicting an reaction, or more accurately figuring out my theoretical yield.
If I've got 15.0g of MgSO4 and 10.0 g of Pb(NO3)2, how would I calculate the theoretical yield?
I'm not looking for the numerical answer, I'm more of trying to figure out the process. Any help would be greatly appreciated! Thanks in advance!
[Edited on 31-10-2011 by Phalanges]
[Edited on 31-10-2011 by Phalanges]
stygian - 31-10-2011 at 13:58
Use the molecular weights to figure out moles of reactants and products. stoichiometry its called
Mr. Wizard - 31-10-2011 at 14:43
This may be too much detail, but here goes.
Looking at the equation, you can see one molecule of Magnesium Sulfate reacts with one molecule of Plumbic (Lead) Nitrate.
The numbers of molecules react on a 1:1 ratio. How many molecules are in 15 grams of MgSO4?
Add up the Atomic Weights from a Periodic Chart
I'm going to use rounded off numbers, but you should use the actual average number.
Mg=24
S= 32
O=16
O=16
O=16
O=16
Total=120 So when you have 120 grams of that substance you have one Mole or Avogadro's Number = 6.022 x 10^23 molecules.
Since you only have 15 grams you only have
15/120 x 6.022x10^23 molecules or .125 of a Mole
Lead Nitrate
Pb=207
N=14
N=14
O=16
O=16
O=16
O=16
O=16
O=16
Total=331 grams to make a Mole
Since we have only 10 grams we have
10/331 = .03 mole of Lead Nitrate
Since there has to be an equal number of molecules reacting from both sources, the Lead Nitrate will run out and be the limiting ingredient in the
final mix of PbSO4 (.03 Mole) Mg(NO3)2 (.03 Mole) and MgSO4 ( .125 -.03 Mole )
The Lead Sulfate will drop out of solution as it is very insoluble compared to the others. This is only a very basic explanation, ignoring many fine
points, and the water of hydration involved in these salts.
I sure hope I added those up right
Bot0nist - 1-11-2011 at 05:56
Thanks for that excellent explanation Mr. Wizard. Unit conversion factors and stoichiometry are some of the boring bits of chemistry, but they are
invaluable, and once you learn them it makes everything a lot easier. Take the time now to learn and practice. Cause once you know its "like riding a
bike."
Here is another good and simple work through.
<a href="http://www.cavemanchemistry.com/oldcave/projects/stoich/index.html">Stoichiometry</a>
Good luck!
[Edited on 1-11-2011 by Bot0nist]
Phalanges - 2-11-2011 at 12:57
Thanks everyone for all of your help! It finally "clicked"! 
Mr. Wizard - 2-11-2011 at 14:59
Getting that 'click' or magic moment when things make sense is the greatest.