1. Nitric Acid Acts Upon Copper

2. While reading a textbook of chemistry I came upon the statement, "nitric acid acts upon copper." I was getting tired of reading such absurd stuff and I was determined to see what this meant. Copper was more or less familiar to me, for copper cents were then in use. I had seen a bottle marked nitric acid on a table in the doctor's office where I was then "doing time."

3. I did not know its peculiarities, but the spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words "act upon" meant. The statement "nitric acid acts upon copper" would be more than mere words.

4. All was still. In the interest of knowledge I was even willing to sacrifice one of the few copper cents then in my possession. I put one of them on the table, opened the bottle marked nitric acid, poured some of the liquid on the copper and prepared to make an observation. But what was this wonderful thing which I beheld?

5. The cent was already changed and it was no small change either. A green-blue liquid foamed and fumed over the cent and over the table. The air in the neighborhood of the performance became colored dark red. A great colored cloud arose. This was disagreeable and suffocating. How should I stop this?

6. I tried to get rid of the objectionable mess by picking it up and throwing it out of the window. I learned another fact. Nitric acid not only acts upon copper, but it acts upon fingers. The pain led to another unpremeditated experiment. I drew my fingers across my trousers and another fact was discovered. Nitric acid acts upon trousers.

8. Taking everything into consideration, that was the most impressive experiment and relatively probably the most costly experiment I have ever performed... It was a revelation to me. It resulted in a desire on my part to learn more about that remarkable kind of action. Plainly, the only way to learn about it was to see its results, to experiment, to work in a laboratory. Ira Remsen

9. Ira Remsen, born in New York City in 1846, was originally trained as a medical doctor but left that field to study chemistry and went on to become a leader in chemical education and research and to become the president of Johns Hopkins University. He was the accidental discoverer of saccharin, an artificial sweetener.

10. The nitric acid itself is dangerous. The brown gas is toxic.

11. Use a fume hood! The brown gas is toxic.

12. Now you are going to see how nitric acid acts upon copper. Several copper pennies will be placed into a solution of concentrated nitric acid. What is the formula for nitric acid? HNO 3

13. The 18M stock solution of nitric acid. A 4M solution of nitric acid. Copper pennies.

14. The pennies are placed into a beaker of nitric acid, HNO 3, in a fume hood. A watch glass makes the gas more visible.

15. Check out the temperature change. What changes do you observe in the liquid?

16. This sample went from 22C to 38C.

17. The reaction is stopped by removing the pennies.. What changes do you observe in the pennies?

18. How has the liquid phase changed? With what acids will copper react? What accounts for the color?

19. The pennies used must have been minted before 1982. Why?

20. Cu(s) + HNO 3 (aq) State symbols (s) = solid (l) = liquid (g) = gas (aq) = aqueous solution HNO 3 has a definite composition. Copper, Cu, is an element. HNO 3 is a compound called nitric acid. When it is dissolved in water, it forms an aqueous solution.

21. Cu(s) + HNO 3 (aq) When nitric acid, HNO 3, is dissolved in water, it separates completely into ions. What are ions? Ions are charged atoms or groups of atoms. They have a charge because they have gained or lost electrons. In aqueous solution HNO 3 exits as separate hydrogen ions, H +, and nitrate ions, NO 3 -.

22. When nitric acid, HNO 3, reacts with copper metal, copper ions, Cu 2+ are formed. In addition, nitrogen monoxide gas, NO, is formed, along with liquid water. The equation begins to look like this: Cu(s) + HNO 3 (aq) Cu(NO 3 ) 2 (aq) + NO(g) + H 2 O(l) Products Reactants

23. Cu(NO 3 ) 2 (aq) + NO(g) + H 2 O(l) Cu(s) + HNO 3 (aq) Cu(NO 3 ) 2 is called copper(II) nitrate. The soluble salt exists as copper ions, Cu 2+ and nitrate ions, NO 3 -, in aqueous solution. How do we detect the presence of ions? The light bulb conductivity tester lights up when ions conduct electricity.

24. Cu(NO 3 ) 2 (aq) + NO(g) + H 2 O(l) Cu(s) + HNO 3 (aq) Demo: 1.Test conductivity of pure water. 2.Add nitric acid to pure water. 3.Dissolve solid Cu(NO 3 ) 2 in pure water.

25. Cu(NO 3 ) 2 (aq) + NO(g) + H 2 O(l) Cu(s) + HNO 3 (aq) There is something wrong with this chemical equation. It isn’t balanced. The law of conservation of matter (or mass) says that every atom must be accounted for. Adjust the coefficients to even up the atoms. Hint: A 3 goes there. 3

26. Cu(NO 3 ) 2 (aq) + NO(g) + H 2 O(l) Cu(s) + HNO 3 (aq) There is something wrong with this chemical equation. It isn’t balanced. The law of conservation of matter (or mass) says that every atom must be accounted for. Adjust the coefficients to even up the atoms. Hint: A 3 goes there. 3 Come, come. Balance the equation before going on.

27. 38824 3Cu(NO 3 ) 2 (aq) + 2NO(g) + 4H 2 O(l) Cu(s) + 8HNO 3 (aq) When the equation is balanced, these will be the coefficients. 3 38824 CuHNOReactantsProducts Count the atoms

28. 3Cu(NO 3 ) 2 (aq) + 2NO(g) + 4H 2 O(l) What are some indications that a chemical reaction has taken place? 3Cu(s) + 8HNO 3 (aq) 1.A gas is given off 2.A color change occurs 3.A temperature change occurs A fourth indicator of a chemical reaction didn’t occur here. It is the formation of an insoluble precipitate.

29. 3Cu(NO 3 ) 2 (aq) + 2NO(g) + 4H 2 O(l) We saw the temperature of the solution increase. Was energy absorbed or released by this reaction? 3Cu(s) + 8HNO 3 (aq) Energy was given off in the reaction, which accounted for the rise in temperature. Reactions that give off energy are exothermic. Reactions that absorb energy are endothermic.

30. 3Cu(NO 3 ) 2 (aq) + 2NO(g) + 4H 2 O(l) This is called a “molecular equation” because everything is written as molecules, but it doesn’t take into account that some substances exist as ions in aqueous solution. 3Cu(s) + 8HNO 3 (aq) A better way to write is as an ionic equation.

31. 3Cu(NO 3 ) 2 (aq) + 2NO(g) + 4H 2 O(l) 3Cu(s) + 8HNO 3 (aq) 3Cu 2+ + 6NO 3 - + 2NO(g) + 4H 2 O(l) 3Cu(s) + 8H + + 8NO 3 - Now, everything that exists as an ion, is written as an ion.

32. 3Cu 2+ + 6NO 3 - + 2NO(g) + 4H 2 O(l) 3Cu(s) + 8H + + 8NO 3 - But NO gas is a colorless gas. Where does the brown gas come from? The reaction is between the atoms of copper and the nitrate ion. This produces copper ions and NO gas.

33. And NO 2 is a reddish-brown, vile smelling, somewhat toxic gas. There is a “side-reaction”, in which NO gas reacts with the oxygen gas, O 2, in the air to make NO 2. 2NO(g) + O 2 (g) 2NO 2 (g)

34. 3Cu 2+ + 6NO 3 - + 2NO(g) + 4H 2 O(l) 3Cu(s) + 8H + + 8NO 3 - This is the first reaction in a series of reactions that you will be doing in a lab called the “Copper Cycle”.

35. No, not that kind of cycle.

36. The Copper Cycle

37. A series of reactions involving copper where the reactants in one step are the products from the previous step.

38. Copper Lab Balancing Equations Evidence of reaction Types of reactions Predicting products Acid/base neutralization Net ionic equations REDOX Reaction rate factors pH and [H + ] Stoichiometry Activity series Solubility rules Acids Stock system Nomenclature 1. Precipitate 2. Gas given off 3. Temperature change 4. Color change 1. Synthesis 2. Decomposition 3. Single replacement 4. Double replacement 5. Combustion of a hydrocarbon 1. Concentration 2. Temperature 3. Surface area 4. Catalyst Thermodynamic s Endothermic & exothermic Reaction pathway diagrams Activation energy Oxidizing and reducing agents Strong & weak The Copper Cycle Lab

39. Comments or questions may be directed to Mike Jones Pisgah High School Canton NC mjones@haywood.k12.nc.us 07/13/05 06/02/10 Rev. 011812