CH204 Expt 9 acid base buffers fall09

CH204 Expt 9 acid base buffers fall09 - This Week...

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1 EXPERIMENT 9: ACID-BASE EQUILIBRIA 1 This Week Weak acid titration. ring4 Determine K a of acetic acid by a couple of different methods. ring4 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 ring4 HCl HI HBr (binary) ring4 HClO 3 HClO 4 H 2 SO 4 HNO 3 (oxoacids or ternary acids) ring4 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
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2 Calculating [H 3 O + ] and pH ring4 If you are given the [H 3 O + ] [H + ] = [H 3 O + ] pH = – log[H 3 O + ] ring4 If you are given the pH [H 3 O + ] = 10 –pH 7 Four-Part Lab (part 1) - Calibration ring4 Calibrate pH meter ring4 Make sure you’re in CALIBRATION mode. ring4 Calibrate the pH meter in the order in the lab circle5 manual: pH 7.00 first, then pH 4.01, then pH 10.01 ring4 Press ENTER or CON to confirm calibration. 8 Part 2 – Titration of Weak Acid with Strong Base ring4 Work with a partner. ring4 Titrate 25 ml of 0.1 M acetic acid using 0.1 M NaOH ring4 DO NOT add water! circle5 No indicator this time. circle5 Titrate in a beaker, not a flask, because you need room for the pH electrode.
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