1 Acids, Bases and PH

2 Some Properties of Acids þ Produce H + (as H 3 O + ) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) þ Taste sour þ Corrode metals þ Electrolytes þ React with bases to form a salt and water þ pH is less than 7 þ Turns blue litmus paper to red “Blue to Red A-CID”

3 Some Properties of Bases  Produce OH - ions in water  Taste bitter, chalky  Are electrolytes  Feel soapy, slippery  React with acids to form salts and water  pH greater than 7  Turns red litmus paper to blue “Basic Blue”

4 Acid/Base definitions Definition #1: Arrhenius Acids:– produce H + ions (or hydronium ions H 3 O + ) Bases:– produce OH - ions (problem: some bases don’t have hydroxide ions!)

5 Arrhenius acid is a substance that produces H + (H 3 O + ) in water Arrhenius base is a substance that produces OH - in water

6 Definition #2: Brønsted – Lowry Acids:– proton donor Bases:– proton acceptor A “proton” is really just a hydrogen atom that has lost it’s electron!

7 A Brønsted-Lowry acid is a proton donor A Brønsted-Lowry base is a proton acceptor acid conjugate base base conjugate acid

8 The Brønsted definition means NH 3 is a BASE in water — and water is itself an ACID

9 Conjugate Pairs

10 Learning Check! Label the acid, base, conjugate acid, and conjugate base in each reaction: HCl + OH -  Cl - + H 2 O H 2 O + H 2 SO 4  HSO H 3 O +

11 Lewis acid:- a substance that accepts an electron pair. Lewis base:- a substance that donates an electron pair. Definition #3 – Lewis

12 Formation of hydronium ion is also an excellent example. Lewis Acids & Bases Electron pair of the new O-H bond originates on the Lewis base.Electron pair of the new O-H bond originates on the Lewis base.

13 HNO 3, HCl, H 2 SO 4 and HClO 4 are strong acids. Strong and Weak Acids/Bases The strength of an acid (or base) is determined by the amount of IONIZATION.

14 Weak acids are much less than 100% ionized in water.Weak acids are much less than 100% ionized in water. One of the best known is acetic acid = CH 3 COOH Strong and Weak Acids/Bases

15 Strong Base: 100% dissociated in water.Strong Base: 100% dissociated in water. NaOH (aq) ---> Na + (aq) + OH - (aq) NaOH (aq) ---> Na + (aq) + OH - (aq) Strong and Weak Acids/Bases Weak base: less than 100% ionized in waterWeak base: less than 100% ionized in water One of the best known weak bases is ammonia NH 3 (aq) + H 2 O (l)  NH 4 + (aq) + OH - (aq)

16 Equilibria Involving Weak Acids and Bases Consider acetic acid, HC 2 H 3 O 2 (HOAc) HC 2 H 3 O 2 + H 2 O  H 3 O + + C 2 H 3 O 2 - Acid Conj. base (K is designated K a for ACID) K gives the ratio of ions (split up), to molecules (don’t split up).

17 Ionization Constants for Acids/Bases Acids ConjugateBases Increase strength

18 The pH scale is a way of expressing the strength of acids and bases. Under 7 = acid 7 = neutral Over 7 = base The pH scale

19 pH of Common Substances

20 Calculating the pH pH = - log [H+] (Remember that the [ ] mean Molarity) Example: If [H + ] = 1 X pH = - log 1 X pH = - (- 10) pH = 10 Example: If [H + ] = 1.8 X pH = - log 1.8 X pH = - (- 4.74) pH = 4.74

21 More Examples: Find the pH of: 1) A 0.15 M solution of Hydrochloric acid. 2) A 3.00 X M solution of Nitric acid.

22 More About Water H 2 O can function as both an ACID and a BASE. In pure water there can be AUTOIONIZATION Equilibrium constant for water = K w K w = [H 3 O + ] [OH - ] = 1.00 x at 25 o C In a neutral solution [H 3 O + ] = [OH - ] = 1.00 x M

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24 pOH pOH does not really exist, but it is useful for changing bases to pH.pOH does not really exist, but it is useful for changing bases to pH. pOH = - log [OH - ] Since pH and pOH are on opposite ends, pH + pOH = 14

25 pH [H + ] [OH - ] pOH

26 Examples: 1- What is the pH of : M NaOH solution? soln: soln: [OH-] = (or 1.0 X M) pOH = - log pOH = - log pOH = 3 pOH = 3 pH = 14 – 3 = 11 OR: K w = [H 3 O + ] [OH - ] K w = [H 3 O + ] [OH - ] [HO + ] = 1.0 x M [H 3 O + ] = 1.0 x M pH = - log (1.0 x ) = 11.00

27 [OH - ] [H + ] pOH pH 10 -pOH 10 -pH -Log[H + ] Log[OH - ] -Log[OH - ] 14 - pOH 14 - pH 1.0 x [OH - ] [OH - ] 1.0 x [H + ] [H + ]

28 The OH - ion concentration of a blood sample is 2.5 x M. What is the pH of the blood? More Examples:

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