Starter Walt and Jesse are making a chemical product, and they need to make as much product as possible or their boss will “sack” them. I2 + P4 C10H15N C10H15NO If they use 495kg of reactant, how much product could they end up with? After they have finished they have only made 402 kg of product. Calculate this as a percentage of the amount of product that they could have made. Suggest why the yield is lower.

Learning objectives… 1.26 calculate percentage yield

Most of the substances we use every day are made from RAW MATERIALS, often through complex chemical reactions. Reactants (raw materials) Chemical reactions Products

ACTUALLY make this much % YIELD is the amount of product you actually make as a % of the amount you should theoretically make PRODUCT REACTANTS % YIELD ABOUT 75% + SHOULD make this much ACTUALLY make this much

Percentage Yield = Actual Yield (g) f x 100 The percentage yield is a way of comparing the amount of product made with the amount predicted We refer to the amount of product made as actual yield Percentage Yield = Actual Yield (g) f x 100 (%) Predicted Yield (g) 100% yield means that there is no loss of product, 0% yield means that there is no product made

Percentage Yield = Actual Yield (g) f x 100 (%) Predicted Yield (g) PERCENTAGE YIELD EXAMPLE 1 LIMESTONE (calcium carbonate) is used to make QUICKLIME (calcium oxide) for cement making RAM Ca 40 O 16 C 12 CaCO3  CaO + CO2 100  56 + 44 RFM: So, THEORETICALLY, 100 tonnes of limestone should produce 56 tonnes of quicklime. BUT the ACTUAL YIELD is only 48 tonnes So..the PERCENTAGE YIELD is: Percentage Yield = Actual Yield (g) f x 100 (%) Predicted Yield (g) 48 ÷ 56 x 100 = 87.5% Why?

Percentage Yield The percentage yield will always be less than 100%. This is because: Product can be lost in filtration, evaporation, transferring liquids heating Why is a high yield important? reducing waste using less raw material using less energy Increasing profit

Suggest two ways in which the product could be lost? Potassium iodide is reacted with lead nitrate. The expected yield is 20 g, but only 18 g was made. What is the percentage yield? Suggest two ways in which the product could be lost? A reaction produces 48 g of copper oxide, the predicted yield was 64 g. What is the percentage yield of this reaction? What is the percent yield for a reaction if you predicted the formation of 21g of C6H12 and actually recovered only 3.8g? A reaction between solid sulfur and oxygen produces sulfur dioxide. What is the percent yield for a reaction if you predicted the formation of 680g of sulphur dioxide and actually recovered only 384g? Iron is extracted from iron oxide in the Blast Furnace: Fe2O3 + 3CO → 2Fe + 3CO2 (RFM: Fe2O3=160, Fe=56) Calculate the maximum theoretical mass of iron that can be made from 100g of iron oxide. In the reaction, only 65 g of iron was made. Calculate the % yield. 90% filtration, evaporation etc 75% 18% 56.4% 70 g 92.8%

Your challenge There is a new product called WHITE which Jesse and Walt want to make (chemical name: magnesium sulphate) There are two methods of making the product. Your task is to find out which method achieves the highest yield.

Jesse and Walt’s boss is not happy. The product they have made had a low percentage yield and lots of waste products were formed. This costs money! The boss wants some explanations. 1. Explain how the percentage yield of a reaction is usually less than 100% 2. Suggest two ways in which Jesse and Walt could improve the percentage yield of their product. 3. Explain why a low atom economy costs money and is less ‘green’? 4. How could they improve the atom economy of the chemical process they are using?