Chapter 16 Acids and Bases Chemistry B2A

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 (If H 2 O is involved.)

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

HCl + H 2 O Cl - + H 3 O + Acids and Bases Proton (H + ) is transferred.

Acids and Bases C 6 H 5 OH + H 2 OC 6 H 5 O - + H 3 O + acidbase Conjugate base Conjugate acid Conjugate acid-base pair CH 3 COOH + NH 3 CH 3 COO - + NH 4 + acidbase Conjugate base Conjugate acid Conjugate acid-base pair

Acids and Bases Weak acid and 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 and 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 HCl(aq) + H 2 O(l) Cl - (aq) + H 3 O + (aq)

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 an 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

Acids and Bases Oxyacids: acidic H is attached to an oxygen atom. H 2 SO 4 H 3 PO 4 HNO 3 Organic acids: contain carboxyl group (-COOH). They are usually weak. CH 3 COOH

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

Ionization of water 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

[H + ] and [OH - ] [H + ] = [OH - ]Neutral solution [H + ] > [OH - ]Acidic solution [H + ] < [OH - ]Basic solution

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)

pH of strong acids HCl(aq) + H 2 O(l) Cl - (aq) + H 3 O + (aq) 0.10 M HCl  pH = ? 0.10 M HCl  0.10 M H + and 0.10 M Cl - [H + ] = 0.10 MpH = -log [H + ] pH = -log (0.10) = 1.00

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). NaOH + HNO 3  NaNO 3 + H 2 O M A × V A = M B × V B

Normality 2NaOH + 1H 2 SO 4  NaSO 4 + 2H 2 O Different coefficients Equivalent of an acid = amount of an acid that can furnish 1 mol of H + Equivalent of a base = amount of a base that can furnish 1 mol of OH - Equivalent weight of acid (base) = mass (g) of 1 equivalent of that acid (base). HCl1 equivalent HCl = 1 mole HCl equivalent weight HCl = 36.5 g NaOH1 equivalent NaOH = 1 mol NaOH equivalent weight NaOH = 40 g

H 2 SO 4 1 mol H 2 SO 4 = 2 mol H + 1/2 mol H 2 SO 4 = 1 mol H + 1 equivalent H 2 SO 4 = 1/2 mole H 2 SO 4 equivalent weight H 2 SO 4 = 98.0/2 = 49.0 g Normality H 3 PO 3 1 mol H 3 PO 3 = 3 mol H + 1/3 mol H 3 PO 3 = 1 mol H + 1 equivalent H 3 PO 3 = 1/3 mole H 3 PO 3 equivalent weight H 3 PO 3 = 82.0/3 = 27.3 g

Normality Normality = Number of equivalents Volume of solution (L) Neutralization: number of equivalents of an acid = number of equivalents of a base N A V A = the number of equivalents of an acid N B V B = the number of equivalents of a base N A × V A = N B × V B [H + ] = [OH - ]

Buffers acid or base Buffer pH stays constant. Equal molar amount of a weak acid and a salt of weak acid. Equal molar amount of a weak acid and its conjugate base. 1 mole CH 3 COOH + 1 mole CH 3 COONa 1 mole CH 3 COOH + 1 mole CH 3 COO -

Buffers pH of blood = between 7.35 and 7.45 Carbonate bufferH 2 CO 3 / HCO 3 - Phosphate bufferH 2 PO 4 - / HPO 4 2- Proteins buffer H 2 CO 3 + OH - → HCO H 2 O HCO H 3 O + → H 2 CO 3 + H 2 O

Buffers HA + H 2 O A - + H 3 O + Henderson-Hasselbalch equation: pH = pK a + log [A - ] [HA] If [AH] (weak acid) ≠ [A - ] (conjugate base) If [AH] (weak acid) = [A - ] (conjugate base) pH of buffer = pK a of weak acid