1 EXPERIMENT 9: ACID-BASE EQUILIBRIA 1 This Week Weak acid titration. r Determine K a of acetic acid by a couple of different methods. r Witness the power of a buffer solution to resist changes in pH. 2 Non-Equilibrium Reaction 3 Ionization is complete in dilute aqueous solution. 2 2 3 100% 100% H O H O HCl H O Cl in dilute solution NaOH Na OH in dilute solution +-+-→ + ⇒ → + ⇒ Equilibrium Reaction Ionization is incomplete in dilute aqueous solution. 4 2 2 3 3 3 3 4 less than 1% ionization NH less than 1% ionization H O H O CH COOH CH COO H O NH OH-+ +-→ + ⇒ ← → + ⇒ ← Equilibrium Expression 5 K a = [H 3 O + ][A – ] [HA] For any equilibrium reaction, aA + bB ⇄ cC + dD For a weak acid dissociation, HA ⇄ H 3 O + + A – K eq = [ C] c [D] d [A] a [B] b products reactants Seven Strong Acids r HCl HI HBr (binary) r HClO 3 HClO 4 H 2 SO 4 HNO 3 (oxoacids or ternary acids) r Weak Acids 6 All the rest! CH 3 COOH, R-COOH, HNO 2 H 3 PO 4 , HF, NH 4 + , HCN, HBrO 3 “HA” abbreviation
2 Calculating [H 3 O + ] and pH r If you are given the [H 3 O + ] [H + ] = [H 3 O + ] pH = – log[H 3 O + ] r If you are given the pH [H 3 O + ] = 10 –pH 7 Four-Part Lab (part 1) - Calibration r Calibrate pH meter r Make sure you’re in CALIBRATION mode. r Calibrate the pH meter in the order in the lab c manual: pH 7.00 first, then pH 4.01, then pH 10.01 r Press ENTER or CON to confirm calibration. 8 Part 2 – Titration of Weak Acid with Strong Base r Work with a partner. r Titrate 25 ml of 0.1 M acetic acid using 0.1 M NaOH r DO NOT add water! c No indicator this time. c Titrate in a beaker, not a flask, because you need room for the pH electrode. 9
This is the end of the preview. Sign up to
access the rest of the document.