Acids-Bases Part I 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

Predicting BinaryAcid strength from Periodic Table Position NH 3 H 2 O HF PH 3 H 2 S HCl AsH 3 H 2 Se HBr H 2 Te HI Weaker Stronger Bond energy decreases (size factor) Bond energy decreases EN factor…2 nd element dominates In both cases H separates more easily & acid strength increases

Strength of “Oxyacids” (Oxoacids) The more O’s ….the stronger the acid: KaKa HNO x HNO 3 20 KaKa HClO 3 x HClO x HClO 3 1 x 10 3 HClO 4 1 x 10 7 Monoprotic acids: Diprotic acids: H 2 SO x H 2 SO 4 1 x 10 2 Triprotic acids: H 3 PO x H 2 PO x HPO x

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 = 1mol Ba mol OH - The K b for these bases would be very large; > than 1. They would also be good conductors of electricity. 3.Acid anions of weak acids: eg. C 2 H 3 O 2 -, from HC 2 H 3 O 2 or OH -, from HOH From a Bronsted-Lowry view:

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?

Hydrolysis Salt + H 2 O  Acidic solution Neutral solution Basic solution In water: H 2 O +H 2 O  H 3 O + + OH - K w = 1 x Equal amounts of ions, but very little! Because the [H 3 O + ] = [OH - ]…. Water is neutral If one of the ions from a salt removes one of the ions from the water….the other ion from the water will be in excess! NaCl + HOH : Na + OH - ….100% dissociates! From the NaCl From the H 2 O H + Cl - ….100% ionize From the H 2 O From the NaCl H + not removed Solution is NEUTRAL OH - not removed

NaClO + H 2 O : Predicted base and acid: NaOH vs HClO NaOH…strong base, OH - ion still present in solution HClO…. Weak acid, Solution will be ___________ basic Na + + OH - vs H + + ClO - H + ion removed from solution Hydrolysis (continue)

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