Please Pick Up Electrolytes, Acids and Bases Problem Set General Solubilities of Common Compounds in Water Guidelines for Identifying Electrolytes and Nonelectrolytes Guidelines for Writing Net Ionic Equations Ionization Constants for Acids and Bases

Aqueous Equilibria Acids and Bases Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

6/22/2015 Electrolytes Reading Assignment: Zumdahl: Chapter 4.9, 7.1 The degree that a compound dissociates into ions is a measure of its strength, not its concentration. Strong electrolytes - dissociate virtually 100% into ions, at all concentrations Weak electrolytes - dissociate less than 50% into ions Non-electrolytes - do not form ions when dissolved in a solvent.

6/22/2015 Strong Electrolytes Strong Acids HCl, HBr, HI, HNO 3, H 2 SO 4, HClO 4, etc. Strong Bases Group IA hydroxides: NaOH, KOH Ca(OH) 2, Sr(OH) 2, Ba(OH) 2 Most ionic compounds

6/22/2015 Strong Electrolytes Soluble Salts Binary compounds of metal cations with nonmetal anions Compounds of metal cations with polyatomic anions Ammonium cation with nonmetal or polyatomic anions. Which of these are soluble, strong electrolytes? KCl, Zn(NO 3 ) 2, CuSO 4, NH 4 I

6/22/2015 Strong Electrolytes Slightly soluble salts Compounds which have a solubility product constant (K sp ) are strong electrolytes, but are not very soluble. AgCl, BaSO 4, Mg(OH) 2, etc.

6/22/2015 Weak Electrolytes Weak acids, weak bases, and other soluble compounds which do not ionize extensively. A weak electrolyte will usually have a dissociation constant associated with it such as K a or K b.

6/22/2015 Weak Electrolytes Weak Acids HCOOH, CH 3 COOH, HF, HCN, HNO 2, H 3 PO 4, H 2 S, HS –, H 2 CO 3, HCO 3 –, etc. Weak Bases NH 3, CH 3 NH 2, N 2 H 4, etc.

6/22/2015 Non-electrolytes  Compounds which dissolve but do not form a significant number of ions.  Most covalent compounds: compounds of two or more nonmetals excluding those which are strong or weak electrolytes. water, sugar, methanol, ethylene glycol, etc.

6/22/2015 Solubility is related to the concentration of the solute in the solvent Dissociation is related to the ability of the compound to form ions in solution

6/22/2015 Solubility is related to the concentration of the solute in the solvent Dissociation is related to the ability of the compound to form ions in solution Categorize each of the following compounds in terms of its solubility and tendency to form ions. oil NaCl sugar acetic acid Ca(OH) 2

6/22/2015 Electrolytic Character  Solubility Examples Oil -- not very soluble, doesn’t ionize NaCl -- very soluble and very conductive Sugar -- very soluble but non-conducting Acetic acid -- very soluble but poorly conducting Calcium hydroxide -- slightly soluble but the amount that dissolves, completely ionizes in water

6/22/2015 Solubility is related to the concentration of the solute in the solvent Dissociation is related to the ability of the compound to form ions in solution soluble slightly soluble strong weak non- electrolyte

6/22/2015 Electrolytic Character  Solubility Examples Sugar -- very soluble but non-conducting Acetic acid -- very soluble but poorly conducting Calcium hydroxide -- slightly soluble but the amount that dissolves, completely ionizes in water Oil -- not very soluble, doesn’t ionize

6/22/2015 Solubility is related to the concentration of the solute in the solvent Dissociation is related to the ability of the compound to form ions in solution soluble slightly soluble strong weak non- electrolyte oil NaClCa(OH) 2 sugar acetic acidCO 2 The solubility of a compound does not predict its electrolytic character.

6/22/2015 Equation Notation  Each compound in solution is considered in its “predominant” form with proper annotation: HCl(aq)H + (aq) + Cl – (aq) KOH (aq)K + (aq) + OH – (aq) Strong Electrolytes as completely dissociated.

6/22/2015 Equation Notation  Each compound in solution is considered in its “predominant” form with proper annotation: Weak Electrolytes and Non-electrolytes as molecular compounds HF(aq)H + (aq) + F – (aq) CH 3 OH (aq)H + (aq) + CH 3 O – (aq)

6/22/2015 Group Activity  Identify the predominant form and write a dissociation reaction for the following compounds nitric acid hydrofluoric acid potassium chlorate aqueous ammonia sodium hydroxide

6/22/2015 Equilibrium Arrows HNO 3 (aq)H + (aq) + NO 3 – (aq) HF(aq)H + (aq) + F – (aq) KClO 3 (aq)K + (aq) + ClO 3 – (aq) NH 3 (aq) + H 2 O (l)NH 4 + (aq) + OH – (aq) NaOH (aq)Na + (aq) + OH – (aq)

6/22/2015 Acidity versus Neutralizing Ability HCl(aq)H + (aq) + Cl – (aq) CH 3 COOH (aq)H + (aq) + CH 3 COO – (aq) HCl(aq) + OH – (aq)H 2 O (l) + Cl – (aq) CH 3 COOH(aq) + OH – (aq)H 2 O (l) + CH 3 COO – (aq) 0.1 M hydrochloric acid is more acidic than 0.1 M acetic acid, but the same volume of each can neutralize the same amount of base.

6/22/2015 Acid - Base Theories TheoryAcidBase ArrheniusH + donor OH – donor Brønsted- Lowry H + donorH + acceptor Lewis e – pair acceptor e – pair donor

6/22/2015 Conjugate Acids and Bases  The reaction of an acid and a base produces a conjugate acid and a conjugate base. HCl(aq) + OH – (aq)H 2 O(l) + Cl – (aq) acidbaseconjugate acid conjugate base

6/22/2015 Conjugate Acid-Base Pairs Acid Conjugate Base Conjugate Acid HCl NH 3 HCO 3 – CO 3 2 – H 2 CO 3 NH 3 NH 4 + Cl –

6/22/2015 Group Activity  Write an equation that demonstrates the acidic character of carbonic acid when it reacts with water. Assign appropriate equilibrium arrows for the reaction. Identify the acid and base. Identify the conjugate acid and conjugate base.

6/22/2015 Acid Character of Carbonic Acid H 2 CO 3 (aq) + H 2 O(l)H 3 O + (aq) + HCO 3 – (aq) acidbaseconjugate acid conjugate base Which is the acid, which is the base? Which way does the equilibrium arrow point? What are the products of this reaction?

6/22/2015 Group Activity  Determine how the bisulfide ion (HS – ) can behave as an acid in water. can behave as a base in water.  Write an equation for each reaction as it demonstrates its acid or base character.  If possible, assign appropriate equilibrium arrows for each reaction.

6/22/2015 Acid-Base Character of Bisulfide Ion HS – (aq) + H 2 O(l) acidbase H 3 O + (aq) + S 2 – (aq) HS – (aq) + H 2 O(l) baseacid OH – (aq) + H 2 S(aq) conjugate acid conjugate base conjugate base conjugate acid

6/22/2015 Group Activity  For each of the following species determine if it can behave as an acid. if it can behave as a base.  Write an equation for each species as it demonstrates its acidic or basic character.  If possible, assign appropriate equilibrium arrows for each reaction.

6/22/2015 Determine the Acid-Base Character H 2 CO 3 OH – K + F – HS – H 2 O NH 4 + SO 4 2 – Which of these species can act as an acid, which can act as a base, which can act as both? Write an equation that shows each character and justify your answer.

6/22/2015