The Nature of Acid-Base Equilibria

Properties of Acids and Bases Sour taste (vinegar) Bitter taste (baking soda) React with some metal to form H2 gas (Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g) Feels slippery (soap) Turns blue litmus red Turns red litmus blue Colourless in phenolphthalein Pink in phenolphthalein Conduct electricity

Acids and Bases Arrhenius Acids and Bases Acid: produce H+ (or H3O+) when dissolved in water  H3O+ = hydronium ion, H+ + H2O  H3O+  HCl(aq) + H2O  H3O+(aq) + Cl-(aq)  Base: produce OH- when dissolved in water  NaOH + H2O  Na+(aq) + OH-(aq) Bronsted-Lowry Acids and Bases Acid: proton donor HF + H2O  H3O+ + F- (HF acts as acid, H2O acts as base) Base: proton acceptor  NH3 + H2O  NH4+ + OH- (NH3 acts as base, H2O acts as acid) NB: H2O is amphoteric (can act as an acid and a base)

Conjugate Acid-Base Pairs the formula of conjugate acids and bases differ by only one proton Water Conjugate Base (acetate ion) of Acetic Acid Conjugate Acid of Water Water

Conjugate Acid-Base Pairs CH3COOH + H2O  CH3COO- + H3O+ acetic acid = acid (proton donor) water = base (proton acceptor) acetate ion = conjugate base of acetic acid hydronium ion = conjugate acid of water NH3 + H2O  NH4+ + OH- ammonia = base (proton acceptor) water = acid (proton donor) ammonium = conjugate acid of ammonia hydroxide = conjugate base of water

Identifying Acid-Base Conjugate Pairs Ex: HCN + H2O  H3O+ + CN- HCN is the acid, CN- is its conjugate base H2O is the base, H3O+ is its conjugate acid CH3COO- + H2O  CH3COOH + OH– H2O is the acid, OH - is its conjugate base CH3COO- is the base, CH3COOH is its conjugate acid

Strengths of Acids and Bases Strong Acids and Bases: complete ionization HCl(aq) + H2O  H3O+(aq) + Cl-(aq) NaOH + H2O  Na+(aq) + OH-(aq) Strong acids and bases are good electrolytes Weak Acids and Bases: incomplete ionization HC2H3O2 + H2O ↔ C2H3O2- + H3O+ NH3 + H2O ↔ NH4+(aq) + OH-(aq) Weak acids and bases are poor electrolytes A weak acid exists in equilibrium with its conjugate base. A weak base exists in equilibrium with its conjugate acid. Strength ≠ Concentration Strength describes the degree of ionization while Concentration describes the number of moles in a volume of solution i.e. 1.0 M HCl and 1.0 M H2CO3 (same concentrations but HCl is stronger acid)

Types of Acids Monoprotic Acids Diprotic Acids Triprotic Acids can only donate one acidic proton eg: HCl + H2O  H3O+ + Cl-  Diprotic Acids can donate two acidic protons eg: H2SO4 + H2O  H3O+ + HSO4- HSO4- + H2O  H3O+ + SO42-  Triprotic Acids can donate three acidic protons eg: H3PO4 + H2O  H3O+ + H2PO4- H2PO4- + H2O  H3O+ + HPO42- HPO42- + H2O  H3O+ + PO43-

pH Scale pH is a measure of the acidity of a substance acidity is directly related to the [H3O+] therefore pH is directly related to [H3O+] pH is a logarithmic scale Therefore battery acid is not just twice as acidic as lemon juice…it is 10x more acidic (101)….and battery acid is 100x (102) more acidic than vinegar

Why is Pure Water Neutral? Self-ionization of water H2O + H2O  H3O+(aq) + OH-(aq) this reaction does not occur to any great extent. [H3O+] = 1.00 x 10-7 mol/L [OH-] = 1.00 x 10-7 mol/L Because [H3O+] = [OH-] are equal, water is neutral. Also, since pH = -log [H3O+] pH = -log [1.00 x 10-7] pH = 7 Also note pOH = 7.00

Ion Product Constant of Water, Kw H2O  H+(aq) + OH-(aq) Kw = [H+][OH-] The Ion Product Constant of Water Kw = [1 x 10-7][1 x 10-7] Kw = 1.0 x 10-14 (@25°C – its temp dependent) Also, -logKw , or pKw = 14.00 Since Kw is the product of [H+] x [OH-], then… pH + pOH = 14.00

Good Things to Know [H3O+] = [OH-] neutral [H3O+] > [OH-] acidic [H3O+] < [OH-] basic

Calculating pH i.e. Determine the pH of a 0.1M solution of HCl.    i.e. What is the pH of a 0.0027M solution of H2SO4? i.e. What is the pH of a 1M NaOH solution?

Calculating pH  i.e. The pH reading of a solution is 10.33. What is the hydrogen ion concentration?      i.e. What is the hydrogen ion concentration for a solution with a pH of 4.62?

Calculating pH  i.e. Find [H3O+] and [OH-] in a 2.5 mol/L nitric acid solution.      i.e. Find [H3O+] and [OH-] in a 0.16 mol/L barium hydroxide solution.

Calculating pH  i.e. Determine the [H+] of a 500.0 mL solution that contains 2.6 g of NaOH Water taken from a lake was found to have [H+]=3.2x10-5 M. Calculate the pH and pOH.     

Measuring pH acid-base indicator a chemical substance that changes colour when the pH of the system changes. Ex: litmus pH meter electronic instrument that measure the voltage between electrodes in a solution and displays the measurement as a pH.

HOMEWORK pg. 532 # 1-2 pg. 537 # 4-6 pg. 540 # 8-11 pg. 546 # 12-14