# IB DP Chemistry: SL复习笔记1.2.2 Reaction Yields

### Reaction Yields

#### Percentage yield

• In a lot of reactions, not all reactants react to form products which can be due to several factors:
• Other reactions take place simultaneously
• The reaction does not go to completion
• Products are lost during separation and purification
• The percentage yield shows how much of a particular product you get from the reactants compared to the maximum theoretical amount that you can get: • The actual yield is the number of moles or mass of product obtained experimentally
• The theoretical yield is the number of moles or mass obtained by a reacting mass calculation

#### Worked Example

In an experiment to displace copper from copper(II)sulfate, 6.5 g of zinc was added to an excess of copper(II)sulfate solution.The resulting copper was filtered off, washed and dried.The mass of copper obtained was 4.8 g.Calculate the percentage yield of copper.

Step 1: The symbol equation is:

Zn (s)+CuSO4 (aq)→ZnSO4 (aq)+ Cu (s)

Step 2: Calculate the amount of zinc reacted in moles Step 3: Calculate the maximum amount of copper that could be formed from the molar ratio:

Since the ratio of Zn(s) to Cu(s) is 1:1 a maximum of 0.10 moles can be produced

Step 4: Calculate the maximum mass of copper that could be formed (theoretical yield)

mass=molxM=0.10molx63.55g mol-1=6.4 g (2 sig figs)

Step 5: Calculate the percentage yield of copper  