1. Acid-Base Equilibria Chapter 16

2. Acids 1.Have a sour taste. e.g., Vinegar, lemons, limes, sour milk 2.Cause litmus to change from blue to red. 4. Acid solutions conduct electricity. 3. Acids neutralize bases.

3. 1. Have a bitter taste. e.g., caffeine, walnuts, soap 3. Feel slippery. Many soaps contain bases. Bases 5. Basic solutions conduct electricity. 2. Cause litmus to change from red to blue. 4. Bases neutralize acids.

4. Arrhenius acid - a substance that produces H + (H 3 O + ) in water Arrhenius base - a substance that produces OH - in water Theory is restricted to aqueous solutions

5. Brønsted acid - a proton donor Brønsted base - a proton acceptor acid base acid conjugate base base conjugate acid base Conjugate pairs differ by a proton

6. Water acts as a Brønsted-Lowry base and abstracts a proton (H + ) from the acid. As a result, the conjugate base of the acid and a hydronium ion are formed. Fig 16.2 HCl + H 2 O → Cl − + H 3 O +

7. O H H+ O H H O H HH O H - + [] + Acid-Base Properties of Water H 2 O (l) H + (aq) + OH - (aq) H 2 O + H 2 O H 3 O + + OH - acid conjugate base base conjugate acid autoionization of water

8. H 2 O (l) H + (aq) + OH - (aq) The Ion Product of Water K c = [H + ][OH - ] [H 2 O] [H 2 O] = constant K c [H 2 O] = K w = [H + ][OH - ] Ion-product constant (K w ) - the product of the molar concentrations of H + and OH - ions at a particular temperature. At 25°C: K w = [H + ][OH - ] = 1.0 x 10 - 14 [H + ] = [OH - ] [H + ] > [OH - ] [H + ] < [OH - ] Solution is: neutral acidic basic

9. What is the concentration of OH - ions in a HCl solution whose hydrogen ion concentration is 1.3 M? K w = [H + ][OH - ] = 1.0 x 10 - 14 [H + ] = 1.3 M [OH - ] = KwKw [H + ] 1 x 10 -14 1.3 = = 7.7 x 10 -15 M

10. pH – A Measure of Acidity pH = −log [H + ] [H + ] = [OH - ] [H + ] > [OH - ] [H + ] < [OH - ] Solution is: neutral acidic basic [H + ] = 1 x 10 -7 [H + ] > 1 x 10 -7 [H + ] < 1 x 10 -7 pH = 7 pH < 7 pH > 7 At 25°C pH[H + ] pH = − log [H 3 O + ]

11. pOH = -log [OH - ] [H + ][OH - ] = K w = 1.0 x 10 -14 -log [H + ] – log [OH - ] = 14.00 pH + pOH = 14.00 Fig 16.5 H + concentrations and pH of common substances

12. The pH of rainwater collected in a certain region of the northeastern United States on a particular day was 4.82. What is the H + ion concentration of the rainwater? pH = - log [H + ] [H + ] = 10 -pH = 10 -4.82 = 1.5 x 10 -5 M The OH - ion concentration of a blood sample is 2.5 x 10 -7 M. What is the pH of the blood? pH + pOH = 14.00 pOH = -log [OH - ]= -log (2.5 x 10 -7 )= 6.60 pH = 14.00 – pOH = 14.00 – 6.60 = 7.40

13. Acids and Bases Other “p” Functions The “p” in pH tells us to take the negative base - 10 logarithm of the quantity (in this case, hydronium ions) Some similar examples:  pOH = -log [OH − ]  pK w = -log K w  pCl = -log [Cl − ]

14. Acids and Bases  For less accurate measurements:  Litmus paper “Red” paper turns blue above ~pH = 8 “Blue” paper turns red below ~pH = 5  Indicator:

15. Acids and Bases  For more accurate measurements:  pH meter, which measures the voltage in the solution Fig 16.6 Digital pH meter