Percent Yield Calculator

In short Percent yield is the actual mass you recovered divided by the theoretical maximum, times a hundred. Recovering 20 g where 25 g was possible is an 80% yield. The theoretical yield comes from the limiting reagent — whichever reactant runs out first, which is not necessarily the one you weighed most carefully. Convert its mass to moles, apply the mole ratio from the balanced equation, and convert back to the mass of product: heating 10 g of calcium carbonate, 100.09 g/mol, to give calcium oxide at 56.08 g/mol in a one-to-one reaction can give at most 5.6029 g, whatever you do. To find the limiting reagent when there are several, divide each reactant's moles by its coefficient in the balanced equation and take the smallest quotient. A yield above 100% is not a good result; it is a wet product. Atoms do not appear, so mass cannot exceed the theoretical maximum, and a figure over 100% means residual solvent, water, or unreacted starting material is being weighed as product. Dry to constant mass and weigh again. At the other end, a low yield in a teaching lab is more often mechanical than chemical: transfer losses, material left on the filter paper and in the flask, and recrystallisation are usually bigger than any side reaction. Below about 50% it is worth asking where the material physically went before concluding the reaction failed. Finally, percent yield says nothing at all about purity. A 95% yield of a contaminated solid is a worse result than a 60% yield of clean material, and only an analysis will tell the two apart.