S4.7.4 For the adult
Reacting masses and yield
If I burn 12 g of magnesium, how much magnesium oxide can I make?
What this chapter teaches
The numbers in a balanced equation are moles. To find a mass of product, change the mass you know into moles, use the equation ratio, and change the moles back into mass. Percentage yield is the actual yield divided by the theoretical yield, times 100, and it is below 100 because some product is lost or another reaction takes place.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why does 12 g of magnesium make 20 g of magnesium oxide?
- What are the three steps for finding the mass of a product?
- What are two reasons why a real yield is smaller than the theoretical yield?
After the chapter, the learner can
- Calculate the mass of product from a given mass of reactant
- Calculate percentage yield and explain why it is below 100
What they copy into their notebook
Numbers in an equation are moles. Mass to moles with Mr, moles to moles with the ratio, moles to mass with Mr. Percentage yield = actual ÷ theoretical × 100.