Acids-Bases Arrhenius: Acid…. A substance that increases the hydrogen ion, H +, concentration when dissolved in H 2 O. Eg. HCl, H 2 SO 4, HC 2 H 3 O 2 (CH 3 COOH), etc. Base…. A substance that increases hydroxide ion, OH -, concentration. Eg. NaOH, NH 4 OH, etc. Bronsted-Lowry (1923) (not worried about increasing/decreasing H + or OH - concentrations) Acid … a “proton donor”, p + = H +, any formula HA. Eg. HCl, H 2 SO 4, HC 2 H 3 O 2 (CH 3 COOH), etc. Base …. A “proton acceptor” Eg. OH -, NH 3 ; Cl - Note: HOH can do both! Really no different from Arrhenius. This is different from Arrhenius!

Acid solutions: HCl (g) + H 2 O (l) H 3 O + (aq) + Cl - (aq) H 3 O + (aq) = H + (aq) H:Cl:.. + :O::O: H H H H :O::O: H + + :Cl:.. - Hydrogen ion, H +, or hydronium ion, H 3 O + has formed HCl (g) + H 2 O (l) H + (aq) + Cl - (aq) Bronsted and Lowry would say the HCl donated a p + (H + ion), and the water accepted a p + (H + ion). Either way the HCl is an acid. The water is a base ….it was a proton acceptor! Coordinate covalent bond Arrhenius would say the concentration of H+ has increased.

Strength of an acid can be determined by conductivity. 12 M HCl Good or poor electrolyte? Large or small # of ions? goodLarge HCl (g) + H 2 O (l) H 3 O + (aq) + Cl - (aq) Initially: K a = [H 3 O + ] [Cl - ] [HCl] = Large value Strong Acid Acids with K a values greater then “1” are considered strong acids. They 100% ionize. Note: 100% pure HCl is a poor conductor. Why? No ions!

Strength of an acid can be determined by conductivity. Good or poor electrolyte?Large or small # of ions? Pure HC 2 H 3 O 2 no conduction none Diluted HC 2 H 3 O 2 poor small HC 2 H 3 O 2 (g) + H 2 O (l) H 3 O + (aq) + C 2 H 3 O 2 - (aq) Initially: < 5% ionization….. Very weak acid Weak acid K a = [H 3 O + ][C 2 H 3 O 2 - ] [HC 2 H 3 O 2 ] = a Very small #= 1.76 X 10 -5

Properties of Acids: 1. Conduct electricity if they ionize. 2. React with metals to form H 2 3. Neutralize bases. 4. Turn litmus red 5. Taste sour

More Bronsted-Lowry Acid/Base info: General acid/base reaction: HA + B = A - + HB + acid 1 base 2 base 1 acid 2 conjugate Acid/base pair HCl (aq) + NH 3 (aq) = NH 4 + (aq) + Cl - (aq) acid 1 base 2 acid 2 base 1 Which direction is favored? Which is a stronger acid? HCl…. K a is larger At equilibrium there is more ________________ product

Titration problems What is the volume of a M NaOH solution needed to just neutralize 65.2 ml of 1.37 M HNO 3 ? Balanced equation: 1 NaOH + 1 HNO 3 = 1 HOH + 1NaNO ml xxxxx = = 275ml NaOH Or using: M a V a # H ’ s = M b V b # OH ’ s (1.37M)(65.2ml)(1) = (0.325M)(V b )(1) V b = 275ml * Since they equal the same # of moles!

Basic Solutions: Strong Arrhenius bases: 1.Group IA hydroxides. Eg. NaOH, KOH 2.Lower Group IIA hydroxides. Eg. Sr(OH) 2, Ba(OH) 2 100% “Dissociate”: NaOH (S) Na + (aq) + OH - (aq) 1.0 M Ba(OH) 2 = 1.0mol Ba mol OH - The K b for these bases would be very large; > than 1. They would also be good conductors of electricity. 1.Acid anions of weak acids: eg. C 2 H 3 O 2 -, from HC 2 H 3 O 2 or OH -, from HOH Strong Bronsted-Lowry bases:

More Bronsted-Lowry Acid/Base info : Bases react with water to produce OH - General equation: B (g) + H 2 O (l) = BH + (aq) + OH - (aq) NH 3(g) + H 2 O (l)  NH 4 + (aq) + OH - ( aq ) Base 1 acid 2 acid 1 base 2 K b =[NH 4 + ][OH - ] [NH 3 ] = 1.79 x Which direction is favored in the reaction?

Lewis Acid/Base Lewis acid: electron pair acceptor Lewis base: electron pair donor H+H+ + :N:.. H H H Lewis acid Lewis base.. H H H H ::N + “adduct” … the product of a L.acid/base rxn

Acid-Base Equilibria Review: In pure water & all aqueous solutions: H 2 O + H 2 O = H 3 O + + OH - K w = [ H 3 O + ][OH - ] = 1 x [H 3 O + ] = [OH - ] = 1x or = [H 3 O + ] > [OH - ] = Acidic solution [H 3 O + ] < [OH - ] = Basic solution [H 3 O + ] = [OH - ] = Neutral solution

Solutions of Strong Acids/ Bases: 0.10 M HNO 3 actually consists of 0.10 M H 3 O + or [H + ] = 0.10 M 0.10 M NaOH…. Adds 0.10 OH - to the water solution Ionization & dissociation are 100% for strong acids & bases HNO 3 + H 2 O =  H 3 O + + NO 3 - NaOH + H 2 O =  Na + (aq) + OH - (aq) In 0.10M Ba(OH - ) 2 [OH - ] = GONE In 0.20 M H 2 SO 4 [H + ] = 0.20M 0.40 M

pH A simple scale for ranking the H 3 O + concentrations of dilute acid/base solutions. (Sorenson). pH = - Log [ H 3 O + ] The logarithm of a number is that number expressed as an exponent of the base 10. For example, the logarithm of 1 is 0, 1 x If [H 3 O + ] = = pH = -log = If this is 1 This is the pH 1x

pH Scale neutral pH7 [H3O+][H3O+] 1x10 -7 [OH - ]1x10 -7 pOH 7 Acidity increases [H 3 O + ][OH - ]= 1x pH = - log[H 3 O] pH + pOH = 14 Formulas to remember 1M HA Basicity increases M BOH 10 0

[H 3 O + ] = 3.25 x Given a 3.25 x M HNO 3, solve for: a.[H 3 O + ] a.pH = a.[OH - ] = HNO 3 is a strong acid. Thus, 3.25 x M HNO 3 = -log [3.25 x ] prediction = -(-3.488) = x x = 3.08 x d. pOH =-log [OH - ]= -log [3.08 x ]= 10.5 Or pOH = –3.49 = More About the pH Scale