Unit 12 Acids Bases and Salts Properties of

Unit 12: Acids, Bases, and Salts

Properties of Acids • Taste sour • Are electrolytes: substances that produce ions in solution and as a result conduct electricity • Strong acid strong electrolyte • Weak acid weak electrolyte • Will react with active metals (above H 2) to produce H 2(g)

Review of Naming Rules: from Unit 5! • Binary Acids: ▫ hydro_______ic acid • Ternary Acids (use Table E) ▫ ate ic ▫ ite ous

Properties of Bases • Strong bases consist of a Group 1 or Group 2 metal w/ hydroxide ion • Taste bitter, feel slippery • Also electrolytes • Strong bases strong electrolytes • Weak bases weak electrolytes • Will NOT REACT with active metals

Look on RT for common acids and bases

Electrolytes • Form ions in water • Conduct electricity Salts • Ionic Compounds • M to NM Acids • p. H < 7 • H+ > OH- Bases • p. H > 7 • OH- > H+ Molecules (NM to NM) are NOT electrolytes…do NOT produce ions in solution!!

Indicators- Table M • Below the range the color is given on the left • Above the range the color is given on the right.

Arrhenius Theory of Acids and Bases Arrhenius Acid Arrhenius Base A substance, that when dissolved in water, produces H+ ions as the only positive ions in solution A substance, that when dissolved in water, produces OH- ions as the only negative ions in solution HCl (aq) H+ (aq)+ Cl- (aq) Na. OH (aq) Na+ (aq) + OH- (aq) known as a hydrogen ion known as a hydroxide ion

Bronsted-Lowry Theory of Acids and Bases ***based on the proton (H+) Bronsted Acid A proton donor Bronsted Base A proton acceptor Must release an H+ (aq) Does not need to have the ion OH-(aq) ion, but MUST have a lone pair of electrons. Ex) HCl (aq) Ex) NH 3 (aq)

Reversible Acid-Base Rxns Acid-Base reactions can be reversible! H 2 SO 4(aq) + NH 3(aq) B. A. B. B. HSO 4 -(aq) + NH 4+(aq) B. B. B. A. • A conjugate acid-base pair consists of two substances related by the loss or gain of a single hydrogen ion (H+) • Strong acids have weak conjugate bases • Strong bases have weak conjugate acids

Amphoteric Substances • A substance that can act as both an acid and a base is said to be amphoteric Ex) HCO 3 - (aq) + H 2 O (l) CO 32 - (aq) + H 3 O+(aq) **Here, HCO 3 - acts as an acid Ex) HCO 3 - (aq) + H 2 O (l) H 2 CO 3 (aq) + OH- (aq) **Here, HCO 3 - acts as a base Water is a common amphoteric substance- can act as both an acid and base

Lewis Definition of Acids and Bases Lewis Acid • an electron pair ACCEPTOR Lewis Base • An electron pair DONOR Ex) NH 3 + HCl NH 4+ + Cl-

Strengths of Acids and Bases • STRONG acids/bases dissociate completely in solution HCl(aq) H+(aq) + Cl-(aq) • Ka = [H+] [Cl-] = very large [HCl] STRONG acids have large Ka’s

Strength of acids and bases CH 3 COOH(aq) CH 3 COO-(aq) + H+(aq) • Ka = [CH 3 COO-] [H+] = very small (less than 1) [CH 3 COOH] • Not a lot of H+, therefore, weak acid • weak acids have small Ka’s

MEMORIZE STRONG ACIDS Weak acids • • CH 3 COOH (vinegar) • H 3 PO 4 • HF HI HBr HCl HNO 3 H 2 SO 4 HCl. O 4 • Strong acids have weak conjugate bases

MEMORIZE STRONG BASES Weak bases • Any group 1 or group 2 metal with OH- • NH 3 • Strong bases have weak conjugate acids

• For diprotic and triprotic acids, the H+’s come off in steps. It is more difficult to remove subsequent H+’s. • Ex. Ka • H 3 PO 4 H+ + H 2 PO 410 -3 • H 2 PO 4 - H+ + HPO 4 -2 10 -8 • HPO 42 - H+ + PO 4 -3 10 -13

Water as an Acid/Base • Water molecules undergo self-ionization H 2 O(l) + H 2 O (l) H 3 O+ (aq) + OH- (aq) • In pure water, the equilibrium concentration of [H 3 O+] = [OH-] = 1 x 10 -7 M • In other words, a neutral solution has the same number of moles of H+ ions as OH- ions.

“See-Saw Diagram” • Ion-Product Constant for Water (for aqueous solutions) Kw= [H+] x [OH-] = 1. 0 x 10 -14 ** exponents always add to 14

The p. H scale • Scale is based on the concentration of H+ ions in aqueous solution p. H = - log [H+] p. H < 7, acidic p. H = 7, neutral p. H > 7, basic

Determining p. H given concentrations [H+] = 1. 0 x 10 -6 M p. H = 6 • [OH-] = 1. 0 x 10 -8 M p. OH = 8 p. H + p. OH ALWAYS equals 14

The p. H scale is logarithmic • An increase in one unit of the p. H scale represents a ten-fold decrease (x 10) in the H+ ion concentration

Practice • p. H 6 to p. H 4 ▫ [H+] increases by a factor of 100 • p. H 5 to p. H 6 ▫ [H+] decreases by a factor of 10 • p. H 2 to p. H 4 ▫ [H+] decreases by factor of 100

p. H of weak acids Q. What is the p. H of 0. 10 M CH 3 COOH? CH 3 COOH(aq) H+(aq) + CH 3 COO-(aq) 0. 10 M – x x x Ka= [H+] [CH 3 COO-] = X 2 = 1. 8 x 10 -5 [CH 3 COOH] 0. 10 -x x 2 = 1. 8 x 10 -5 Very small. Ignore if 5% or 0. 10 -x less dissociation x 2= 1. 8 x 10 -5(0. 10) 0. 10 M HCl p. H=1 2 -6 x = 1. 8 x 10 0. 10 M CH 3 COOH p. H=2. 9 x= 1. 3 x 10 -3 p. H= -log(1. 3 x 10 -3)= 2. 9

Neutralization Reactions • Neutralization occurs when an acid and a base react to form a salt and water Acid + Base salt + water HCl (aq) + Na. OH (aq) Na. Cl (aq) + H 2 O (l) Acid Base Salt Water Net Rxn: H+ (aq) + OH- (aq) H 2 O (l)

Titrations • Used to determine the concentration of an acid or base • The equivalence point is reached when the moles H+ = moles OH • Titration Equation: M a Va = M b Vb ** Can use any unit of volume as long as you are consistent

unknown volume, unknown concentration Known volume, known concentration

Indicators for Titrations • Phenolphthalein is used to approximate the endpoint of a titration. • Colorless indicates an acidic solution and pink indicates a basic solution • When a pale pink color persists, the endpoint has been reached • The endpoint, or equivalence point, is when moles H+ = moles OH- (p. H =7)

Warm-Up What is the p. H of a 0. 025 M solution of Ca(OH)2? What is the hydroxide ion concentration of a 0. 0001 M solution of HNO 3 (aq)? What is the p. H of a 0. 220 M solution of hydrofluoric acid? (Assume 3% dissociation)

Hydrolysis (reverse of neutralization) • The process in which ions of a salt react with water to produce an acidic or basic solution is called hydrolysis

Examples Example Na. Cl Neutral Na. CH 3 COO Basic Parent Base Na. OH strong Parent Acid HCl strong CH 3 COOH weak NH 4 NO 3 NH 4 OH HNO 3 NH 4 NO 2 NH 4 OH HNO 2 Acidic p. H? Depends on Ka/Kb values weak strong weak

Salt formed from p. H SB SA neutral SB WA More than 7 WB SA Less than 7 WB WA ? Need Ka/Kb

Basic Anhydrides • Group I and II metal oxides that can react with water to form basic solutions. • Ex. Na 2 O(s) + H 2 O(l) 2 Na. OH(aq) Basic anhydride

Acid Anhydrides • Non-metal oxides that can react with water to form acidic solutions • Produce acid rain • Ex. SO 3(g) + H 2 O(l) H 2 SO 4(aq) • Ex. N 2 O 5(g) + H 2 O(l) 2 HNO 3(aq) • Ex. CO 2(g) + H 2 O(l) H 2 CO 3(aq)

Chemistry of Dyeing Eggs • https: //www. youtube. com/watch? v=l. MQ_qh. Ee yl 8