Question

1. Which of the major physical laws of chemistry are you testing when you calculate the pencent recovery? Explain.

2. The mass of recovered copper may be measure greater or less than the amount at the beginning.

     2a). Give at least one reason why the mass of recovered copper might be greater than the initial mass of copper, and one reason why it might be less than the initial mass.

    3b). What steps could be taken to minimize these sources of error in the experiment.

3. In this experiment, reactions 1, 6 and 7 are of the same classification. What type of reaction do they represent? Explain your choice by writing one of the reaction equations and identifying the reactants according to their behavior.

4. Show by calculation that the 2.0 g of zinc used in reaction 6 is enough to completely react with the mass of copper that you started with.

5. The State of Liberty is made of bronze, but exhibits a green surface, or "patina". What is bronze? Based on the composition of bronze, suggest a chemical reason for the green color and write a chemical reaction to illustrate.

Answer 1

1. Percent recovery is based mainly on law of conservation of mass, which derivates from:

this states that --> initial amount of reagents = final amount of products

therefore, we can pre-calcualte the theoretical amount, which then is related to the yield

if this wouldnt be constant, we could calculate yield

Q2

a) if mass is greater, the experiment was probably done incorrect, for instance, this is not actually pure copper, but contains impurities or copper oxides, which will have higher mass than pure copper

b)

we can minimize this if we ensure purityt of Copper via other procedures