REVIEW OF THEORETICAL YIELD CALCULATIONS
Based on the quantities of reactants you use in a chemical reaction,
calculate the grams of product you can theoretically make. Then calculate
"Percent Yield."
IF you know that one of two reactants is in "EXCESS", then focus on the
calculation involving the other reactant – it will be used up first. If you do not
know which reactant is limiting, do the following:
Calculate TWO scenarios, one for each reactant. The scenario that
gives the LEAST amount of product is the limiting reactant; use this
result and ignore the other scenario.
The calculation of yield will follow the pattern of
1) mass of reactant to mole of reactant
2) mole of reactant to mole of desired product
3) mole of product to mass of product
Example:
Given the following reaction of methane with oxygen, determine the
theoretical yield of water if you have 24.0 gram CH4 and 48.0 gram O2.
CH4 + 2 O2  CO2 + 2 H2O
methane scenario:
1 mol CH4
2 mol H2O 18.0 g H2O
24.0 g CH4 (----------------) ( --------------) (----------------) = 54.0 g H2O
16.0 g CH4 1 mole CH4
1 mol H2O
oxygen scenario:
1 mol O2
2 mol H2O 18.0 g H2O
48.0 g O2 ( ------------) ( -------------- ) ( --------------) = 27.0 g
32.0 g O2
2 mol O2
1 mol H2O
Since the oxygen scenario gave the least amount of product, the O2 is
limiting and this is the correct calculation. Theoretical yield is 27.0 g H2O.
DISCUSSION CONTINUED ON OTHER SIDE
continued
• Use the actual amounts weighed out in lab, not the amount you planned
to use. Your notebook must show your yield calculation.
• Note that you must start with gram quantities. If starting with a volume of
reactant, use its density to covert to grams.
Percent Yield is (actual grams / theoretical grams) X 100%
SUBMITTING AND LABELING YOUR PRODUCT
If the lab preparation involved creating a product, it must be placed in a
capped jar or bottle, labelled, and submitted to the instructor. Do not make
the mistake of weighing the bottle once with the lid and once without.
The label MUST contain the following: (example at bottom of page)
your name
official name of chemical
melting point (mp) or boiling point (bp) range
gram yield
percent yield
It is understood that you may have removed a small portion of sample for
testing. While this will lower the quantity of sample submitted, your label
should reflect the total mass of sample you prepared prior to testing. Note
that if for some reason you removed a large portion of sample, inform the
instructor. Why? Because the instructor will occasionally weigh the product
you submit or test it to see if your reported values are correct. If your
sample is not immediately ready for submission, you will have to complete
it by the due date by working on it the next lab or arranging with the
instructor to enter the lab on another day.
sample label
Stu D. Ent
acetylsalicylic acid
mp = 132 - 134 C
1.37 g yield
43 % yield