Acids and Bases. Two important classification of compounds - Acids and Bases. Properties of BASES

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1 ACIDS AND BASES

2 Acids and Bases Two important classification of compounds - Acids and Bases Properties of ACIDS Taste Sour/Tart Stings and burns the skin Reacts with bases Turns blue litmus paper red Reacts with metals to form H 2 gas Neutralizes Bases Donates H + Conduct electricity. Can be strong or weak electrolytes in aqueous solution Properties of BASES Taste Bitter Feels slippery on skin Reacts with acids Turns red litmus blue Doesn t react with metals Neutralizes Acids Accepts H +

3 Acids Affect Indicators Blue litmus paper turns red in contact with an acid.

4 Acids React with Active Metals Acids react with active metals to form salts and hydrogen gas: HCl (aq) + Mg (s) MgCl 2(aq) + H 2(g)

5 Sulfuric Acid H 2 SO 4 Highest volume production of any chemical in the U.S. Used in the production of paper Used in production of fertilizers Used in petroleum refining

6 Nitric Acid HNO 3 Used in the production of fertilizers Used in the production of explosives Nitric acid is a volatile acid its reactive components evaporate easily Stains proteins (including skin!)

7 Hydrochloric Acid - HCl Used in the pickling of steel Used to purify magnesium from sea water Part of gastric juice, it aids in the digestion of proteins Sold commercially as Muriatic acid

8 Phosphoric Acid H 3 PO 4 o A flavoring agent in sodas o Used in the manufacture of detergents o Used in the manufacture of fertilizers o Not a common laboratory reagent

9 Acetic Acid HC 2 H 3 O 2 Used in the manufacture of plastics Used in making pharmaceuticals Acetic acid is the acid present in household vinegar

10 Bases Affect Indicators Red litmus paper turns blue in contact with a base. Phenolphthalein turns purple in a base.

11 Examples of Bases Sodium hydroxide (lye), NaOH Potassium hydroxide, KOH Magnesium hydroxide, Mg(OH) 2 Calcium hydroxide (lime), Ca(OH) 2

12 Bases Neutralize Acids Milk of Magnesia contains magnesium hydroxide, Mg(OH) 2, which neutralizes stomach acid, HCl. 2 HCl + Mg(OH) 2 MgCl H 2 O

13 Acid-Base Theories Arrhenius (1883) HCl NaOH H 2 SO 4 2- CO 3 NH 3 H 2 O BF Brønsted Lowry (1923) 3 AlI 3 Lewis ( )

14 Arrhenius Definition of A & B An acid is a substance that dissociates in water to produce hydrogen ions (H + ) Example: Hydrochloric Acid (HCl) A base is a substance that dissociates in water to produce hydroxide ions (OH - ) Example: Sodium Hydroxide (NaOH)

15 What happens when placed in water???

16 Svante Arrhenius ( )

17 Brønsted-Lowry Definition An acid is any substance that can donate H + ions. A base is any substance that can accept H + ions. Expansion on Arrhenius definition of A&B Defines A&B as not necessarily in water solution Does not contain OH - ; covers bases such as ammonia NH 3

18 Johannes Bronsted Thomas Lowry ( ) ( )

19 Brønsted-Lowry Definition H + is really only just a proton (no electrons or neutrons), so definition is often in terms of protons Brønsted-Lowry Base is a proton acceptor Brønsted-Lowry Acid is a proton donor Monoprotic Acids can only donate 1 H + : HCl Diprotic Acids can donate 2 H + : H 2 SO 4 Triprotic Acids can donate 3 H + : H 3 PO 4 Polyprotic acids = diprotic and triprotic acids

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22 Conjugate Acid-Base Pairs Acid-base reactions with water proceed in both directions: Example: NH 3 (g) + H 2 O (l) Acid loses H + = conjugate base NH 4+ (aq) + OH - (aq) Example: H 2 O (acid) loses its H +, turning it into OH - (conjugate base) Base gains H + = conjugate acid Example: NH 3 (base) gains an H +, turning it into NH 4 + (conjugate acid)

23 Acids and bases come in pairs A conjugate base is the remainder of the original acid, after it donates it s hydrogen ion A conjugate acid is the particle formed when the original base gains a hydrogen ion Indicators are weak acids or bases that have a different color from their original acid and base

24 The Hydronium Ion Water can pick up a H + ion to form a hydronium ion: H + + H 2 O H 3 O + H 3 O + = hydronium ion With acids, water is a Brønsted-Lowry base (accepts protons Example: HCl (g) + H 2 O(l) H 3 O + (aq) + Cl - (aq) With bases, water is a Brønsted-Lowry acid (donates protons) Example: NH 3 (g) + H 2 O (l) NH 4+ (aq) + OH - (aq) Compound that can act as either a proton donor or acceptor = amphoteric

25 Lewis Acids and Bases Gilbert Lewis ( ) Gilbert Lewis focused on the donation or acceptance of a pair of electrons during a reaction Lewis Acid - electron pair acceptor Lewis Base - electron pair donor Most general of all 3 definitions; acids don t even need hydrogen!

26 Lewis Acids and Bases Lewis acid = accepts a pair of electrons during a reaction Lewis base = donates a pair of electrons during a reaction Covers acids and bases not covered by Brønsted- Lowry definition Type Acid Base Table 19.4, Pg. 592, Text Arrhenius H + producer OH - producer Brønsted-Lowry H + (proton) donor H + acceptor Lewis Electron-pair acceptor Electron-pair donor

27 The ph Scale ph is based on the concentration of the hydronium ion in a solution Concentrations range from 10 0 M (strong) to M (weak) of [H 3 O + ] ph ranges from 0 to 14 If [H ] concentration = 10-2 M, ph = 2 If [H ] concentration = M, ph = 10 Water is 10-7 M, ph = 7 ph of 0-6 = Acidic ph of 7 = Neutral ph of 8-14 = Basic

28 ph..defined as the negative base-10 logarithm of the hydronium ion concentration. ph = log [H 3 O + ] For pure H 2 O: [ ] = 7.0 Problem: Calculate ph when [H 3 O + ] = 2.3 x 10-3 M 10 x base 10 log log log * 10^- 3 Problem: Calculate [H 3 O + ] when ph = 2.3? = 2.64 antilog 10 x log 10^ -2.3 = 5.0 * 10-3

29 ph and poh Calculations [OH - ] = 1 x [H + ] H + OH - [H + ] = 1 x [OH - ] [H + ] = 10 -ph ph = -log[h + ] [OH - ] = 10 -poh poh = -log[oh - ] ph poh = 14 - ph ph = 14 - poh poh

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31 ph + poh = 14 ph These are the ph values for several common substances.

32 ph and poh equilibrium in pure Water In pure water, [H 3 O + ] [OH ] = K w [ ] [ ] = log [H 3 O + ] + log [OH ] = log K w ph + poh = pk w Because in pure water [H 3 O + ] = [OH ], K w = [ ] [ ] = = 14

33 ph and poh equilibrium in Water to which Acids & Bases are Added Add base OH - H 2 O(l) + H 2 O(l) H 3 O + (aq) + OH (aq) H 2 O [H 3 O + ] [OH ] K w = [ ] [ ] = K w = [ ] [ ] = ph + poh = pk w = 14

34 Measuring ph Why measure ph? Solutions we use swimming pools soil conditions for plants medical diagnosis soaps and shampoos, etc. Sometimes we can use indicators, other times we might need a ph meter

35 Acid-Base Strength An acid or a base is considered strong if they completely dissociate into ions (H + and OH - ) in water Strong Acids HCl and H 2 SO 4 Strong Bases Hydroxides, e.g. NaOH Conjugate acid-base pairs have an inverse relationship (works for both acids and bases) The stronger the acid, the weaker the conjugate base The weaker the acid, the stronger the conjugate base

36 Strong Acids and Bases to know

37 Measuring ph with wide-range paper 1. Moisten indicator strip with a few drops of solution, by using a stirring rod. 2.Compare the color to the chart on the vial read the ph value.

38 Acid-Base Indicators Although useful, there are limitations to indicators: usually given for a certain temperature (25 o C), thus may change at different temperatures what if the solution already has color, like paint? the ability of the human eye to distinguish colors is limited

39 Some of the many ph Indicators and their ranges

40 Red Cabbage Juice as an indicator Red cabbage juice mixed with baking soda (left) and with vinegar (right). On the top, a drop of unmixed juice.

41 Acid-Base Indicators A ph meter may give more definitive results some are large, others portable works by measuring the voltage between two electrodes; typically accurate to within 0.01 ph unit of the true ph needs to be calibrated

42 Acids Neutralize Bases HCl + NaOH NaCl + H 2 O -Neutralization reactions ALWAYS produce a salt and water. -Of course, it takes the right proportion of acid and base to produce a neutral salt

43 Acid-Base Properties of Salts Neutralization reaction = reaction of an acid and a base Acid + base react form a salt and water Type of salt depends on reactants Acid Base Salt Strong Strong Neutral Strong Weak Acidic Weak Strong Basic Weak Weak Neutral, basic, or acidic

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55 Buffers Buffers are solutions in which the ph remains relatively constant, even when small amounts of acid or base are added made from a pair of chemicals: a weak acid and one of it s salts; or a weak base and one of it s salts

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57 Acid rain

58 Causes of emissions

59 ph readings nationwide

60 Acid rain effects limestone and Marble

61 Effects of Acid Rain on Marble (calcium carbonate) George Washington: BEFORE George Washington: AFTER

62 Naming Acids and Bases Naming Acids: Three Rules 1. Name of anion ends in ide Acid name begins with hydro- Stem of anion has suffix ic 2. Name of anion ends in ite Stem of anion has suffix ous 3. Name of anion ends in ate Stem of anion has suffix ic All three end with the word acid Naming Bases Named just like ionic compounds cation + anion

63 Acid Base Humor