Acid Reactions I Acids & Active Metals: Single replacement reactions Active metals (K, Na, Ca, Mg, Al, Zn, Fe, Sn) Produce H 2 Oxidation-reduction reactions 1 Example: calcium solid + HCl Ca (s) + HCl (aq)  CaCl 2 (aq) + H 2 (g)2 Zn and HCl

Acid Reactions II Acids, Carbonates and Bicarbonates H + from acid transferred to carbonate Carbonate breaks down rapidly Products: CO 2 H 2 O salt (ionic compound) 2 Example: NaHCO 3 (aq) + HCl (aq)  H 2 CO 3 (aq) + NaCl (aq) CO 2 (g) + H 2 O (l)

Acid Reactions III Neutralization Reactants: acid + base Products: water + salt 3 Example: HCl (aq) + NaOH (aq)  HOH (l) + NaCl (aq) H 2 O (l)H + (aq) + OH - (aq)  Molecular equation: Net ionic equation:

Acid-Base Titration Titration: Neutralize an unknown acid sample with a known amount of base Indicator: changes color when pH changes Example: phenolphthalein 4 Colorless (acidic) Pink (basic) Add base Add base

Acid-Base Properties of Salt Solutions Salts dissolve in water Which salts form… Neutral Solutions? Basic Solutions? Acidic Solutions? 5 cation from strong base and anion from strong acid NaNO 3 NaNO 3 (s)Na + (aq) + NO 3 - (aq) 

Basic and Acidic Salt Solutions Basic solutions form from salts that contain: Acidic solutions form from salts that contain: 6 cation from strong base and anion from weak acid NaF NaF (s)Na + (aq) + F - (aq) cation from weak base and anion from strong acid NH 4 Cl NH 4 Cl (s)NH 4 + (aq) + Cl - (aq)

Buffers Buffer solutions resist a change in pH –Ex. Blood (pH ~ 7.4) Acid must neutralize small amounts of base Base must neutralize small amounts of acid Acid and base must not neutralize each other 7 Use conjugate acid-base pairs! CH 3 COOH (aq) + H 2 O (l)CH 3 COO - (aq) + H 3 O + (aq) Added in as salt (NaCH 3 COO)

Buffers weak acid + its salt (containing conjugate base) 8 CH 3 COOH (aq) + H 2 O (l)CH 3 COO - (aq) + H 3 O + (aq) You have prepared a buffer with 0.90 M CH 3 COOH and 1.2 M CH 3 COO-. (K a for acetic acid = 1.8 x ). What is the equilibrium expression for this buffer? What is the [H 3 O + ] in this solution? What is the pH of this solution?

Making a buffer We want to make 100. mL of a pH 4 citric acid/sodium citrate buffer with an acid concentration of 0.5 M. We are given solid sodium citrate (294 g/mol) and 5.0 M citric acid. The pKa of citric acid is Henderson-Hasselbalch equation