Intro to Acids & Bases

Properties of Acids & Bases Acids Acids Taste sour Taste sour Reacts with metals Reacts with metals Turns litmus red Turns litmus red Conducts electricity Conducts electricity Base Base Taste bitter Taste bitter Slippery Slippery Turns litmus blue Turns litmus blue Conducts electricity Conducts electricity

Ions in Solution Acidic solutions – contain more H + than OH - Acidic solutions – contain more H + than OH - Basic solutions – contain more OH - than H + Basic solutions – contain more OH - than H + Neutral solutions – contain equal amounts of H + and OH - Neutral solutions – contain equal amounts of H + and OH -

Autoionization of Water H 2 O + H 2 O  H 3 O + + OH - H 2 O + H 2 O  H 3 O + + OH - Water is the usual solvent for acids and bases Water is the usual solvent for acids and bases It produces equal numbers of H 3 O + and OH - It produces equal numbers of H 3 O + and OH -

Arrhenius Model of Acids & Bases Acid: a substance that contains H and ionized to produce H + when dissolved in water. Acid: a substance that contains H and ionized to produce H + when dissolved in water. Base: a substance that contains OH and ionizes to produce OH - when dissolved in water Base: a substance that contains OH and ionizes to produce OH - when dissolved in water

Arrhenius Model of Acids & Bases HCl  H + + Cl - HCl  H + + Cl - HCl contains H and ionizes to form H + HCl contains H and ionizes to form H + This could be an Arrhenius acid This could be an Arrhenius acid NaOH  Na + + OH - NaOH  Na + + OH - NaOH contains OH and ionized to form OH - NaOH contains OH and ionized to form OH - This could be considered an Arrhenius base This could be considered an Arrhenius base

Arrhenius Model of Acids & Bases Although the Arrhenius model is useful in describing many acids and bases, it does not describe them all Although the Arrhenius model is useful in describing many acids and bases, it does not describe them all For example NH 3 contains no OH - ions, but it is a base For example NH 3 contains no OH - ions, but it is a base A model to describe all bases is needed A model to describe all bases is needed

Bronsted-Lowry Model Acid: proton donor Acid: proton donor Base: proton acceptor Base: proton acceptor HX + H 2 0  H 3 O + + X - HX + H 2 0  H 3 O + + X - HX donates an H + to the water molecule HX donates an H + to the water molecule The water takes the H and is there for considered the base The water takes the H and is there for considered the base

Bronsted-Lowry Model Conjugate acid – the species produced when a base accepts the H + ion from the acid Conjugate acid – the species produced when a base accepts the H + ion from the acid Conjugate base – the species produced when the acid gives up its H + Conjugate base – the species produced when the acid gives up its H +

Conjugate Acids & Conjugate Bases Identify the acid, base, conjugate acid, and conjugate base of the following reaction… Identify the acid, base, conjugate acid, and conjugate base of the following reaction… HX + H 2 0  H 3 O + + X - HX + H 2 0  H 3 O + + X - A B CA CB A B CA CB Every Bronsted-Lowry interaction involves conjugate acid base pairs Every Bronsted-Lowry interaction involves conjugate acid base pairs

Conjugate Acids & Conjugate Bases Identify the acid, base, conjugate acid, and conjugate base of the following reaction… Identify the acid, base, conjugate acid, and conjugate base of the following reaction… NH 3 + H 2 0  NH OH - NH 3 + H 2 0  NH OH - B A CA CB B A CA CB

Conjugate Acids & Conjugate Bases What did you notice that was different about the previous two reactions? What did you notice that was different about the previous two reactions? Water was an acid in one and a base in the other Water was an acid in one and a base in the other Amphoteric – substance that can act as either an acid or a base Amphoteric – substance that can act as either an acid or a base

Conjugate Acids & Conjugate Bases Identify the acid, base, conjugate acid, and conjugate base of the following reactions… Identify the acid, base, conjugate acid, and conjugate base of the following reactions… NH OH -  NH 3 + H 2 0 NH OH -  NH 3 + H 2 0 A B CB CA A B CB CA HBr + H 2 O  H 3 O + + Br - HBr + H 2 O  H 3 O + + Br - A B CA CB A B CA CB

Neutralization Reactions Neutralization reactions – acid + base  a salt + water Neutralization reactions – acid + base  a salt + water Neutralization reactions are just a special type of double replacement reactions Neutralization reactions are just a special type of double replacement reactions

Write the equations for the following neutralization reactions Write the equations for the following neutralization reactions Acetic acid and ammonium hydroxide Acetic acid and ammonium hydroxide HCH 3 COO + NH 4 OH  HOH + NH 4 CH 3 COO HCH 3 COO + NH 4 OH  HOH + NH 4 CH 3 COO Nitric acid and cesium hydroxide Nitric acid and cesium hydroxide HNO 3 + CsOH  HOH + CsNO 3 HNO 3 + CsOH  HOH + CsNO 3 Neutralization Reactions

The pH Scale [H + ] is often expressed in very small numbers. Chemists needed an easier way to express [H + ] ions [H + ] is often expressed in very small numbers. Chemists needed an easier way to express [H + ] ions pH is a mathematical scale in which the concentration of hydronium ions in a solution is expressed as a number from 0 to 14. pH is a mathematical scale in which the concentration of hydronium ions in a solution is expressed as a number from 0 to 14. pH = -log[H + ] pH = -log[H + ]

Interpreting the pH Scale pH of 7 is neutral. A pH less than 7 is acidic, and a pH greater than 7 is basic. pH of 7 is neutral. A pH less than 7 is acidic, and a pH greater than 7 is basic.

pH Calculations pH = -log[H + ] pH = -log[H + ] pOH = -log[OH - ] pOH = -log[OH - ] pH + pOH = 14 pH + pOH = 14

Calculating pH What is the pH of a 0.5M HCl solution? What is the pH of a 0.5M HCl solution? 0.5 mol HCl x 1 mol H + = 0.5M H mol HCl x 1 mol H + = 0.5M H + L 1 mol HCl L 1 mol HCl pH = -log[H + ] pH = -log[H + ] pH = -log[0.5] pH = -log[0.5] pH = 0.3 pH = 0.3

Calculating pH Calculate the pH of a M HBr solution. Calculate the pH of a M HBr solution

Calculating pH What if we have a base? What if we have a base? What is the pH of a 0.05M NaOH solution? What is the pH of a 0.05M NaOH solution? 0.05 mol NaOH x 1 mol OH - = 0.05M OH mol NaOH x 1 mol OH - = 0.05M OH - L 1 mol NaOH L 1 mol NaOH pOH = -log[OH - ] pOH = -log[OH - ] pOH = -log[0.05] pOH = -log[0.05] pOH = 1.3 pOH = 1.3 pH + pOH = 14 pH + pOH = 14 pH = 12.7 pH = 12.7

Calculating pH Calculate the pH of a M KOH solution. Calculate the pH of a M KOH solution

Acid/Base Strength The strength of an acid or a base tells you the degree of ionization The strength of an acid or a base tells you the degree of ionization Strong acids & bases break down into many ions Strong acids & bases break down into many ions Weak acids & bases break down into just a few ions Weak acids & bases break down into just a few ions

Acid/Base Strength Strong acidsWeak acids hydrochloric acid, HClacetic acid, CH3COOH hydrobromic acid, HBrhydrocyanic acid, HCN hydriodic acid, HIhydrofluoric acid, HF nitric acid, HNO3nitrous acid, HNO2 sulfuric acid, H2SO4sulfurous acid, H2SO3 perchloric acid, HClO4hypochlorous acid, HOCl periodic acid, HIO4phosphoric acid, H3PO4

Acid/Base Strength Strong basesWeak bases sodium hydroxide, NaOHammonia, NH3 potassium hydroxide, KOHsodium carbonate, Na2CO3 calcium hydroxide, Ca(OH)2potassium carbonate, K2CO3 barium hydroxide, Ba(OH)2aniline, C6H5NH2 sodium phosphate, Na3PO4trimethylamine, (CH3)3N