PERCENT YIELD!!

Sometimes, it is not possible to recover all the product, or not all the reactions are used up, and therefore, we need to calculate PERCENT YIELD.

PERCENT YIELD=the ratio of amount of product obtained to amount of product expected by claculated, expressed as a %.

% YIELD=grams of actual product recovered/grams of product expected from stoich×100%

ex. HBrO3+5HBr→3H2O+3Br
if 10.0g of HBrO3 is reacted with excess HBr and 26.3g of Br2 was prodeced, what is the percent yield?
10×(1mole/128.9g)×(3mole/1mole)×(159.8g/1mole)=37.191g Br2

%YIELD=26.3g/37.191g×100%=70.7% yield

ex. C3H6Cl2+2KSCN→C3H6(SCN)2+2KCl
the % yield is 80%.  how many grams of C3H6(SCN)2 will be produced if 3.00 grams of C3H6Cl2 is reacted with excess KSCN?
3g×(1mole/113g)×(1mole/1mole)×(158g/1mole)=4.20g C3H6(SCN)2

% YIELD=C3H6(SCN)2 obtained/420g expected×100%=80.0% yield
C3H6(SCN)2=3.36g