Lab work with given data

Chemistry 201 Laboratory- Harold Washington College

Reactions of Copper and Percent Recovery

Introduction

In Chapter 4 of your textbook, we have covered the 3 main classes of reactions in aqueous

solution: precipitation reactions, acid-base reactions, and oxidation-reduction reactions. These

can be summarized as follows:

• In Precipitation reactions: a solid product forms from aqueous reactants. The product can

be predicted by using solubility rules.

• In Acid-base neutralization reactions: an acid (proton donor) reacts with a base (proton

acceptor) to form an ionic salt and sometimes water. You can recognize this type of

reaction by the presence of an acid and base in the reactants.

• In Oxidation-reduction reactions (or redox for short): electrons are transferred between

reactants. So you will always see changes in oxidation number within this type of

reaction.

In this lab, we will be examining these reactions by carrying out a sequence of reactions

starting from metallic copper in the form of a wire. According to the Law of Mass Conservation,

covered in section 2.3 of your textbook, mass is neither created nor destroyed. So since no

copper is added or removed during the course of these reactions, you should be able to

quantitatively recover all of the copper metal you started with at the end of these reactions (if

everything goes well).

You need to carefully observe and record your observations. You should be able to

carefully describe the reactions in terms of color change (color of solution or solid forming), gas

formation (as bubbles), heat generation (change in temperature), or precipitate formation,

throughout the experiment.

At the end of the reactions series, you will collect the copper recovered and calculate the

percent recovery (% yield) of copper using this formula:

% yield = actual amount of Cu recovered x 100 %

original amount of Cu

Materials and Equipment

• Piece of copper wire (about 0.5 g)

• concentrated HNO3 (aq)

• 3.0M NaOH

• 6.0M H2SO4

• solid zinc

• 2-250 mL beakers, 400 mL beaker

• 50 mL graduated cylinder

• boiling chips

• stirring rod

• iron ring and ring stand, wire gauze,

• Bunsen burner

• evaporating dish

• electronic balance

Chemistry 201 Laboratory- Harold Washington College

SAFETY NOTES

• Safety goggles should be worn at all times

• Sulfuric acid, nitric acid, and sodium hydroxide are corrosive chemicals and should be

handled with care.

• Gloves are to be worn when handling these chemicals.

• Waste should be put in the designated container in the hood. Never throw chemicals

down the drain.

PROCEDURE 1. Obtain a piece copper wire, measure its mass to the nearest 0.01 g, and place it in a 400

mL beaker.

2. IN THE HOOD, add 4-5 mL of concentrated nitric acid, HNO3, to the beaker. (Caution: Be careful not to get any of the nitric acid on yourself. If you do, wash it off

immediately with copious amounts of water. The gas produced in this reaction is

toxic, and the reaction must be performed in the hood).

This procedure is presented by the following chemical reaction:

Cu(s) + 4HNO3(aq) → Cu(NO3)2 (aq) + 2 NO2 (g) + 2 H2O(l)

What type of chemical reaction is this? ________________________

Describe the reaction as to color change, evolution of gas, and the qualitative change in

temperature. (In the data sheet)

3. After the reaction is complete (all the Cu has reacted and no more gas is given off), add 100 mL of deionized water and stir. Slowly add 30 mL of 3.0 M NaOH to the solution in

the beaker.

Describe the reaction on the data page.

Note the color of the precipitate as well as the color of the solution.

What product is formed in this step? ________________

Write the chemical reaction that is described in this step:

What type of chemical reaction is this? ________________________

Chemistry 201 Laboratory- Harold Washington College

4. Add two or three boiling chips and carefully heat the beaker-while stirring with a stirring

rod – DO NOT BOIL the SOLUTION.

Describe the reaction on the data sheet.

Note the color of the precipitate as well as the color of the solution.

What product is formed in this step? _______________

Write the chemical reaction that represents this step:

What type of chemical reaction is this? __________________________

5. Allow the black solid to settle; then decant (pour off) the supernatant liquid. Add about 200 mL of very hot deionized water, stir, and allow the solid to settle once more. Decant

the supernatant liquid again.

What is the purpose of this step? _______________________________

What species does the supernatant liquid include? __________________

6. Add 15 mL of 6.0 M H2SO4 to the solid recovered in the previous step. Remove the boiling chips.

Describe the reaction on the data page.

Note the color of the precipitate as well as the color of the solution.

What product is formed in this step? ______________

Write the chemical reaction is represented in this step:

What type of chemical reaction is this? ________________________

7. IN THE HOOD, add about 2.0 g of zinc metal all at once to the beaker and stir until the supernatant liquid is colorless.

Describe the reaction on the data page.

Note the color of the precipitate as well as the color of the solution.

What product is formed in this step? ______________

Write the chemical reaction is represented in this step:

What type of chemical reaction is this? ________________________

Chemistry 201 Laboratory- Harold Washington College

8. When gas evolution becomes very slow, heat the solution gently in the hood (but DO NOT BOIL), then allow it to cool. What gas is formed in this reaction?

Write the chemical reaction that represents this gas formation:

9. When gas evolution has stopped, decant the solution and transfer the copper precipitate to a preweighed evaporating dish, and record its mass on the report sheet.

10. Wash the precipitated copper with about 5 mL of deionized water; allow it to settle; decant the solution; and repeat the process of washing, settling, and decanting three

times.

11. Dry the product in the evaporating dish using a water bath.

12. Weigh the cooled evaporating dish containing the dry copper and calculate the %

recovery of copper.

Chemistry 201 Laboratory- Harold Washington College

Pre-Lab Assignment Name : ________________________

1. Classify the following reactions according to the 3 types of chemical reactions:

a. HCl(aq) + NaOH(aq)→NaCl(aq) + H2O(l)

b. Ba(OH)2(aq) + ZnCl2(aq)→BaCl2(aq) + Zn(OH)2(s)

c. 2AgNO3(aq) + Mg(s)→Mg(NO3)2(aq) + 2Ag(s)

d. HNO3(aq) + NH3(aq)→NH4NO3(aq) + H2O(l)

e. 2Cu(s) + O2(g)→2CuO(s)

f. CaCl2(aq)+K2CO3(aq)→2KCl(aq)+CaCO3(s)

2. Calculate the maximum volume of 6 M HNO3 which would be required to react with 0.350 g

of Cu metal as shown in the initial equation (step 2)?

3.If you used 2-3 mL of 6.0 M HNO3 to dissolve the sample of Cu (0.350 g), what volume of 4.0

M NaOH would be required to neutralize the excess HNO3?

4.Solid zinc is used in the last reaction to reduce the copper in the copper (II) sulfate solution to

elemental copper. Identify 2 other metals that could be used to perform the reduction. Explain

your answer. Write a balanced chemical equation for each identified metal.

5.Based on your research, which of these metals you think would be the “greenest” metal to use?

Justify your answer using MSDS and costs effects.

Chemistry 201 Laboratory- Harold Washington College

Data and Calculations: Name:_______________________

Mass of original copper wire ____________

Mass of empty evaporating dish ____________

Mass of evaporating dish and recovered copper ____________

Mass of recovered copper ____________

Percent yield (show calculations) ____________

1. Comment on your percent yield. List 2 sources of error that could have resulted in a

percent yield of copper greater than 100%, and 2 sources of error that could have

resulted in a percent yield less than 100%?

2. Describe the reaction in step 2 as to color change, evolution of gas, and change in

temperature.

3. Write a balanced equation for the reaction in step 2.

4. What is the color of the copper (II) nitrate solution?

5. What is the color of the nitrogen dioxide gas?

6. Describe your observations of the reaction in step 3.

7. Write a balanced equation for the reaction in step 3.

Chemistry 201 Laboratory- Harold Washington College

8. What color is the copper (II) hydroxide?

9. Describe the reaction in step 4.

10. Write a balanced chemical equation for the reaction in step 4.

11. In step 5, which substances are you removing from the solid formed by washing and

decantation?

_____

12. Describe the reaction in step 6.

13. Write a balanced equation for the reaction in step 6.

14. Describe the reactions in step 7. (There are 2 reactions occurring simultaneously)

15. Write a balanced equation for the reaction producing a solid in step 7.

16. Which gas is being produced in the other reaction in step 7?

17. Write the equation for the production to this gas.

18. Which substances are you removing by washing in step 10?

Chemistry 201 Laboratory- Harold Washington College

POST LAB Questions

1. Indicate the waste products from the reactions (i.e., the products which are not used in the following steps).

2. In step 3, you were asked to add NaOH slowly since the reaction between NaOH and HNO3 is exothermic. What type of reaction is this? Write a balanced equation for this

reaction.

3. How many milliliters of 6.0 M H2SO4 are required to react with 0.80 g of CuO according to Equation in step 6? Write the chemical equation first.

4. Write the net ionic equation for the following reaction and identify the spectator ions:

Cu(NO3) 2 (aq) + 2 NaOH (aq) → Cu(OH)2 (s) + 2 NaNO3 (aq)

5. For the following redox reactions, identify the element being reduced/oxidized, and identify the oxidizing agent/reducing agent. (Hint: assign oxidation number for each

element in the equation.)

Cu(s) + 4HNO3(aq) → Cu(NO3)2 (aq) + 2 NO2 (g) + 2 H2O(l)