Nitric Acid Acts Upon Copper

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

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

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? HNO3

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, HNO3, in a fume hood. A watch glass makes the gas more visible.

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

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? What accounts for the color? With what acids will copper react?

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

20. Cu(s) + HNO3(aq) Copper, Cu, is an element. HNO3 is a compound called nitric acid. State symbols HNO3 has a definite composition. (s) = solid (l) = liquid (g) = gas (aq) = aqueous solution When it is dissolved in water, it forms an aqueous solution.

21. Cu(s) + HNO3(aq) When nitric acid, HNO3, is dissolved in water, it separates completely into ions. Ions are charged atoms or groups of atoms. They have a charge because they have gained or lost electrons. What are ions? In aqueous solution HNO3 exits as separate hydrogen ions, H+, and nitrate ions, NO3-.

22. Reactants Cu(s) + HNO3(aq) Products Cu(s) + HNO3(aq) When nitric acid, HNO3, reacts with copper metal, copper ions, Cu2+ are formed. In addition, nitrogen monoxide gas, NO, is formed, along with liquid water. The equation begins to look like this: Cu(NO3)2(aq) + NO(g) + H2O(l)

23. The light bulb conductivity tester lights up when ions conduct electricity. Cu(s) + HNO3(aq) Cu(NO3)2(aq) + NO(g) + H2O(l) Cu(NO3)2 is called copper(II) nitrate. The soluble salt exists as copper ions, Cu2+ and nitrate ions, NO3-, in aqueous solution. How do we detect the presence of ions?

24. Cu(s) + HNO3(aq) Cu(NO3)2(aq) + NO(g) + H2O(l) • Demo: • Test conductivity of pure water. • Add nitric acid to pure water. • Dissolve solid Cu(NO3)2 in pure water.

25. Cu(s) + HNO3(aq) 3 Cu(NO3)2(aq) + NO(g) + H2O(l) 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.

26. Cu(s) + HNO3(aq) 3 Cu(NO3)2(aq) + NO(g) + H2O(l) Come, come. Balance the equation before going on. 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.

27. Reactants Products Cu H N O Count the atoms Cu(s) + 8HNO3(aq) 3 3Cu(NO3)2(aq) + 2NO(g) + 4H2O(l) When the equation is balanced, these will be the coefficients. 3 8 8 24 3 8 8 24

28. 3Cu(s) + 8HNO3(aq) 3Cu(NO3)2(aq) + 2NO(g) + 4H2O(l) What are some indications that a chemical reaction has taken place? • A gas is given off • A color change occurs • 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(s) + 8HNO3(aq) 3Cu(NO3)2(aq) + 2NO(g) + 4H2O(l) We saw the temperature of the solution increase. Was energy absorbed or released by this reaction? 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(s) + 8HNO3(aq) 3Cu(NO3)2(aq) + 2NO(g) + 4H2O(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. A better way to write is as an ionic equation.

31. 3Cu(s) + 8H+ + 8NO3- 3Cu2+ + 6NO3-+ 2NO(g) + 4H2O(l) 3Cu(s) + 8HNO3(aq) 3Cu(NO3)2(aq) + 2NO(g) + 4H2O(l) Now, everything that exists as an ion, is written as an ion.

32. 3Cu(s) + 8H+ + 8NO3- 3Cu2+ + 6NO3-+ 2NO(g) + 4H2O(l) The reaction is between the atoms of copper and the nitrate ion. This produces copper ions and NO gas. But NO gas is a colorless gas. Where does the brown gas come from?

33. There is a “side-reaction”, in which NO gas reacts with the oxygen gas, O2, in the air to make NO2. 2NO(g) + O2(g) 2NO2(g) And NO2 is a reddish-brown, vile smelling, somewhat toxic gas.

34. 3Cu(s) + 8H+ + 8NO3- 3Cu2+ + 6NO3-+ 2NO(g) + 4H2O(l) 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. Oxidizing and reducing agents The Copper Cycle Lab Activity series REDOX Solubility rules 1. Synthesis 2. Decomposition 3. Single replacement 4. Double replacement 5. Combustion of a hydrocarbon 1. Precipitate 2. Gas given off 3. Temperature change 4. Color change Predicting products Types of reactions Evidence of reaction Balancing Equations Copper Lab Stock system Net ionic equations Nomenclature Acids Stoichiometry Acid/base neutralization Reaction rate factors pH and [H+] 1. Concentration 2. Temperature 3. Surface area 4. Catalyst Strong & weak Thermodynamics Endothermic & exothermic Activation energy Reaction pathway diagrams

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