Chapter 8 Acids and Bases Chemistry B11

Acids and Bases Acids: sour Bases: bitter or salty

Acids and Bases NH 3 (aq) + H 2 O(l) NH 4 + (aq) + OH - (aq) Acid: produces H 3 O + Base: produces OH - Arrhenius definition: CH 3 COOH(aq) + H 2 O(l) CH 3 COO - (aq) + H 3 O + (aq) H 3 O + (Hydronium ion):H + (aq) + H 2 O(l) H 3 O + (aq) NaOH(s) Na + (aq) + OH - (aq) H2OH2O

Acids and Bases Acid: donates H + (proton) Bronsted and Lowry definition: (If H 2 O is not involved.) Base: accepts H + (proton) CH 3 COOH + NH 3 CH 3 COO - + NH 4 + acidbase Conjugate base Conjugate acid Conjugate acid-base pair

Acids and Bases HCl + H 2 O Cl - + H 3 O + acidbase Conjugate base Conjugate acid C 6 H 5 OH + H 2 OC 6 H 5 O - + H 3 O + acidbase Conjugate base Conjugate acid Conjugate acid-base pair

Acids and Bases Weak acid or base: is partially ionized in aqueous solution. CH 3 COOH(aq) + H 2 O(l)CH 3 COO - (aq) + H 3 O + (aq) Strong acid or base: is completely ionized in aqueous solution. HCl(aq) + H 2 O(l) Cl - (aq) + H 3 O + (aq) NaOH(aq) + H 2 O(l) Na + (aq) + OH - (aq) NH 3 (aq) + H 2 O(l) NH 4 + (aq) + OH - (aq) produces less H + and OH - produces more H + and OH -

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

Acids and Bases Monoprotic acids HCl Diprotic acids H 2 SO 4 Triprotic acids H 3 PO 4 Amphiprotic: it can act as either acid or a base. HCl(aq) + H 2 O(l) Cl - (aq) + H 3 O + (aq) NaOH(aq) + H 2 O(l) Na + (aq) + OH - (aq) base acid

Naming binary acids Hydro -ide ion -ic acid Anion : + HFF - : flouride ionHydroflouric acid HClCl - : chloride ionHydrochloric acid H2SH2SS 2- : sulfuride ionHydrosulfuric acid

Naming ternary acids Anion: -ite ion -ous acid -ate ion -ic acid HNO 3 NO 3 - :Nitrate ionNitric acid HNO 2 NO 2 - :Nitrite ionNitrous acid H 2 CO 3 CO 3 2- :carbonate ioncarbonic acid H 2 SO 3 SO 3 2- :sulfurite ionsulfurous acid

HA + H 2 O A - + H 3 O + Ionization constant K = [A - ] [H 3 O + ] [HA] [H 2 O] - Log K a = pK a not for strong acids K a ↑ or pK a ↓Stronger acid K a = K [H 2 O] = [A - ] [H 3 O + ] [HA] Acid ionization constant K a < 1 Equilibrium constant

pH and pOH pH + pOH = 14 H 2 O + H 2 O OH - + H 3 O + K W = [H 3 O + ] [OH - ] = (1×10 -7 ) (1×10 -7 ) [H 3 O + ] [OH - ] = 1×10 -14

pH and pOH pH = - log [H 3 O + ] or -log [H + ] pOH = - log [OH - ] 0 Acid Neutral Base 714 pH scale: [H 3 O + ] ↑[H 3 O + ] ↓ and [OH - ] ↑

pH meter and pH indicators

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

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

Acid Reactions 3. Neutralization: reaction between an acid and a base. A salt and water are produced. KOH(aq) + 2HCl(aq) KCl(aq) + H 2 O(l) 2NaOH(aq) + H 2 SO 4 (aq) Na 2 SO 4 (aq) + 2H 2 O(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) M B : known V B : known B A M A : unknown V A : known Equivalence point: Equal amount of acid (H + ) and base (OH - ) (pH = 7). 2NaOH + 1H 2 SO 4  2NaSO 4 + 2H 2 O M A × V A M B × V B = Coefficient A Coefficient B

Buffers Acid or Base Buffer pH stays constant. 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 Shock Absorber Acid Base

Buffer Composition Weak Acid + its Conjugate base (in equilibrium) salt of the weak acid CH 3 COOH + CH 3 COO - Na + CH 3 COOH / CH 3 COO -

Carbonate bufferH 2 CO 3 / HCO 3 - Phosphate bufferH 2 PO 4 - / HPO 4 2- Proteins buffer Buffers

How do buffers work? Carbonate bufferH 2 CO 3 / HCO 3 - If we eat an acidic food: HCO H 3 O + → H 2 CO 3 + H 2 O H 2 CO 3 + OH - → HCO H 2 O If we eat a basic food:

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