IB DP Chemistry: HL复习笔记1.2.2 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

Answer:

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 =   mol  x  M

                                    =   0.10 mol x 63.55 g mol^-1

                     =   6.4 g (2 sig figs)Step 5: Calculate the percentage yield of copper