1 The Chemistry of Acids and Bases

2 Acid and Bases

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5 Some Properties of Acids þ Produce H + (as H 3 O + ) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) þ Taste sour þ Corrode metals þ Electrolytes þ React with bases to form a salt and water þ pH is less than 7 þ Turns blue litmus paper to red “Blue to Red A-CID”

6 Some Properties of Bases  Produce OH - ions in water  Taste bitter, chalky  Are electrolytes  Feel soapy, slippery  React with acids to form salts and water  pH greater than 7  Turns red litmus paper to blue “Basic Blue”

7 Some Common Bases NaOH KOH Ba(OH) 2 Mg(OH) 2 Al(OH) 3 sodium hydroxidelye potassium hydroxideliquid soap barium hydroxidestabilizer for plastics magnesium hydroxide“MOM” Milk of magnesia aluminum hydroxideMaalox (antacid) Formula Name Common Name

8 Acid Nomenclature Binary  Ternary An easy way to remember which goes with which… “In the cafeteria, you ATE something ICky”

9 Acid Nomenclature Flowchart

10 HBr (aq)HBr (aq) H 2 CO 3H 2 CO 3 H 2 SO 3H 2 SO 3  hydrobromic acid  carbonic acid  sulfurous acid Acid Nomenclature Review

11 Try these HI (aq)HI (aq) HCl (aq)HCl (aq) H 2 SO 4H 2 SO 4 HNO 3HNO 3 H 2 CO 3H 2 CO 3 Hydroiodic Acid Hydrochloric Acid Sulfuric Acid Nitric Acid Carbonic Acid

12 Try these HBr (aq)HBr (aq) HBrO 3 (aq)HBrO 3 (aq) H 2 SO 3H 2 SO 3 HClO 4HClO 4 HC 2 H 3 O 2HC 2 H 3 O 2 Hydrobromic Acid Bromic Acid Sulfurous Acid Perchloric Acid Acetic Acid

13 Acid/Base definitions Definition #1: Arrhenius (traditional) Acids – produce H + ions (or hydronium ions H 3 O + ) Bases – produce OH - ions (problem: some bases don’t have hydroxide ions!)

14 Definition #2: Brønsted–Lowry Acids – proton donor Bases – proton acceptor A “proton” is really just a hydrogen atom that has lost it’s electron! Acid & Base Definitions PDA (proton donated acid) BAD (Brønsted–Lowry acid donates)

15 Acid A Brønsted-Lowry Acid is a proton donor Base A Brønsted-Lowry Base is a proton acceptor AcidBase Conjugate Acid The Brønsted definition means NH 3 is a Base in water — and water is itself an Acid Conjugate Base ACID-BASE THEORIES

16 Conjugate Pairs Conjugate Acid – the remaining ion or molecule that can re-accept the proton and act as a base Conjugate Base – the species that is formed when a Brønsted-Lowry base gains a proton.

17 Acids & Base Definitions Lewis acid - a substance that accepts an electron pair Lewis base - a substance that donates an electron pair Definition #3 – Lewis

18 Formation of hydronium ion is an excellent example. Lewis Acids & Bases Electron pair of the new O-H bond originates on the Lewis base.Electron pair of the new O-H bond originates on the Lewis base.

19 Acids & Base Definitions Summary

20 SOME DEFINITIONS Amphoteric - A substance that can act as either an acid or a base, e.g., H 2 O, HCO 3 -Amphoteric - A substance that can act as either an acid or a base, e.g., H 2 O, HCO 3 - Polyprotic acid or base - An acid or base that can donate or accept more than one proton or hydroxide, e.g., H 3 PO 4, H 2 CO 3, H 4 EDTA…Ba(OH) 2, Al(OH) 3Polyprotic acid or base - An acid or base that can donate or accept more than one proton or hydroxide, e.g., H 3 PO 4, H 2 CO 3, H 4 EDTA…Ba(OH) 2, Al(OH) 3

21 The strength of an acid (or base) is determined by the amount of IONIZATION. Strong and Weak Acids/Bases Generally divide acids and bases into STRONG or WEAKGenerally divide acids and bases into STRONG or WEAK

22 HNO 3 (aq) + H 2 O (l) --> H 3 O + (aq) + NO 3 - (aq) HNO 3 is about 100% dissociated in water. Strong and Weak Acids/Bases HNO 3, HCl, HBr, HI, H 2 SO 4 and HClO 4 are among the only known strong acids. STRONG ACID:

23 The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H + (or OH - ) ion. Under 7 = acid 7 = neutral Over 7 = base

24 pH of Common Substances

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27 Calculating the pH pH = - log [H+] (Remember that the [ ] mean Molarity) Example: If [H + ] = 1.0 X pH = - log 1.0 X pH = - (- 10) pH = Example: If [H + ] = 1.8 X pH = - log 1.8 X pH = - (- 4.74) pH = 4.74

28 1) Solution A [H 3 O + ] = 5.89 x pH = ? 2) Solution B [H 3 O + ] = x pH = ? 3) Solution C [H 3 O + ] = 1.05 x pH = ? 4) Solution D [H 3 O + ] = 1.00 x pH = ? Determine the pH of the following H 3 O + concentrations

29 1) Solution A [H 3 O + ] = 5.89 x pH = ) Solution B [H 3 O + ] = x pH = ) Solution C [H 3 O + ] = 1.05 x pH = ) Solution D [H 3 O + ] = 1.0 x pH = 6.00 Determine the pH of the following H 3 O + concentrations

30 pH calculations – Solving for H+ If the pH of Coke is 3.120, [H 3 O + ] = ??? Because pH = - log [H 3 O + ] then - pH = log [H 3 O + ] - pH = log [H 3 O + ] Take antilog (10 x ) of both sides and get 10 -pH = [H 3 O + ] [H 3 O + ] = = 7.59 x M *** to find antilog on your calculator, look for “Shift” or “2 nd function” and then the log button *** to find antilog on your calculator, look for “Shift” or “2 nd function” and then the log button

31 pOH Since acids and bases are opposites, pH and pOH are opposites! pOH is useful for changing bases to pH. pOH looks at the perspective of a base pOH = - log [OH - ] Since pH and pOH are on opposite ends, pH + pOH = 14

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33 The pH of rainwater collected in a certain region of the northeastern United States on a particular day was What is the H + ion concentration of the rainwater?

34 pH[H 3 O + ]pOH[OH - ] x x x x x x x 10 -5

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39 pH testing There are several ways to test pH –Blue litmus paper (red = acid) –Red litmus paper (blue = basic) –pH paper (multi-colored) –pH meter (7 is neutral, 7 base) –Universal indicator (multi-colored) –Indicators like phenolphthalein –Natural indicators like red cabbage, radishes

40 pH indicators Indicators are dyes that can be added that will change color in the presence of an acid or base. Some indicators only work in a specific range of pH Once the drops are added, the sample is ruined Some dyes are natural, like radish skin or red cabbage

41 The pigment in red cabbage juice is anthocyanin, which changes color from red in acid solution to purplish to green in mildly alkaline solution to yellow in very alkaline solution.

42 Other pH Indicators

43 Universal Indicator 1.Determine the pH to the tenth and ion concentration of the following unknown solution given the color of each indicator:  Phenolphthalein - colorless  Universal indicator – red-orange  Bromcresol Green – yellowish green 1.Determine the pH to the tenth and ion concentration of the following unknown solution given the color of each indicator:  Phenolphthalein - colorless  Universal indicator – red-orange  Bromcresol Green – yellowish green

44 Universal Indicator 2.Determine the pH to the tenth and ion concentration of the following unknown solution given the color of each indicator:  Alzarin Yellow R – yellow  Phenolphthalein - pink  Thymolphthalein –blue 2.Determine the pH to the tenth and ion concentration of the following unknown solution given the color of each indicator:  Alzarin Yellow R – yellow  Phenolphthalein - pink  Thymolphthalein –blue

45 Universal Indicator 3.Determine the pH to the tenth and ion concentration of the following unknown solution given the color of each indicator:  Methyl Orange – yellowish orange  Chlorphenol Red – yellow  Bromthymol Blue – yellow  Bromcresol Green – blue 3.Determine the pH to the tenth and ion concentration of the following unknown solution given the color of each indicator:  Methyl Orange – yellowish orange  Chlorphenol Red – yellow  Bromthymol Blue – yellow  Bromcresol Green – blue

46 ACID-BASE REACTIONS Titrations H 2 C 2 O 4 (aq) + 2 NaOH(aq) ---> acid base acid base Na 2 C 2 O 4 (aq) + 2 H 2 O(liq) Carry out this reaction using a TITRATION. Oxalic acid, H 2 C 2 O 4

47 Setup for titrating an acid with a base

48 TitrationTitration 1. Add solution from the buret. 2. Reagent (base) reacts with compound (acid) in solution in the flask. 3.Indicator shows when exact stoichiometric reaction has occurred. (Acid = Base) This is called NEUTRALIZATION. This is called NEUTRALIZATION.