Chemistry Lect 6

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Indicators usually change color...

within +/- 1 pH point of their pKa
Bronstead Lowry Acid and Base
- Acid: donates a proton
- Base: accepts a proton
Lewis Acid and Base
- Acid: accepts a pair of electrons
- Base: donates a pair of electrons
Arrhenius Acid and Base
- Acid: produces a hydrogen ion (H⁺) in aqueous solu'n
- Base: produces a hydroxide ion (OH^-) in aqueous solu'n
pH
- pH = -log [ H⁺]
- i.e. 4*10^-3--> pH is lower than 3 but higher than 2
- pH = -log (4*10^-3) = 2.4
Acid Strength Related to Conj. Base
- The stronger the acid, the weaker the conj. base
- ** a weak acid however may have a weak or strong conj. base **
Strong Acids
- Hydroiodic - HI
- Hydrobromic - HBr
- Hydrochloric - HCl
- Nitric - HNO₃
- Perchloric - HClO₄
- Chloric - HClO₃
- Sulfuric - H₂SO₄
Strong Bases
- Sodium Hydroxide - NaOH
- Potassium Hydroxide - KOH
- Amide Ion - NH₂^-
- Hydride Ion - H^-
- Calcium Hydroxide - Ca(OH)₂
- Sodium Oxide - Na₂O
- Calcium Oxide - CaO
Acids dissociate ___ in higher concentrated solution.

Less
Acid Strength is Dependent On:
- Bond Strength: the higher the bond strength, the harder it is to remove the proton and the weaker the acid is
- Bond Polarity: the more polar, the easier it is to remove the proton, the more acidic the acid is
- Stability of Conj. Base: the more stable the more acidic
Common Acids Compare Strength
- HF < HCl < HBr < HI
- least --------------> most
Hydrides
- Metal Hydrides = basic or neutral
- Non-Metal Hydrides = acidic or neutral
- acidity tends to increase as we move down the periodic table
Equilibrium Constants For Acid-Base Rxns
- K_w = [H⁺][OH^-] = 10^-14
- pH + pOH = pK_w = 14
- K_a = [H⁺][A^-] / [HA]
- K_b = [OH^-][HA] / [A^-]
- K_b * K_a = K_w
Equivalence Pt
- equal equivalents of acid/base and its conjugate
- 100% A^- (conj)
Half Equivalence Point
- exactly half of the acid/base has been neutralized
- solu'n is considered buffered
- pH = pK_a
- 50% HA and 50% A^-
Henderson Hasselbalch
- pH = pK_a + log [A^-]/[HA]
- remember log (1) = 0 --> this is why the 1/2 equiv. pt is pH = pKa
Indicators
- The range of the indicator is pH = pK_a +/- 1
- endpoint - when the indicator changes color
- usually you choose and indicator whose range will cover the equivalence point
Polyprotic Titrations

Assume the first proton completely dissociates before the second starts
To make a buffered solution we:
- start with an acid whose pKa is closes to the pH at which we want the buffer to be
- mix equal amounts of the acid and its conjugate base

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laskiru

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Chemistry Lect 6

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Acid Base Chemistry

Updated

2011-01-11T20:03:57Z

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