Acids and Bases

1. Acids and Bases Acids Bases Init <<5/12/2008 by Daniel R. Barnes WARNING: This presentation includes a combination of original graphical images created by the author and images taken without specific permission from the world wide web. Do not distribute or copy this presentation. CAUTION: This author uses Wikipedia as though it could be trusted. Uh-BUGGA-BUGGA-BUGGA-BUGGA-BOO!

2. I looked, but I saw nothing in the NGSS that specifically stated that high school students needed to learn general princples about acids and bases. Gulp™?

3. SWBAT . . . . . . list the observable properties of acids, bases, and salt solutions.

4. And NO CONTACT LENSES on lab days! Acids and Bases Acids Bases Just remember to wear your goggles during labs, okay? Okay, well, maybe I am irritating, but I’m not corrosive. irritating corrosive ACIDS and BASES are corrosive and irritating. No, wait, I’m not the corrosive & irritating one.

5. How long are you supposed to wash your eyes out if you get acids or bases or anything else in them? According to the Flinn Scientific Student Safety Contract that you should have signed by now . . . 20 minutes!

6. Too bad we don’t have a second pair of hands on our faces like this. If we did, we could use our regular hands to keep the eyewash handle turned on. Since we don’t have face hands, you’ll need a buddy to keep the eyewash fountains turned on while you hold your eyes wide open with your fingers. Not a problem in room C215!

7. "acid burn" “When acid comes into contact with the body it feels like water. It wets the body and a burning sensation begins that gradually increases in intensity. The patients cry in agony until the chemical is washed away or is neutralized. The affected skin becomes black and leather-like. The chemical also leaves its mark on the healthy skin it trickles over”

8. Bases hurt, too. http://www.burnsurgery.org/Betaweb/Modules/initial/part_two/sec6.htm Alkali burn sodium hydroxide burn http://www.enotes.com/topic/Chemical_burn

9. CEVICHE Acid “cooks” flesh.

10. BASE ACID

11. Bases taste bitter. Acids taste sour.

12. Acids, bases, and salts are all electrolytes, although some are strong and some are weak. + - - + + - - + + + - - - + pure water (a non-electrolyte) electrolyte = ? (has freely wandering ions)

13. Acids react with metals, corroding the metals to form salt and hydrogen gas. Acid + metal  Salt + hydrogen gas Acids are typically stored in glass or plastic containers. You’ll probably never see an acid stored in a metal container. Bases can corrode metal too: http://www.hbscc.nl/publications/23%20alkaline/alkaline2.htm

14. Acids are more famous for being metal-destroyers, but bases are known for attacking metal in some cases, also. http://www.youtube.com/watch?v=WnPrtYUKke8&feature=youtube_gdata_player Thank you, Roberto Pinzon, for giving me this link.

15. HS-PS-2. Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.

16. METAL HYDROXIDES tend to be BASES. Alakali metals react with water to form metal hydroxides. Q: What is the formula of the hydroxide ion? 2Li + 2H2O  H2 + 2LiOH 2Na + 2H2O  H2 + 2NaOH A: OH- Q: Why do alkali metals form hydroxides? 2K + 2H2O  H2 + 2KOH A: Alkali metals have one valence electron, so they like to lose it to empty their outer shell, rendering them positive, which attracts them to negative ions like hydroxide. 2Rb + 2H2O  H2 + 2RbOH 2Cs + 2H2O  H2 + 2CsOH 2Fr + 2H2O  H2 + 2FrOH (?)

17. alkali burn fun at the beach! HCl + NaOH  NaCl + H2O Acid burn + + ACID BASE SALT WATER  (usually)

18. Did you get it? Q: How do acids and bases taste? A: Acids taste sour. Bases taste bitter. Q: Acids and bases may be opposites, but what do they have in common? A: They are both corrosive and irritating. They are both electrolytes. Q: Why is red the symbolic color for acids and blue the symbolic color for bases in this presentation? A: Acids turn litmus paper red and bases turn it blue. Q: What is produced when an acid reacts with a base? A: Salt and water. Q: What is produced when an acid reacts with a metal? A: Salt and hydrogen gas.

19. SWBAT . . . . . . Define acids and bases in terms of ion donation and acceptance.

20. Acids and Bases Acids Bases OH- H+ Acid: a substance that gives off H+ ions in water. Base: a substance that gives off OH- ions in water. Svante Arrhenius 1859-1927 HCl  H+ + Cl- NaOH  Na+ + OH- H+ = “hydrogen ion” OH- = “hydroxide ion”

21. 1 H Hydrogen 1.01 All that’s left is just a single, lonely . . . + . . . proton. Now that it’s lost its electron, it has become a hydrogen ion. When it had an electron, it was a hydrogen atom + H

22. 1 H Hydrogen 1.01 + + H = proton

23. Acids and Bases Acids Bases OH- H+ H2O Acid: a substance that gives off H+ ions in water. Base: a substance that gives off OH- ions in water. Looking at these definitions of “acid” and “base”, one gets the idea that water is “normal”, “neutral”, and “average”, that it is the “middle chemical”. However, I have a nagging feeling that aliens from other planets may not share our view . . .

24. My drink’s getting a little low. You got anything to top it off with? No. God no! Are you trying to poison me? Now you’re talking!

25. Speaking of ammonia . . . NH3 is a base, but where’s the OH? NH3 + H2O  NH4+ + OH- Johannes Bronsted Thomas Lowry NH3 doesn’t give OH-, but it does take H+. Acids donate hydrogen ions. Bases accept hydrogen ions.

26. HONORS BULLETIN Honors students, you are required to learn about Lewis acids and Lewis bases on your own (to the degree that we fail to cover it in class).

27. Did you get it? Q: According to Svante Arrhenius, what is the definition of an acid? A: An acid is a chemical that gives off H+ ions in water. Q: What was his definition of a base? A: Arrhenius said a base was a chemical that gave off OH- ions in water. Q: What is the Bronsted-Lowry definition of acids and bases? A: Acids give H+ ions. Bases take H+ ions.

28. SWBAT . . . . . . Explain how the self-ionization of water relates to Kw

29. HONORS BULLETIN If this is a non-honors chemistry section, or if you’re simply pressed for time, please skip to pH. Honors students are required to learn about Kw on their own even if there’s no time in class.

30. Our notions of Acids and Bases Acids Bases (at least the older definitions of “acid” and “base”) are prejudiced by the fact that Earth is a mostly water-covered planet and, that, consequently, Earth’s creatures, including people, are made mostly of water.

31. Water molecules are very stable. Nonetheless, every once in a while, a water molecule breaks in two. H2O OH- + H+ The hydrogen and hydroxide ions that water breaks into like each other a lot because of their opposite charges, so they get back together again pretty fast. Therefore, the equation for the dissociation of water deserves a double arrow, since it is a reversible reaction.

32. Because water molecules rarely break, and because they get back together again so quickly when they do break, the amount of broken molecules in a quantity of pure water is very low. H2O OH- + H+ << 1% > 99.9% The percentages listed here are quite rough. We can be even more precise if we want to.

33. Because water molecules rarely break, and because they get back together again so quickly when they do dissociate, the amount of broken molecules in a quantity of pure water is very low. H2O OH- + H+ << 1% > 99.9% unbroken broken The percentages listed here are quite rough. We can be even more precise if we want to.

34. In pure water, the concentration of broken water molecules is 10-7M OH- H+ + That’s the same thing as 10-7 mol/L broken water 10-7 mol/L = 0.0000001 mol/L One liter (L) of water has a mass of 1000 g. The molar mass of water is 18 g/mol. (1000 g)/(18 g/mol) = 55.6 mol, so the concentration of water in water is 55.6 mol/L. (55.6 mol/L)/(10-7 mol/L) = 556,000,000 In pure water, only one out of every 556,000,000 water molecules is broken.

35. H+ OH- + BROKEN WATER In pure water, only one out of every 556,000,000 water molecules is broken. That’s about 0.002 ppm

36. The Self-Ionization of Water

37. H+ OH- H2O + H3O+ H2O + H2O OH- +

38. Unless disturbed, aqueous (watery) systems, such as a cup of water, an ocean, a car battery, or your bloodstream, will tend reach a state of equilibrium, in which the forward and reverse reactions shown below occur at equal rates. H2O OH- + H+ Equilibrium: when opposite processes occur at equal rates. Amounts of different chemicals are probably not equal to each other. However, at equilibrium, the amount of each chemical does not change as time goes by. At equilibrium, water molecules fall apart but they come back together again just as quickly as they fall apart.

39. LeChatelier’s Principle H2O OH- + H+ If a system is at equilibrium, the amount of each chemical will remain constant as time goes by. However, if a system at equilibrium is disturbed by some kind of stress, the reaction rates will change in whatever way will oppose the effects of the disturbance. If a bunch of molecules are at equilibrium and you disturb them, the molecules will try to undo the work you have done.

40. LeChatelier’s Principle H2O OH- + H+ Imagine a bathtub full of water. If not disturbed, it will reach an equilibrium with regard to the above reversible reaction. H+ = 3 OH- = 3

41. LeChatelier’s Principle Cl Cl Cl H2O OH- + H+ However, if you raise the [H+], say, by pouring in some hydrochloric acid, this will disturb the equilibrium. Didn’t you see us being in equilibrium? RUDE! Sa-kurity! Oh no you di-ent just add more H+! H+ = 3 6 OH- = 3

42. LeChatelier’s Principle Cl Cl Cl H2O OH- + H+ The system will now do whatever it takes to lower the [H+], to undo what you just did . . . at least partially . . . H+ = 3 6 OH- = 3

43. LeChatelier’s Principle Cl Cl Cl H2O OH- + H+ The equilibrium, as they say, will “shift to the left”. Why? The forward reaction creates H+, but the reverse reaction (going to the left) uses up H+, turning it into water. Did you notice that by adding H+, you made OH- decrease? 1 H+ = 3 6 4 OH- = 3

44. It is generally true that if you make [H+] increase, you will cause a decrease in [OH-]. This is expressed mathematically by the following equation: [H+][OH-] = 10-14M2 If two numbers always multiply to give the same result, then when one of the two numbers gets bigger, the other must get smaller. Take the following example: 1 x 24 = 24 2 x 12 = 24 3 x 8 = 24 4 x 6 = 24 6 x 4 = 24

45. It is generally true that if you make [H+] increase, you will cause a decrease in [OH-]. This is expressed mathematically by the following equation: [H+][OH-] = 10-14M2 Now try some acid-base examples. These examples could be any aqueous (watery) system. If [H+] = 10-3M, then [OH-] = 10-11M 1 x 24 = 24 If [H+] = 10-12M, then [OH-] = 10-2M 2 x 12 = 24 If [H+] = 10-1M, then [OH-] = 10-13M 3 x 8 = 24 If [H+] = 10-7M, then [OH-] = 10-7M 4 x 6 = 24 If [H+] = 1M, then [OH-] = 10-14M 6 x 4 = 24

46. SWBAT . . . . . . use the pH system to characterize acid, base, and salt solutions.

47. - + pH 7 0 14

48. Q: Are students allowed to have acids on campus?

49. pH

50. Click the link below to an FDA web page listing pH’s of different foods. pH http://www.engineeringtoolbox.com/food-ph-d_403.html According to this web page, what is the overwhelming tendency for the pH of foods? Acids Foods tend to be . . .