Friday, March 14, 2008 Turn in Labs Extra Credit Opportunity Review Homework Section 16.1B – Acid Strength Section 16.1C – Water as an Acid and A Base Homework: Page 589, 13, 14, 16, 17, 18, 20, 22bd, 23bd, 24b, 25b

Acid/Base Strength 1.HA(g) + H 2 O(l)  H 3 O + (aq) + A - (aq) When an acid dissolves in water, a proton is transferred from the acid to the water. The new acid (conjugate acid) can react with the conjugate base This reforms the parent acid and water molecule

Acid/Base Strength 1.HA(g) + H 2 O(l)  H 3 O + (aq) + A - (aq) 2.H 3 O + (aq) + A - (aq)  HA(g) + H 2 O(l) The reaction can occur in both directions. A forward direction (1) or the reverse direction (2). The question is, which one wins? Which has more attraction for the H + ? Or which gives up H + better?

Acid/Base Strength 1.HA(g) + H 2 O(l)  H 3 O + (aq) + A - (aq) 2.H 3 O + (aq) + A - (aq)  HA(g) + H 2 O(l) Strong Acid – the acid is completely ionized or completely dissociates ( all the H + is given away). Weak Acid – does not dissociate to a large extent

Acid/Base Strength How can we tell if it is a strong acid? Check to see conductivity! Strong acid will have lots of ions, (H + and Cl - ) and conduct well – weak will not conduct as well

Acid/Base Strength Make a larger arrow to show strength A strong acid: the forward direction dominates A strong acid contains a relatively weak conjugate base A weak acid contains a relatively strong conjugate base

Acid/Base Strength Diprotic acid – can furnish 2 hydrogen Triprotic acid – H 3 PO 4 H 2 SO 4  H + + HSO 4 - HSO 4 - H + + SO 4 2- Oxyacids – Acids containing oxygen Organic acids – have a carbon atom backbone and a carboxyl group C O OHOH

Representation of the behavior of acids of different strengths in aqueous solution.

Relationship of acid strength and conjugate base strength for the dissociation reaction.

Water as an Acid and a Base pH Scale 16.1C-16.2

Ionization and Concentration Amphoteric substance: can behave as an acid or as a base Water is most common Ionization of water transfers a proton from one water molecule to another Forms a hydroxide ion and a hydronium ion

Self-ionization of Water H2O(l) + H2O(l) H3O+(aq) + OH-(aq) One water molecule acts as an acid (donates) and the other as a base (accepts) Forward reaction does not occur much Only a tiny amount of the ions are in pure water

Self-ionization of Water At 25oC actual concentrations are [H3O+] = [OH-] = 1.0 x 10-7 M Concentrations are equal The product of the two concentrations is [H3O+][OH-] = 1.0 x 25oC

Self-ionization of Water Dilute solutions of water, multiply the concentration of these two ions, always get the same number even if the solution isn’t neutral. What is the number? Kw = [H3O+][OH-] = 1.0 x 25oC Kw = [H+][OH-] = 1.0 x 25oC

Self-ionization of Water What will happen if the concentration of H+ increases? If it decreases? If [H+] increases, [OH-] decreases Kw – Ion Product Constant [H3O+] = [OH-] = 1.0 x 10-7 M This is a neutral solution

Classification of Solutions [H+] = [OH-] neutral [H+] > [OH-] acidic [H+] < [OH-] basic Remember: [H+][OH-] = 1 x 10-14

Calculate [H + ] or [OH - ] as required for each of the following solutions at 25 °C, and state whether the solution is neutral, acidic, or basic. a)1.0 x M OH - b)1.0 x M OH - c)10.0 M H x M, basic 1.0 x M, neutral 1.0 x M, acidic Try Practice Problem 16.3 on p.571 –5.0 x M, basic