Chapter 12 - Acids and Bases

I. Properties of Acids and Bases

• ACIDS

1. Taste sour
2. Reach with certain metals (Zn, Fe, etc.) to produce hydrogen gas
3. cause certain organic dyes to change color
4. react with limestone (CaCO3) to produce carbon dioxide
5. React with bases to form salts and water

• BASES

1. Taste bitter
2. feel slippery or soapy
3. react with oils and grease
4. cause certain organic dyes to change color
5. react with acids to form salts and water

• Define:
  • Acid - a substance that produces protons, H⁺
  • Base - a substance that produces hydroxide ions, OH^-

II. Reaction of acids and bases with water:

• Acids and bases form ions in solution:
  HCl(aq) ® H⁺(aq) + Cl^-(aq)
• H₃O⁺ - hydronium ion H⁺ and H₃O⁺ are equivalent in aq. solution
• When we look at the reactions of acids - can be generalized using hydrogen ion

1. Reaction with zinc yields hydrogen gas
2. Reaction with limestone - produce CO2(g)
3. Acids react with bases to produce a salt

• Similarly for bases, produce hydroxide ions

III. Neutralization and Salts

• Neutralization - one type of double replacement reaction
• Acid + Base ® Salt + water
• Net ionic equation shows what drives the neutralization reaction

example:

Molecular: HCl(aq) + NaOH(aq) ® NaCl(aq) + H2O(l)

Total Ionic: H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) ® Na+(aq) + Cl-(aq) + H2O(l)

Net Ionic: H+(aq) + OH-(aq) ® H2O(l)

• SALT - a salt is formed from the anion of the acid and the cation of the base - usually present as spectator ions. - not always NaCl
  

IV. Types of Acids

• Monoprotic - a solution that produces one mole of H+ ions per mole of acid
  HCl , HNO3
• Diprotic - a solution that produces two moles of H+ ions per mole of acid
  H2SO4
• Triprotic - a solution that produces three moles of H+ ions per mole of acid
  H3PO4
• Polyprotic - two ore more H+ per mole of acid

V. Polyprotic acids:

• can be Partially neutralized
• acid salt - an ionic compound containing the anion with one or more hydrogens that can be neutralized with a base

VI. Strengths of Acids and Bases:

• STRONG ACIDS
  • Acids that are essentially 100% ionized in aqueous solutions
  • ex: HCl, HNO3, HClO4
  • produce the maximum concentration of H+
  • [acid] = [H+]
• WEAK ACIDS
  • Acids that are partially ionized ( usually less than 5%) in equilibrium.
  • HF + H2O(l) H3O+(aq) + F-(aq)
  • The forward and the reverse reaction are occurring simultaneously most found as HF.
• STRONG BASES
  • those compounds that completely ionize in water to produce OH- ions
  • NaOH(s) ® Na+(aq) + OH-(aq)
  • Concentration of base = concentration of hydroxide ions
• WEAK BASES
  • NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)
  • equilibrium lies far to the left (mostly reactants present)

VII. Equilibrium of Water

• H2O(l) + H2O(l) H3O+(aq) + OH-(aq)
• Autoionization - produces positive and negative ions from the dissociation of the molecules of a liquid.
• Experimentally, found concentration of ions = 1.0 x 10-7 M at 25° C
• [H3O+][OH-] = Kw
• at 25° C (1.0 x 10-7)(1.0 x 10-7) = 1.0 x 10-14
• Kw = ION PRODUCT - gives us the concentrations of hydronium and hydroxide ions in pure water and acidic and basic solutions

VIII. pH Scale - another way of writing concentrations.

• pH = -log[H3O+] pOH = -log[OH-]
• pH = 1.00 Þ [H3O+] = 1.0 x 10-1M
• pH = 7.00 Þ [H3O+] = 1.0 x 10-7M
• Sig. Figs:

1. The number of sig figs to the right of decimal in pH equals the number of total sig. figs. in the concentration.
2. The total number of sig. figs. in the concentration equals the number of sig. figs. to the right of the decimal in the pH.

IX. Similarly for hydroxide

• pOH = -log[OH-]
• pOH = 1.00 Þ [OH-] = 1.0 x 10-1M
• pOH = 7.00 Þ [OH -] = 1.0 x 10-7M

.

• pH + pOH = 14.000

X. Brønsted-Lowry Acids and Bases

• acid - a proton (H+) donor
• base - a proton (H+) acceptor

NH3(aq) + H2O(aq) ® NH4+(aq) + OH- (aq)

• NH3 and NH4+ are conjugate acid-base pairs
• H2O and OH- are conjugate acid-base pairs

• Amphiprotic - a compound or ion that can either donate or accept H+ ions.
  H2O, HSO4- , HPO42-, HSO3- etc.

XI. Predicating acid base reactions in water:

• Acid-Base reactions always yield conj. acid-base
• Strong Acid ® weak conj. base
• Strong Base ® weak conj. acid
• Weak Acid ® strong conj. base
• Weak Base ® strong conj. acid
• The strength of the reactant compared to the strength in the product determines which direction the equilibrium lies.
• Three predictions can be made:
  • The reactant may Not react at all, leaving essentially all reactants (negligible)
  • The reactants may Slightly react, leaving mostly reactants (limited)
  • The reactants may react (essentially) completely, leaving little or no reactants (favorable)

XI. Acidic and Basic Salt solutions:

• Hydrolysis - the reaction of an anion with water to produce OH- or the reaction of a cation to produce H3O+ .
• Neutral solutions of salts: Cation does not undergo hydrolysis
  Anion does not undergo hydrolysis
• Basic solutions of salts: Cation same as above
  Anion undergoes some hydrolysis
• Acidic solutions of salts: Cation undergoes some hydrolysis
  Anion does not
• Complex solutions: Cation and anion undergoes hydrolysis
  Then you need to know the relative strength of each.

XII. Buffer solutions

• Buffer solution - resists changes in pH caused by the addition of limited amounts of a strong acid or a strong base.
• A buffer solution must contain:
  A weak acid + its conjugate base
  or A weak base + its conjugate acid