19.2 Reactions of Acids and Bases

1. Dissociation Write the dissociation Rx of Ca(OH) 2 Name: _______________ H 2 SO 3 Name: _______________

2. Neutralization Rx Acids + Bases neutralize each other…. two products 1.Water 2. Salt of the base cation (metal) and the acid anion Example HCl + NaOH→

Practice Neutralization 1.Hydrochloric Acid and Calcium Hydroxide 2. Sulfuric Acid and Aluminum Hydroxide

3. Acids-Metal Rx Acids react with metals to form a)Hydrogen gas b)salt __HCl + __Na →

Practice 1.Sulfuric Acid with Magnesium metal 1.Hydrofluoric Acid and Aluminum

Warm-up: write and complete the following Rx 1.Aluminum hydroxide reacts with sulfurous acid 2. Sulfurous acid in water 3. Hypochlorous Acid reacts with Magnesium metal

Complete the following Rx, name Acid and Bases 1.___Al + ___HClO 3 → 2. ___Al(OH) 3 + ___H 2 SO 4 → aq 2. ___H 2 CO 3 →

Strength of Acids and Bases

Concentration = Strength Concentration of acids and bases is reflected by the [H+] and [OH-] ion concentration. Citric acid: weak acid (you don’t need goggles to peel an orange) but sulfuric acid: strong acid (it makes holes in fabric/paper) The higher the concentration, the stronger the a/b. pH - power of Hydrogen: measures concentration of H+ written as [H+] pOH – opposite to pH is seldom used: pH 0 = pOH 14

Measurement of [H+] square brackets are concentration brackets Problem: mostly very small numbers Ex: H2O: 1 out of 10,000,000 water molecules self- ionize, [H+] = 1/10,000,000

pH value calculations 1/10,000,000 rewrite: 1/1x10 7 rewrite: 1x Take the negative log: -log 1x10 -7 =7.0 pH 7.0 or the pH of water is 7.0 (Little p, big H: round pH to one decimal)

pH of Acids and Bases Acids have more of H+ ions than water Bases have less of H+ ions than water Example: Water HClNaOH Ion.: 1/10,000,000 1/10 1/10 14 [H+]10 -7 M10 -1 M M pH pOH ___ pH+pOH Ex: pH 14 is large number, but it means a low [H+] M pH 1 is a small number, but it means a high [H+] M

H+/OH- concentrations in acids and bases 10 0 H+OH-H+OH-H+OH- H+ OH- H+ OH- H+ OH acid neutral H 2 O base

pH details pH 7 is considered neutral: this [H+] does not harm cells: does not denature proteins or enzymes! pH 0 – 5: will denature proteins: stomach has pH1 to digest proteins! pOH 0- 5 =pH 9-14, will also denature proteins There is a factor of 10x between pH values Ex: pH 5 has ____x ______ [H+] than pH 7

pH of Common Liquids

Practice: calculating pH -log [H+] a) [H+] = 1 x = pH = 4.0 b) [H+] = 3.98 x = pH=10.4 c) [H+] = 1.5 x = pH=1.8 d) [H+] = 6.8 x = pH=7.2

Practice: calculating [H+] pH= →+/-→2 nd log [H+]=2.5 x 10-6 pH = 10.9 [H+]=1.3 x pH = 2.4 [H+]=4.0 x 10-3

Warm-up Write the Rx of 1.Chloric Acid with Iron(II) Hydroxide 2.Ammonia and Hydrochloric Acid 3.Phosphoric Acid and Cadmium Hydroxide

Buffer

Substances that stabilize pH Example: Carbonic Acid and Hydrogen carbonate ion solution H 2 CO 3 /HCO 3 - H 2 CO 3 ↔ H+ + HCO 3 - Add Acid: H+ is neutralized by ____________ Add OH-: OH- is neutralized by _____________

H 2 PO 4 - /HPO 4 2- Write Rx, which acts as acid/base neutralizer?

Expanded acid/base definitions Acids produces H+ ions Bases absorbs H+ ions An acid/base reaction always consists of a conjugate Acid/Base pair Acid Base conjugate conjugate Base Acid HCl + H 2 O ↔ Cl- + H 3 O+

Conjugate Acid/Base Pairs

Warm-up Complete 1.HCl + Mg(OH) 2 → aq 1.H 2 SO 4 → 2.H 3 PO 4 + Mg→

Warm-up Write the Dissociation Rx for 1.Boron Hydroxide 2.Water 3.Ammonia 4.CH 4

Weak and strong Acids/Bases The strength of an A/B does not only depend on the concentration but on the Extend of dissociation Strong acids dissociate 100% Weak acids dissociate less than 100% K acid = [H3O+] x [A-] [HA]

Dissociation constants K of Acids/Bases K acid = [H3O+] x [A-] [HA] 3 Molar solution moles of dissociated acid Ka = M x M = 8.3 x M 0.5 moles dissociate Ka= 0.5 M x 0.5M = 8.3 x M What’s the dissciation constant if all molecules dissociate?

Dissociation of strong and weak acids