1 The Chemistry of Acids and Bases

2 What is an Acid?

3 Acid and Bases

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6 Acids Have a sour taste. Vinegar is a solution of acetic acid. Citrus fruits contain citric acid. React with certain metals to produce hydrogen gas. React with carbonates and bicarbonates to produce carbon dioxide gas Have a bitter taste. Feel slippery. Many soaps contain bases. Bases

7 -1 Charge- 2 Charge-3 Charge FormulaNameFormulaNameFormulaName H 2 PO 4 - C 2 H 3 O 2 - HSO 3 - HSO 4 - HCO 3 - NO 2 - NO 3 - CN - OH – MnO - ClO - ClO 2 - ClO 3 - ClO 4 - Dihydrogen phosphate Acetate Hydrogen sulfite Hydrogen sulfate Hydrogen carbonate Nitrite Nitrate Cyanide Hydroxide Permanganate Hypochlorite Chlorite Chlorate Perchlorate HPO 4 -2 C 2 O 4 -2 SO 3 -2 SO 4 -2 CO 3 -2 CrO 4 -2 Cr 2 O 3 -2 SiO 3 -2 Hydrogen phosphate Oxalate Sulfite Sulfate Carbonate Chromate Dichromate Silicate PO 3 3- PO 4 3- Phosphite Phosphate 1 + charge FormulaName NH 4 + Ammonium

8 Acids in Chemistry An acid is something that when dissolved in water (broken apart) yields hydrogen cations.

9 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”

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

11 Acid Nomenclature Flowchart

12 Examples HCl (Chloride ends in –ide, therefore changed to –ic and hydro added in front) –Hydrochloric Acid H 2 SO 3 (SO 3 = Sulfite) therefore changed to –ous followed by the word acid –Sulfurous Acid HNO 3 (NO 3 =Nitrate) therefore changed to –ic followed by the word acid –Nitric Acid

13 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

14 Name ‘Em! HI (aq)HI (aq) HCl (aq)HCl (aq) H 2 SO 3H 2 SO 3 HNO 3HNO 3 HIO 4HIO 4

15 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”

16 Some Common Bases NaOHsodium hydroxidelye KOHpotassium hydroxideliquid soap Ba(OH) 2 barium hydroxidestabilizer for plastics Mg(OH) 2 magnesium hydroxide“MOM” Milk of magnesia Al(OH) 3 aluminum hydroxideMaalox (antacid) Al(OH) 3 aluminum hydroxideMaalox (antacid)

17 Strong Acids and Bases Acids are classified as strong or weak by how much they ionize (break apart) in water Strong acids dissociate 100% Strong Bases dissociate 100%

18 Strong Acids Hydrochloric acid: HCl Hydrobromic acid: HBr Hydroiodic acid: HI Sulfuric acid: H 2 SO 4 Nitric acid: HNO 3 Phosphoric Acid: H 3 PO 4

19 Strong Bases Group 1 and Group 2 Hydroxides Lithium hydroxide: LiOH Sodium hydroxide: NaOH Potassium hydroxide: KOH Rubidium hydroxide: RbOH Calcium hydroxide: Ca(OH) 2 Strontium hydroxide: Sr(OH) 2 Barium hydroxide: Ba(OH) 2

20 Acid Base Theories Monoprotic Acids: 1 ionizable hydrogen Diprotic Acids: 2 ionizable hydrogens Triprotic Acids: 3 ionizable hydrogens

21 Ionizable Hydrogens Only hydrogens in very polar bonds, that is those bonding with very electronegative elements are ionizable

22 Examples HCl Ethanoic Acid –CH 3 COOH Methane –CH 4

23 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!)

24 Arrhenius acid is a substance that produces H + (H 3 O + ) in water Arrhenius base is a substance that produces OH - in water

25 Acid/Base Definitions Definition #2: Brønsted – Lowry Acids – proton donor Bases – proton acceptor A “proton” is really just a hydrogen atom that has lost it’s electron!

26 ACID-BASE THEORIES The Brønsted definition means NH 3 is a BASE in water — and water is itself an ACID

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

28 Formation of hydronium ion is also 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.

29 Lewis Acid/Base Reaction

30 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

31 Self-Ionization Process which water molecules produce ions is called self-ionization H 2 O (l) H + + OH - In water or aqueous solution, all H+ ions exist as (H 3 O + )

32 [H + ] and [OH - ] Any solution in which [H + ] and [OH - ] concentrations are equal is called a neutral solution If [H + ] increases, [OH - ] decreases, and the opposite

33 Acidic and Basic Solutions Acidic solutions have more [H + ] than, [OH - ] Basic solutions, also called alkaline solutions, have more [OH - ] than [H + ]

34 pH Because expressing hydrogen ion concentration in molarity is troublesome, the pH system was created pH = - log[H + ] pH expressed between 0 & 14, 0 being the most acidic, 14 the most basic, and 7 being neutral

35 Neutral Solutions In a neutral solution [H + ] = 1 x 10 -7

36 pOH pOH = - log[OH - ] 14- pH= pOH

37 pH of Common Substances

38 pH [H + ] [OH - ] pOH

39 Weak Bases

40 Ionization Constants for Acids/Bases Acids ConjugateBases Increase strength

41 Relation of K a, K b, [H 3 O + ] and pH

42 pH testing There are several ways to test pHThere 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

43 Paper testing Paper tests like litmus paper and pH paperPaper tests like litmus paper and pH paper –Put a stirring rod into the solution and stir. –Take the stirring rod out, and place a drop of the solution from the end of the stirring rod onto a piece of the paper –Read and record the color change. Note what the color indicates. –You should only use a small portion of the paper. You can use one piece of paper for several tests.

44 pH paper

45 pH meter Tests the voltage of the electrolyteTests the voltage of the electrolyte Converts the voltage to pHConverts the voltage to pH Very cheap, accurateVery cheap, accurate Must be calibrated with a buffer solutionMust be calibrated with a buffer solution

46 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