Determination of an Empirical Formula

Introduction:

In this lab you will react copper with nitric acid to form a copper nitrate (in aqueous solution). You will then heat the solution to evaporate the water. Further heating will then decompose the copper nitrate into a copper oxide. The purpose of this lab is to determine the simplest formula of the copper oxide that is formed.

I. Purpose: The purpose of this lab is to determine the simplest formula of an oxide of copper formed by reacting copper with nitric acid to form a copper nitrate which is then heated to form either copper(I) oxide or copper(II) oxide.

II. Procedure: GOGGLES MUST BE WORN AT ALL TIMES! NITRIC ACID IS VERY DESTRUCTIVE TO HUMAN TISSUE.

1. Obtain the mass of a 15-20 cm piece of 22 gauge copper wire. Also obtain the mass of an evaporating dish.

2. Coil the copper wire so that it sits flat in the bottom of the evaporating dish.

3. Using a ring stand assembly, position the evaporating dish so that it is directly underneath one of the fume hoods.

4. Add only enough 8M nitric acid to completely cover the coil of copper.

5. Do not proceed to the next step until the solid copper is completely gone. Add more nitric acid as needed until all of the solid copper has completely reacted.

6. Light your Bunsen burner but do not bring it near the evaporating dish yet. Adjust the air intake to maximum so that you have a very hot flame.

7. Read Carefully: Holding the Bunsen burner with your hand, position the hottest part of the flame under the evaporating dish for 2-3 seconds until the liquid starts to give off steam or other visible fumes appear, then immediately remove the flame until the fuming stops. In this manner, continue to heat the evaporating dish a few seconds at a time until the liquid is totally evaporated. Be very careful not to breathe in any of the fumes that are given off during the heating process. Any spattering indicates that you are heating too strongly.

8. Once the liquid is totally gone, strongly heat the evaporating dish until the solid in the dish is dry and has turned completely black. Be very careful not to breathe in any of the fumes that are given off during the heating process.

9. Obtain the mass of the evaporating dish and copper oxide product.

10. Clean the evaporating dish by reacting the copper oxide solid with hydrochloric acid.

IV. Calculations:

Your calculations should show how many moles of Cu reacted (which ideally should be the number of moles of Cu in the final product) and how many moles of oxygen atoms are in the final product. Is the molar ratio of Cu to O more consistent with copper(I) oxide or copper(II) oxide?

V. Conclusion:

Assuming that the only possible products are copper(I) oxide and copper(II) oxide, did this procedure result in all copper(I) oxide, all copper(II) oxide, or a mixture of copper(I) oxide and copper(II) oxide being formed? Justify your conclusion.