A Series of Chemical Reactions Involving Copper

The objective of this lab is to demonstrate a sequential series of chemical reactions involving copper and its common compounds. Through these reactions, students will gain a deeper understanding of electrons in atoms, chemical bonding, chemical reactions and quantities, molecules, compounds, and chemical composition. The lab also emphasizes the proper use of exponential notation, significant figures, and safe laboratory practices.

The discussion introduces the five equations that describe the reactions involving copper:

1. Copper reacts with concentrated nitric acid to form copper nitrate, water, and nitrogen dioxide.

2. Copper nitrate reacts with sodium hydroxide to form copper hydroxide and sodium nitrate.

3. Copper hydroxide is heated to produce copper(II) oxide and water.

4. Copper(II) oxide reacts with sulfuric acid to form copper(II) sulfate and water.

5. Copper sulfate reacts with metallic zinc to produce metallic copper and zinc sulfate. The second part of equation 5 shows the production of gaseous hydrogen.

The lab procedure begins with obtaining a sample of copper and adding concentrated nitric acid to dissolve it. It is important to handle the concentrated nitric acid with care due to the production of toxic fumes. After adding water and sodium hydroxide solution, the solution is stirred until it becomes basic. The addition of water and gentle boiling with stirring follows, causing the blue color to disappear or darken. The resulting solution is then filtered, and the solid copper hydroxide is collected.

To convert the copper hydroxide to copper(II) oxide, dilute sulfuric acid is poured through the filter multiple times. The solid is washed with water, and all the solutions are combined. Next, a piece of metallic zinc is added to the solution, resulting in the formation of metallic copper and the evolution of hydrogen gas.

In the notebook, students are instructed to write a brief statement about each step in the sequence of chemical reactions, including the equations. They should also indicate the color of all solutions and solid precipitates.

This lab allows students to observe and understand the transformation of copper from its metallic form to various compounds and back to metallic copper again. It reinforces concepts related to electron configurations, chemical reactions, stoichiometry, and the composition of matter and energy. Students will develop skills in using laboratory tools and equipment, practicing safe procedures, recording experimental results, and applying scientific reasoning to evaluate phenomena.

Objective

· Use the tools and equipment necessary for basic scientific analysis and research

· Demonstrate safe practices in the Chemical Laboratory

· Demonstrate an understanding of Electrons in Atoms and the Periodic Table and Chemical Bonding

· Demonstrate an understanding of Chemical Reaction and Quantities in Chemical Reactions

· Demonstrate an understanding of Molecules, Compounds and Chemical Composition

· Demonstrate the proper use of Exponential Notation and Significant Figures

· Demonstrate an understanding of the composition of matter and energy

· Record the results of investigation through writing

· Use scientific reasoning to evaluate physical and natural phenomena

· Identify the unifying themes of the scientific field of study

Materials

· Copper

· Beaker

· Concentrated Nitric Acid

· Watch Glass

· 6M Sodium Hydroxide

· Glass Stir Rod

· Litmus Paper

· Hot Plate

· Liquid Funnel

· Filter Paper

· 3M Sulfuric Acid

· Metallic Zinc

Discussion

In this experiment, a fascinating sequence of chemical reactions is conducted to transform metallic copper into several of its typical compounds, ultimately leading back to copper itself. The reactions are outlined by the following five equations, depicting the transformation process of copper.

(1) Cu + 4HNO3 → Cu(NO3)2 + 2H2O + 2NO2

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

(3) Cu(OH)2 (HEAT)→ CuO + H2O

(4) CuO + H2SO4 → CuSO4 + H2O

(5)

a. CuSO4 + Zn → Cu + ZnSO4

b. Zn + H2SO4 → ZnSO4 + H2

Equation (1) illustrates the process of solid copper dissolving in concentrated nitric acid to produce a liquid solution. Although the substances are denoted as molecules in the equation, the actual entities present in the solution are the ions of the compounds. Equation (2) demonstrates the precipitation of copper ions as insoluble Cu(OH)2. Generally, the formation of insoluble precipitates promotes the completion of reactions, pushing them towards the right side as indicated by the reaction.

Following filtration, the conversion of the solid Cu(OH)2 into a different copper compound, CuO, takes place in reaction 3 by applying heat to eliminate water. Equation 4 describes the dissolution of CuO with sulfuric acid. Finally, equation 5a signifies the conversion of copper into its metallic form. Equation 5b is included to illustrate the experimental observation of gaseous hydrogen production.

Procedure

1. Obtain approximately 1-1.5g of copper and place it in a 400 ml beaker. In a fume hood, add 5 mL of concentrated nitric acid to the beaker (handle with care). Immediately cover the beaker with a watch glass and let it sit until all the copper dissolves. Once the fumes have dissipated, remove the watch glass and bring the beaker to your desk. Add 15 mL of distilled water.

a. Note: Concentrated nitric acid produces brown toxic fumes (NO2) when mixed with water. Avoid contact and inhalation of the fumes as they are extremely poisonous.

2. While stirring, cautiously add 10 mL of 6 M sodium hydroxide solution. Test the solution with litmus paper. If it is not basic (red litmus does not turn blue), add small portions of sodium hydroxide until the solution is basic to litmus.

3. Add 50 mL of water to the solution. Gently bring it to a boil while stirring constantly to prevent bubbling. Continue boiling until the blue color disappears or darkens. Filter the hot solution and discard the colorless liquid (filtrate). Rinse all the solid from the beaker onto the filter, then wash the solid with additional water and discard the wash water.

4. Using a wire, create a small hole in the bottom of the filter paper. Pour 10 mL of 3 M dilute sulfuric acid through the filter, collecting the solution in a flask or beaker. Pour the same solution back through the filter, collecting it as before. Repeat this process until all the solid has dissolved. Rinse the filter paper with small portions (5 mL) of water and combine all the solutions.

5. Introduce a piece of metallic zinc into the solution obtained from step 4 and stir it using a glass rod. Observe the formation of metallic copper and the evolution of hydrogen gas.

6. In your notebook, write a concise statement for each step, including relevant equations, to describe the sequence of chemical reactions. Maintain neatness and orderliness. Also, indicate the color of all solutions and solid precipitates.

Questions for A SERIES of CHEMICAL REACTIONS INVOLVING COPPER

Name_______________________________________ Date___________________________

Lab / Section_________________________________

1. Name the starting product for this experiment.

2. When performing this lab experiment, the first step is to be done under the hood. Which chemical are you adding to your wire?

a. NaOH

b. HNO3

c. H2SO4

3. While heating the Cu(OH)2 it is necessary to stir CONSTANTLY. True / False

4. Why do you think the reason is to add NaOH?

a. To make the solution neutral

b. To make the solution basic

c. To make the solution acidic

Review Questions

1. What is the objective of the lab?

_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

2. What tools and equipment are necessary for the lab?

3. How can safe practices be demonstrated in the chemical laboratory?

4. Explain the concept of electrons in atoms and its relevance to the lab.

5. What is the periodic table and how is it related to chemical bonding?

6. Describe the chemical reactions involved in the lab and their corresponding equations.

7. How is the empirical formula of a compound determined?

8. Why is it important to use exponential notation and significant figures in scientific calculations?

9. How can the results of an investigation be recorded through writing?

10. Give an example of using scientific reasoning to evaluate a physical or natural phenomenon in the lab.

11. What are the unifying themes of the scientific field of study relevant to this lab?

12. Explain the process of decantation and its application in the lab.

13. What is the purpose of filtration and how does it separate substances?

14. Describe the coagulation process and its significance in water treatment plants.

15. How does distillation work as a purification technique?

16. When is extraction used and how does it separate components of a solution?

17. What is sublimation and how can it be used to separate solids?

18. What is the law of definite proportions and how does it relate to Dalton's atomic theory?

19. How does the composition of matter and energy play a role in the lab?

20. Provide an overview of the lab procedure and explain the significance of each step.

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