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lecture 3

# lecture 3 - Todays Lecture Announcements Act 1 Artwork of...

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Today’s Lecture Announcements Act 1: Artwork of Acids Act 2: Hi, my name is Hydronium and I have a proton condition

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Announcements Engineering Seminars Thursday’s 11:30 – 12:30 ETB1, check it! Reading (covered today) Benjamin, Chapter 3 and 4 Problem sets PS 1 & 2 to be graded and solution posted on Monday PS 3 out tomorrow (will be due in two weeks but problems will be added after next weeks lecture) Project – will be posted tomorrow
Quiz Draw a log C-pH diagram for a 10 -2 M acetic acid solution (pK a = 4.76). -14 -12 -10 -8 -6 -4 -2 0 0 2 4 6 8 10 12 14 pH log C [H+] [OH-] [HA or BH+] [A- or B]

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Quiz Draw a log C-pH diagram for a 10 -2 M acetic acid solution (pK a = 4.76). -14 -12 -10 -8 -6 -4 -2 0 0 2 4 6 8 10 12 14 pH log C [H+] [OH-] [HA or BH+] [A- or B]
Act 1: Artwork of Acids Graphical Solutions: Acids and Bases

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Graphical Solutions What is the pH of vinegar? 5 v/v% acetic acid, CH 3 COOH (HAc), pK a = 4.76 convert v/v concentration to molar 50 mL HAc/1000 mL solution HAc density = 1.05 g mL -1 HAc molecular weight = 60 g mol -1 TOTAc = 0.88 M = 10 -0.06 M log TOTAc = -0.06
Graphical Solutions How to do these problems: 1. Identify the ingredients in the “recipe” 2. Identify species expected at equilibrium 3. List equilibrium constants for the reactions 4. List mole balances 5. Write charge balance 6. (Determine activity coefficients)

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Graphical Solutions Identify ingredients in the recipe what went into the solution? H 2 O, 55.6 M acetic acid (HAc), 10 -0.06 M
Graphical Solutions Identify species present at equilibrium all must come from reactions involving the ingredients H 2 O = H + + OH - species: H 2 O, H + , OH - (these are always present) {H 2 O} not unknown; {H 2 O} = 1 always H + and OH - called “ type a species HAc = H + + Ac - species: HAc, (H + ), Ac - (already have H + ) acid and conjugate bases called “ type b ” species

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Graphical Solutions Identify species present at equilibrium all must come from reactions involving the ingredients salts that are very soluble (e.g., NaCl, CaSO 4 ) assume that they completely dissolve e.g., NaCl Na + + Cl - no K values needed called “ type c ” species complexes; combinations of b and c called “ type d ” species X
Graphical Solutions List equilibrium constants for reactions H + ,OH - ( type a ) HAc, Ac - (acids, bases; type b ) completely soluble salts; type c complexes of b and c ; type d one K value for each species    w K H OH       a H Ac K HAc

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Graphical Solutions List mole balance equations these equations represent conservation of mass list by ion ion or molecule “in its most dissociated form” H 2 O, H + , OH - excluded here n eqns = n type b + n type c for the aqueous phase mass can be lost to gas or solid phases consider all b (acid and base), c (salts), and d (complexes) species
Graphical Solutions For the acetic acid solution: number of mass balance equations needed n eqns = n type b + n type c = 1 + 0 n eqns = 1 TOTAc name equation after de-protonated form     0.06 10 M TOTAc HAc Ac 

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Graphical Solutions Write charge balance electroneutrality where c i
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lecture 3 - Todays Lecture Announcements Act 1 Artwork of...

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