1 / 16

Acids - Bases

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.

yoshe
Download Presentation

Acids - Bases

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Acids-Bases Arrhenius: Acid…. A substance that increases the hydrogen ion, H+, concentration when dissolved in H2O. Eg. HCl, H2SO4, HC2H3O2 (CH3COOH), etc. Base…. A substance that increases hydroxide ion, OH-, concentration. Eg. NaOH, NH4OH, etc. Bronsted-Lowry (1923) (not worried about increasing/decreasing H+ or OH- concentrations) Acid … a “proton donor”, p+ = H+, any formula HA. Eg. HCl, H2SO4, HC2H3O2 (CH3COOH), etc. Base …. A “proton acceptor” Eg. OH-,NH3 ; Cl- Note: HOH can do both! Really no different from Arrhenius. This is different from Arrhenius!

  2. Coordinate covalent bond Acid solutions: HCl(g) + H2O(l) H3O+(aq) + Cl-(aq) .. H .. + .. .. H :Cl: H :O: - + .. .. H :O: + :Cl: .. .. H H Hydrogen ion, H+, or hydronium ion, H3O+ has formed H3O+(aq) = H+(aq) HCl(g) + H2O(l)H+(aq)+ Cl-(aq) Arrhenius would say the concentration of H+ has increased. Bronstedand 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!

  3. Strengthof an acid can be determined by conductivity. Good or poor electrolyte? Large or small # of ions? 12 M HCl good Large HCl(g) + H2O(l)H3O+(aq)+ Cl-(aq) Initially: 100 0 0 @equil: 0 100 100 Ka = [H3O+][Cl-] Strong Acid = Large value [HCl] Acids with Ka values greater then “1” are considered strong acids. They 100% ionize. No ions! Note: 100% pure HCl is a poor conductor. Why?

  4. Strengthof an acid can be determined by conductivity. Good or poorelectrolyte? Large or small # of ions? Pure HC2H3O2 no conduction none Weak acid Diluted HC2H3O2 poor small HC2H3O2 (g) + H2O(l)H3O+(aq)+ C2H3O2-(aq) Initially: 100 0 0 @equil: 97 3 3 <5% ionization….. Very weak acid [H3O+][C2H3O2-] Ka = = a Very small # = 1.76 X 10-5 [HC2H3O2]

  5. Properties of Acids: 1. Conduct electricity if they ionize. 2. React with metals to form H2 3. Neutralize bases. 4. Turn litmus red 5. Taste sour

  6. More Bronsted-Lowry Acid/Base info: General acid/base reaction: HA + B = A- + HB+ acid1base2 base1acid2 conjugate pair Acid/base HCl(aq) + NH3(aq) = NH4+(aq) + Cl-(aq) acid1base2 acid2base1 HCl…. Ka is larger Which is a stronger acid? Which direction is favored? product At equilibrium there is more ________________

  7. Titration problems What is the volume of a 0.325 M NaOH solution needed to just neutralize 65.2 ml of 1.37 M HNO3? Balanced equation: 1 NaOH + 1 HNO3 = 1 HOH + 1NaNO3 65.2ml x x x x x = 274.8 = 275ml NaOH * Since they equal the same # of moles! Or using: MaVa#H’s = MbVb#OH’s (1.37M)(65.2ml)(1) = (0.325M)(Vb)(1) Vb = 275ml

  8. Basic Solutions: Strong Arrhenius bases: Group IA hydroxides. Eg. NaOH, KOH 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+2 + 2.0mol OH- The Kb for these bases would be very large; > than 1. They would also be good conductors of electricity. Strong Bronsted-Lowry bases: Acid anions of weak acids: eg. C2H3O2-, from HC2H3O2 or OH-, from HOH

  9. More Bronsted-Lowry Acid/Base info: Bases react with water to produce OH- General equation: B(g) + H2O(l) = BH+(aq) + OH-(aq) NH3(g) + H2O(l) NH4+(aq) + OH-(aq) Base1acid2acid1base2 Kb = [NH4+][OH-] = 1.79 x 10-5 [NH3] Which direction is favored in the reaction?

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

  11. Acid-Base Equilibria Review: In pure water & all aqueous solutions: H2O + H2O = H3O+ + OH- Kw = [H3O+][OH-] = 1 x 10-14 [H3O+] = [OH-] = or = 1x10-7 [H3O+]> [OH-] = Acidic solution [H3O+] <[OH-] = Basic solution [H3O+] = [OH-] = Neutral solution

  12. Solutions of Strong Acids/ Bases: 0.10 M HNO3 actually consists of 0.10 M H3O+ 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 HNO3 + H2O = H3O+ + NO3- NaOH + H2O = Na+ (aq) + OH-(aq) GONE GONE In 0.10M Ba(OH-)2 [OH-] = 0.20M In 0.20 M H2SO4 [H+] = 0.40 M

  13. pH A simple scale for ranking the H3O+ concentrations of dilute acid/base solutions. (Sorenson). pH = - Log [H3O+ ] 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 100. If [H3O+] = 0.001 = pH = -log 0.001 = 1x10-3 This is the pH 3 If this is 1

  14. pH Scale 1M BOH 1M HA Acidity increases Basicity increases neutral pH 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 [H3O+] 100 10-1 10-210-310-410-5 10-6 1x10-7 10-8 10-9 10-10 10-11 10-12 10-13 10-14 [OH-] 10-12 10-8 1x10-7 10-6 10-3 100 8 7 6 3 pOH 12 [H3O+][OH-]= 1x10-14 pH = - log[H3O] pH + pOH = 14 Formulas to remember

  15. More About the pH Scale • Given a 3.25 x 10-4 M HNO3 , solve for: • [H3O+] • pH = • [OH-] = HNO3 is a strong acid. Thus, 3.25 x 10-4M HNO3 = prediction [H3O+] = 3.25 x 10- 4 -log [3.25 x 10-4] = -(-3.488) = 3.49 1 x 10-14 = 3.08 x 10-11 3.25 x 10-4 d. pOH = -log [OH-] = -log [3.08 x 10-11] = 10.5 Or pOH = 14.00 –3.49 = 10.51

More Related