Chemistry B11 Chapter 8 Acids and Bases

DRANO Acids and Bases Acids: sour, squeaky clean Bases: bitter or salty, dirty slimy DRANO

Acids and Bases Acid: produces H3O+ Arrhenius definition: CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq) H3O+ (Hydronium ion): H+(aq) + H2O(l) H3O+(aq) Base: produces OH- H2O NaOH(s) Na+(aq) + OH-(aq) NH3(aq) + H2O(l) NH4+(aq) + OH-(aq) Most Acids release or donate H+ Bases accept H+

Acids and Bases Bronsted and Lowry definition: (If H2O is not involved.) Acid: donates H+ (proton) Base: accepts H+ (proton) CH3COOH + NH3 CH3COO- + NH4+ acid base Conjugate Conjugate acid-base pair

Acids and Bases HCl + H2O Cl- + H3O+ C6H5OH + H2O C6H5O- + H3O+ acid Conjugate base Conjugate acid Conjugate acid-base pair Conjugate acid-base pair C6H5OH + H2O C6H5O- + H3O+ acid base Conjugate base Conjugate acid Conjugate acid-base pair Conjugate acid-base pair

Weak acid or base: is partially ionized in aqueous solution. Acids and Bases Weak acid or base: is partially ionized in aqueous solution. produces less H+ and OH- CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+(aq) NH3(aq) + H2O(l) NH4+(aq) + OH-(aq) Strong acid or base: is completely ionized in aqueous solution. produces more H+ and OH- HCl(aq) + H2O(l) Cl-(aq) + H3O+(aq) NaOH(aq) + H2O(l) Na+(aq) + OH-(aq)

Acids and Bases A strong acid contains a weak conjugate base.

Acids and Bases Monoprotic acids HCl Diprotic acids H2SO4 Triprotic acids H3PO4 Amphiprotic: it can act as either acid or a base. HCl(aq) + H2O(l) Cl-(aq) + H3O+(aq) NaOH(aq) + H2O(l) Na+(aq) + OH-(aq) base acid

Naming binary acids Hydro -ide ion -ic acid Anion : + HF F-: flouride ion Hydroflouric acid HCl Cl-: chloride ion Hydrochloric acid H2S S2-: sulfuride ion Hydrosulfuric acid

Naming ternary acids -ite ion -ous acid Anion: -ate ion -ic acid HNO2 NO2-: Nitrite ion Nitrous acid HNO3 NO3-: Nitrate ion Nitric acid H2CO3 CO32-: carbonate ion carbonic acid H2SO3 SO32-: sulfite ion sulfurous acid

Strong acid pKa < -2 / Weak acid pKa -2 to 12 Ionization constant HA + H2O A- + H3O+ [A-] [H3O+] Equilibrium constant K = not for strong acids [HA] [H2O] Ka = K [H2O] = [A-] [H3O+] [HA] Acid ionization constant Ka < 1 - Log Ka = pKa Strong acid pKa < -2 / Weak acid pKa -2 to 12 Ka ↑ or pKa ↓ Stronger acid

pH and pOH pH = - log [H3O+] or -log [H+] pOH = - log [OH-] pH scale: Log 100 = 2 7 14 Acid Neutral Base [H3O+] ↑ [H3O+] ↓ and [OH-] ↑

pH and pOH H2O + H2O OH- + H3O+ KW = [H3O+] [OH-] = (1×10-7) (1×10-7) pH + pOH = 14

pH meter and pH indicators

Nature & pH indicators Bigleaf Hydrangea In basic soil (alkaline) In acidic soil

Acid Reactions 1. Reaction with metals (strong acids): a salt and H2 are produced. Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g) 2. Reaction with metal hydroxides: a salt and water are produced. KOH(aq) + 2HCl(aq) KCl(aq) + H2O(l)

Acid Reactions 3. Neutralization: reaction between an acid and a base. A salt and water are produced. KOH(aq) + 2HCl(aq) KCl(aq) + H2O(l) 2NaOH(aq) + H2SO4(aq) Na2SO4(aq) + 2H2O(l) Strong acid reacts with strong base to produce the weaker acid and weaker base. (This is the direction of a reaction)

Titration (Neutralization reaction) B A MB: known VB: known MA: unknown VA: known Equivalence point: Equal amount of acid (H+) and base (OH-) (pH = 7). 2NaOH + 1H2SO4  2NaSO4 + 2H2O MA × VA MB × VB = Coefficient A Coefficient B

Buffers pH stays constant. Buffer Acid or Base pH stays constant. Buffer A buffer resists changes in pH when limited amounts of acid or base are added.

Buffers Our blood is a buffer solution. pH of blood ≈ 7.4 Acid pH of blood ≈ 7.4 Acid Base Shock Absorber

Acetic acid / Sodium acetate Buffer Composition Weak Acid + its Conjugate base (in equilibrium) salt of the weak acid CH3COOH + CH3COO-Na+ CH3COOH / CH3COO- Acetic acid / Sodium acetate Acetic acid / Acetate ion pair

Buffers Carbonate buffer H2CO3 / HCO3- Phosphate buffer H2PO4- / HPO42- Proteins buffer

How do buffers work? HCO3- + H3O+ → H2CO3 + H2O Carbonate buffer H2CO3 / HCO3- If we eat an acidic food: HCO3- + H3O+ → H2CO3 + H2O H2CO3 + OH- → HCO3- + H2O If we eat a basic food:

Henderson-Hasselbalch equation pH of Buffers HA(aq) A-(aq) + H+(aq) Weak acid Conjugate base [A-] pH = pKa + log [HA] Henderson-Hasselbalch equation [HA]: concentration of the weak acid [A-]: concentration of its conjugate base pKa of the weak acid