Percentage yield: where did my product go?

4 minAS Level2.4.1

AI-drafted, independently checked · not yet teacher-reviewed

By the end of this lesson

By the end you can calculate a percentage yield, explain why it is usually below 100%, and work backwards to find how much reactant you need for a target mass of product.

The recipe said 12 cookies

The recipe promised 12 cookies. You got 9: two welded themselves to the tray and one "fell" into your mouth. Chemistry has the same heartbreak, with numbers.

Theoretical yield: the mass of product you should get, calculated from the equation, assuming the reaction goes to completion with no losses.
Actual yield: the mass you really get, weighed at the end.

Definition

Percentage yield

$\text{percentage yield} = \frac{\text{actual yield}}{\text{theoretical yield}} \times 100\%$

Both yields must be in the same units (usually grams, or both in moles).

Worked example: Making a fruity ester

6.00 g of ethanoic acid is heated with excess ethanol and a little concentrated sulfuric acid: $\text{CH}_3\text{COOH(l)} + \text{CH}_3\text{CH}_2\text{OH(l)} \rightleftharpoons \text{CH}_3\text{COOCH}_2\text{CH}_3\text{(l)} + \text{H}_2\text{O(l)}$ The student collects 5.72 g of pure ethyl ethanoate. Calculate the percentage yield. ( $M_r$ : ethanoic acid 60.0, ethyl ethanoate 88.0)

Have a go first?

Quick check

Fill in the blanksQuestion 1 · Recall

CalculateQuestion 2 · Apply

Answer the 2 questions above to continue.