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! 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™? SWBAT . . . . . . list the observable properties of acids, bases, and salt solutions. And NO CONTACT LENSES on lab days! Okay, well, maybe I am irritating, but I’m not corrosive. No, wait, I’m not the corrosive & irritating one. Just remember to wear your goggles during labs, okay? ACIDS and BASES are corrosive and irritating. 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 . . . 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. “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” http://www.burnsurgery.org/Betaweb/Modules/initial/part_two/sec6.htm Alkali burn sodium hydroxide burn http://www.enotes.com/topic/Chemical_burn Acid “cooks” flesh. BASE ACID Bases taste bitter. Acids taste sour. Acids, bases, and salts are all electrolytes, although some are strong and some are weak. -+ + + - +- + + - - + pure water electrolyte = ? (has freely wandering ions) (a non-electrolyte) 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 Acids are more famous for being metaldestroyers, 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. 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. METAL HYDROXIDES tend to be BASES. Alakali metals react with water to form metal hydroxides. 2Li + 2H2O H2 + 2LiOH Q: What is the formula of the hydroxide ion? 2Na + 2H2O H2 + 2NaOH A: OH- 2K + 2H2O H2 + 2KOH Q: Why do alkali metals form hydroxides? A: Alkali metals have one 2Rb + 2H2O H2 + 2RbOH valence electron, so they like to lose it to empty their outer shell, rendering 2Cs + 2H2O H2 + 2CsOH them positive, which attracts them to negative 2Fr + 2H2O H2 + 2FrOH (?) ions like hydroxide. alkali burn fun at the beach! HCl + NaOH NaCl + H2O Acid burn ACID + BASE SALT + WATER (usually) 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. SWBAT . . . . . . Define acids and bases in terms of ion donation and acceptance. OH + H Acid: a substance that gives off H+ ions in water. HCl H+ + Cl- H+ = “hydrogen ion” Svante Arrhenius 1859-1927 Base: a substance that gives off OH- ions in water. NaOH Na+ + OHOH- = “hydroxide ion” 1 H Hydrogen 1.01 All that’s left is just a single, lonely . . . + When it had an electron, it was a hydrogen atom . . . proton. + H Now that it’s lost its electron, it has become a hydrogen ion. 1 H Hydrogen 1.01 + + = proton H + H H 2O OH Acid: a substance Base: a substance that gives off H+ ions that gives off OH- ions in water. 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 . . . 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! Speaking of ammonia . . . NH3 is a base, but where’s the OH? NH3 + H2O NH4+ + OHJohannes Bronsted Thomas Lowry NH3 doesn’t give OH-, but it does take H+. Acids donate hydrogen ions. Bases accept hydrogen ions. 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). 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 OHions in water. Q: What is the Bronsted-Lowry definition of acids and bases? A: Acids give H+ ions. Bases take H+ ions. SWBAT . . . . . . Explain how the self-ionization of water relates to Kw 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. Our notions of (at least the older definitions of “acid” and “base”) are prejudiced by the fact that Earth is a mostly watercovered planet and, that, consequently, Earth’s creatures, including people, are made mostly of water. Water molecules are very stable. Nonetheless, every once in a while, a water molecule breaks in two. H2O H+ + OH- 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. 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 > 99.9% H+ + OH- << 1% The percentages listed here are quite rough. We can be even more precise if we want to. 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 > 99.9% H+ + OH- << 1% The percentages listed here are quite rough. We can be even more precise if we want to. H+ + OH- In pure water, the concentration of broken water molecules is 10-7M That’s the same thing as 10-7 mol/L 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. H+ + OH- In pure water, only one out of every 556,000,000 water molecules is broken. That’s about 0.002 ppm H2O H2O + H2O H+ + OH- H3O+ + OH- 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 Equilibrium: H+ + OH- 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. LeChatelier’s Principle H2O H+ + OH- 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. LeChatelier’s Principle H2O + OHH+ 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 LeChatelier’s Principle H2O + OHH+ 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 LeChatelier’s Principle H2O + OHH+ 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 LeChatelier’s Principle H2O + OHH+ 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? H+ = 3 6 4 OH- = 3 1 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 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 2 x 12 = 24 If [H+] = 10-12M, then [OH-] = 10-2M If [H+] = 10-1M, then [OH-] = 10-13M 3 x 8 = 24 4 x 6 = 24 6 x 4 = 24 If [H+] = 10-7M, then [OH-] = 10-7M If [H+] = 1M, then [OH-] = 10-14M SWBAT . . . . . . use the pH system to characterize acid, base, and salt solutions. - + 0 7 14 Click the link below to an FDA web page listing pH’s of different foods. http://www.engineeringtoolbox.com/ food-ph-d_403.html According to this web page, what is the overwhelming tendency for the pH of foods? Foods tend to be . . . . . . the esoteric version . . . “pH” stands for “potential hydrogen”. (maybe) pH is a weird, numerical way of showing the hydrogen ion concentration in a solution. Mathematically, pH = -log[H+] That’s slightly confusing even if you know what logs are. log(10n) = n log(1000) = 3 log(10) = 1 log(1,000,000) = 6 log(100) = 2 log(50) = 1.6987. . . log(0.1) = -1 log(1) = 0 log(0.0001) = - 4 log(1013) = 13 log(10-5) = -5 Let’s give an example of pH: normal water. In normal water, the hydrogen ion concentration is 10-7M. In other words, [H+] = 10-7M. Since pH = -log[H+] . . . The pH of normal water would be 7. In sea water, however, the pH is 8. What would the hydrogen ion concentration be in sea water? In sea water, [H+] = 10-8M. That’s a little more basic than pure water. H2SO4 Car batteries are filled with very dangerous sulfuric acid. In battery acid, one of the most corrosive acids there is, the hydrogen ion concentration is about 1M. 1 = 100, so . . . In battery acid, the pH is . . . 0 Lemon juice is one of the most acidic foods you can eat. In lemon juice, the hydrogen ion concentration is about 10-2M. In lemon juice, the pH is . . . 2 That’s not as strong as battery acid, but it can still rot your teeth. Sodium hydroxide is a strong base. It’s also known as “lye” and turns fat into soap, which makes it a handy drain opener. In a concentrated sodium hydroxide solution, the hydrogen ion concentration can be about 10-14M. In such a concentrated solution of sodium hydroxide, the pH is . . . 14 A typical pH for vinegar is 3. What would the hydrogen ion concentration be in vinegar? In vinegar, [H+] = 10-3M. That’s not quite as acidic as lemon juice or battery acid, but that’s still pretty sour. High [H+] Low pH + H Low [H+] High pH High [OH-] Low pOH OH Low [OH-] High pOH 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, just for fun and review, tell me the pH for each of the following solutions, and tell me if it’s acid, base, or neutral. pH = 3 (acid) If [H+] = 10-3M, then [OH-] = 10-11M pH = 12 (base) If [H+] = 10-12M, then [OH-] = 10-2M pH = 1 (acid) If [H+] = 10-1M, then [OH-] = 10-13M pH = 7 (neutral) If [H+] = 10-7M, then [OH-] = 10-7M pH = 0 (acid) If [H+] = 1M, then [OH-] = 10-14M pH + pOH = 14 If the pH of a concentrated sodium hydroxide solution is 14, Then the pOH is . . . zero Low pH = acid (<< 7) High pOH pH of 7 = neutral (like water) Medium pOH High pH = base (>7) Low pOH High [H+] or low [H+]? Example #1 High [OH-] or low [OH-]? High pH or low pH? High pOH or low pOH? H+ H+ Acid, base or neutral? H+ H+ H+ H+ OH- H+ High [H+] or low [H+]? Example #2 High [OH-] or low [OH-]? High pH or low pH? High pOH or low pOH? H+ H+ OHH+ OH- Acid, base or neutral? OHOH- OH- OH- OH- H+ +] or low [H+]? High [Hmedium Example #3 -] or low [OH-]? High [OHmedium medium High pH or low pH?= 7 High pOH or low pOH?= 7 medium H+ OH- OHH+ OH- H+ OH- H+ OHH+ Acid, base or neutral? Q: What is “[H+]”? A: [H+] = hydrogen ion concentration, in mol/L Q: What is the mathematical definition of pH? A: pH is -1 times the log of hydrogen ion concentration. In other words, pH = -log[H+] Q: What kinds of materials have what kinds of pH’s? A: Acids have pH’s less than 7, bases higher than 7, neutral materials (like pure water) equal to 7. Q: What kinds of pH’s do you get when [H+] is low and when [H+] is high? A: Low [H+] high pH. High [H+] low pH. Q: What is the relationship between pH and pOH? A: pH + pOH = 14; low pH means high pOH & vice versa. SWBAT . . . . . . define what “strong” and “weak” mean when used to describe acids and bases. H molecule that Cl HCl H splits Every single water Cl H enters theCl up H ions. Clinto Therefore, HCl is considered to be a “strong” acid. Cl H Cl H Cl H - - + - - + + + - + - + - + H H H H O Only of the CH COOH molecules O splitHinto ions. O O O some 3 O O O O O In fact, most of them did not. C C C C CH3COOH is a “weak acid”. C H C H C H C H H H H C H H H CH H H H H + - STRONG ACIDS: HCl H2SO4 HBr HNO3 HI HClO4 WEAK ACIDS: HF anything with COOH HF + H2O F- + H3O+ all other acids H2SO4 H3PO4 CH3COOH HCl HNO3 CH3(CH2)16COONa NaOH NaHCO3 NH3 KOH NH4OH Ca(OH)2 HOOC–CH2–COH(COOH)–CH2–COOH hydrochloric acid Hacetic H3PO4 2SO4 acid CH3COOH HCl “monoprotic” HNO3 CH3(CH2)16COONa NaOH 5% NaHCO3 NH3 KOH NH4OH Ca(OH)2 HOOC–CH2–COH(COOH)–CH2–COOH 85% H2SO4 H3PO4 CH3COOH HCl HNO3 CH3(CH2)16COONa NaOH NaHCO3 NH3 KOH NH4OH Ca(OH)2 HOOC–CH2–COH(COOH)–CH2–COOH diprotic H2SO4 H3PO4 sulfuric CH3COOH acid “weak” HCl CH3(CH2)hydronium 16COONa ion NaHCO3 NaOH NH3 KOH HNO3 NH4OH Ca(OH)2 HOOC–CH2–COH(COOH)–CH2–COOH H3O+ “STRONG” http://www.youtube.com/watch?v=100Bk580mPY&feature =youtube_gdata_player Don’t be fooled by the H3. H3PO4 may be “triprotic”, H2SO4but H3PO4 none of the H’s come off CH3COOH easily. HCl HNO3 H3PO4 is a strong molecule, so it is a “weak” acid. CH3(CH2)16COONa phosphoric acid NaHCO3 NaOH NH3 KOH NH4OH Ca(OH)2 HOOC–CH2–COH(COOH)–CH2–COOH methyl group carboxylic acid group H H C H C O O H formula? C2H4O2 acetic acid ethanoic acid CH3COOH H2SO4 H3PO4 CH3COOH HCl HNO3 CH3(CH2)16COONa NaOH NaHCO3 NH3 KOH NH4OH Ca(OH)2 HOOC–CH2–COH(COOH)–CH2–COOH nitric acid H2SO4 H3PO4 CH3COOH HCl CH3(CH2)16COONa NaOH NaHCO3 NH3 KOH HNO3 NH4OH Ca(OH)2 HOOC–CH2–COH(COOH)–CH2–COOH 721-815 AD nitric acid Abu Musa Jābir ibn Hayyān O H H C O O O H2SO4 H3PO4 C ? H ? C CH? O 3COOH H HCl O HNO3 H H CH3(CH2)C16COONa C NaOH C H NHH3 O NaHCO3 KOH citric acid Ca(OH) NH4OH 2 HOOC–CH2–COH(COOH)–CH2–COOH Metal hydroxides are sodium hydroxide CH (CH ) COONa generally bases. 3 2 16 H2SO4 H3PO4 Group 1A & 2A metals are NaHCO3 NaOH especially famous for CH3COOH reacting with water to form KOH NH3 alkaline solutions. HCl HNO3 NH4OH Ca(OH)2 HOOC–CH2–COH(COOH)–CH2–COOH sodium stearate H2SO4 H3PO4 CH3COOH HCl HNO3 CH3(CH2)16COONa NaOH NaHCO3 NH3 KOH NH4OH Ca(OH)2 + HOOC–CH2–COH(COOH)–CH2–COOH H2SO4 H3PO4 CH3COOH HCl HNO3 CH3(CH2)16COONa NaHCO NaOH 3 ammonia KOH NH3 Ca(OH)2 HOOC–CH2–COH(COOH)–CH2–COOH NH3 is a base. According to Arrhenius, though, it can’t be a base. Why? It has no OH to give off. But all experimental evidence shows that ammonia is a base. ???!!! NH3 + H2O NH4+ + OHNH3 is a gas when pure, but, it dissolves in water very readily. When it does, some of the ammonia molecules even steal protons from water! Stealing protons is the opposite of giving protons, so ammonia is the opposite of an acid. Ammonia is a base. Ammonia is a weak base. Johannes Bronsted Thomas Lowry Acids donate hydrogen ions. Bases accept hydrogen ions. H2SO4 H3PO4 CH3COOH HCl HNO3 CH3(CH2)16COONa NaHCO NaOH 3 ammonia KOH NH3 Ca(OH)2 HOOC–CH2–COH(COOH)–CH2–COOH ammonium NH4OH hydroxide H2SO4 H3PO4 CH3COOH HCl HNO3 CH3(CH2)16COONa NaOH NaHCO3 NH3 KOH NH4OH Ca(OH)2 HOOC–CH2–COH(COOH)–CH2–COOH Q: What is the difference between a monoprotic acid, a diprotic acid, and a triprotic acid? A: A monoprotic acid has one H+ to give away. A diprotic acid has two H+’s to give away. A triprotic acid has three. Q: When you see “COOH” in a formula, what does this indicate? A: The chemical is a weak acid. Q: What is the difference between a strong acid and a weak acid? A: Strong acids completely dissociate in water. Weak acids do not. (Same thing for strong vs weak bases.) Q: How many strong acids are there? Name them. A: Six: HCl, HBr, HI, H2SO4, HNO3, HClO4. SWBAT . . . . . . Predict and explain the outcome of acid-base neutralization reactions. sodium hydrogen carbonate CH (CH ) COONa 3 2 16 H2SO4 H3PO4 NaHCO3 NaOH CH3COOH KOH NH3 HCl HNO + 3 NH4OH Ca(OH)2 HOOC–CH2–COH(COOH)–CH2–COOH BASE NaHCO3 + ACID CH3COOH WATER SALT NaCH3COO + CO2 + H2O Acids and bases neutralize each other, turning into salt and water in the process. HCl + NaOH NaCl + H2O HCl + KOH KCl + H2O HBr + CsOH CsBr + H2O H2SO4 + Cu(OH)2 CuSO4 + 2H2O CH3COOH + NaOH NaCH3COO + H2O CH3COOH + RbOH RbCH3COO + H2O H2CO3 + 2LiOH LiHCO3 + LiOH + H2O Li2CO3 + 2H2O H2CO3 + Ca(OH)2 CaCO3 + 2H2O H2SO4 + Mg(OH)2 MgSO4 + 2H2O Acids and bases neutralize each other, turning into salt and water. ACID WATER HCl + NaOH NaCl + H BASE SALT 2O ACID HCl + BASE KOH SALT KCl + HWATER 2O SALT + H BASE CsBr WATER HBr + CsOH ACID 2O WATER SALT 4 + 2H BASE 2 CuSO HACID 2SO4 + Cu(OH) 2O SALT BASE NaCH CHACID H2O 3COOH + NaOH 3COO + WATER SALT BASE RbCH CHACID WATER 3COOH + RbOH 3COO + H 2O WATER BASE LiHCO3 + LiOH + H2O LiSALT HACID 2CO3 + 2LiOH 2CO3 + 2H 2O SALT 3 + 2H BASE 2 CaCO WATER HACID 2CO3 + Ca(OH) 2O SALT BASE WATER HACID 2SO4 + Mg(OH)2 MgSO4 + 2H 2O SWBAT . . . . . . recall that proteins are polymers made of amino acid monomers. Protein is a polymer made of amino acid monomers. amino acid amino acid amino acid amino acid amino acid amino acid amino acid amino acid amino acid amino acid amino acid amino acid An amino acid can neutralize itself. H ? “Amino” refers to ammonia. Ammonia = NH3. amino N It’s part acid, part base. The name “amino acid” is kind of misleading. H C H “Amino acid” sort of means “base acid”. C O O + H H amino acid acid Ammonia is a base. We’ll learn more about amino acids in our next unit . . . . . . ORGANIC CHEMISTRY. Until then . . . Okay, now it’s probably time to * Turn in the Chapter 19 Packet. * Take the Ch 19 Quiz Next meeting, there may be a lab. Dress for lab next meeting. (No contact lenses, no sandals, etc..) B’dee-uh b’dee-uh b’dee-uh That’s all folks!