Properties of Solutions (electrolytes) Chapter 4.1. Solution process (energy changes)

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1 Chapter 13 SOLUTIONS Properties of Solutions (electrolytes) Chapter 4.1 Solution process (energy changes) Solubility saturation supersaturation Factors that affect solubility intermolecular interactions (like dissolves like) temperature pressure Mary J. Bojan Page 1 BLB Chapter 13

2 SOLUTIONS Homogeneous mixture: Solute: Solvent: Aqueous solutions: Mary J. Bojan Page 2 BLB Chapter 13

3 Which Bulbs Light Up? Distilled H 2 O Bulb Wattage Tap H 2 O NaCl(aq) 1M HCl(aq) 1M CH 3 COOH sugar(aq) CH 3 OH For bulb to light, some minimum amount of current is needed. amount of current is related to the CONDUCTIVITY of the solution. CONDUCTIVITY: ability to conduct electricity Mary J. Bojan Page 3 BLB Chapter 13

4 Electrolytes A substance that conducts electricity when dissolved in solution Strong completely ionized (in solution) Good conductors NaCl(s) + H 2 O Na + (aq) + Cl (aq) + H 2 O HCl(aq) + H 2 O H 3 O + (aq) + Cl (aq) Weak partially ionized (in solution) Poor conductors NH 3 (aq) + H 2 O NH 4 + (aq) + OH (aq) CH 3 COOH(aq)+H 2 O CH 3 COO (aq)+h 3 O + (aq) Nonelectrolytes not ionized in solution Non-conductors C 6 H 12 O 6 (s)+h 2 O C 6 H 12 O 6 (aq)+ H 2 O glucose Mary J. Bojan Page 4 BLB Chapter 13

5 Identifying an electrolyte A) Is the compound ionic or molecular? Ionic: it is a strong electrolyte Note: it could be insoluble Molecular??? B) If it is molecular, is it an acid or a base? Yes: it is a strong or weak electrolyte No: it is a non electrolyte. Examples of electrolytes (strong or weak) Acids donate H + (aq) Bases accept H + (aq) Salts formed by replacing one or more H + of an acid with another cation Examples of non-electrolytes: Alcohols Carbohydrates (sugar) Aldehydes, ketones Mary J. Bojan Page 5 BLB Chapter 13

6 Ionic compounds: a compound that consists of positive and negative ions. Metal + nonmetal (usually) Eg. NaCl K 2 SO 4 Mg(NO 3 ) 2 NH 4 Cl Ionic compounds have high melting points and are brittle. Molecular compounds: compounds consisting of individual molecules All nonmetals or nonmetals and metalloids. Eg. HCl H 2 O CH 3 COOH NH 3 Molecular compounds usually have low melting points Mary J. Bojan Page 6 BLB Chapter 13

7 Difference between strong and weak electrolytes Assume all salts are strong electrolytes. Memorize strong acids and bases (Table 4.2) If a compound is an acid or a base, but NOT one of the strong acids or bases, then it MUST be a weak electrolyte. Common misconception: Electrolytes are ionic compounds NOT TRUE Strong electrolytes ionic or molecular compounds that ionize completely in solution. Weak electrolytes molecular compounds that are partially ionized in solution. Nonelectrolytes molecular compounds that do not ionize in solution Mary J. Bojan Page 7 BLB Chapter 13

8 These are all water soluble compounds. Are they strong, weak or non electrolytes? HCl NaCl CH 3 OH CH 3 COOH (acetic acid) Use Flowchart NH 3 Fe(NO 3 ) 2 Ca(OH) 2 Mary J. Bojan Page 8 BLB Chapter 13

9 Water soluble Compound molecular ionic Is it an acid? Yes No Strong electrolyte Is it a strong acid? Is it a molecular base? (eg. NH 3 ) Yes no Strong Electrolyte weak electrolyte yes no weak electrolyte non electrolyte Mary J. Bojan Page 9 BLB Chapter 13

10 Solution Process 1. break solute-solute interactions 2. break solvent-solvent interactions COSTS ENERGY 3. solute-solvent interactions form ENERGY IS RELEASED Processes occur spontaneously when: energy is released (exothermic) disorder increases (increase in entropy) These are linked: a process can be endothermic when the increase in entropy (disorder) is large enough. Mary J. Bojan Page 10 BLB Chapter 13

11 solvent Solute + dissolve!!!!" solution Solvent! """" " crystallize When rates are equal DYNAMIC EQUILIBRIUM Saturated solution: solute Supersaturated solution: Mary J. Bojan Page 11 BLB Chapter 13

12 Is the dissolution of CH 3 COONa (sodium acetate) exothermic or endothermic? 1. exothermic 2. endothermic Mary J. Bojan Page 12 BLB Chapter 13

13 SOLUBILITY FACTORS THAT AFFECT SOLUBILITY Temperature Effect of Temperature on solubility of ionic solids Effect of temperature on solubility of gases Type of intermolecular interactions and their strengths Pressure (LIKE DISSOLVES LIKE) Mary J. Bojan Page 13 BLB Chapter 13

14 In general: like dissolves like polar solvents dissolve polar (and ionic solutes) nonpolar solvents dissolve non-polar solutes If intermolecular forces broken and formed are ~ the same, dissolution is probable. Which one of the following will be most soluble in benzene (C 6 H 6 (l))? 1. H 2 O(l) 2. CH 3 OH(l) 3. HCl(l) 4. CH 3 CH 2 OH(l) 5. heptane Mary J. Bojan Page 14 BLB Chapter 13

15 Like dissolves like Alcohol solubility in water at 25 C (g/100g of H 2 O) CH 3 OH total CH 3 CH 2 OH total CH 3 CH 2 CH 2 OH total CH 3 CH 2 CH 2 CH 2 OH 8.06 CH 3 CH 2 CH 2 CH 2 CH 2 OH 2.82 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 OH 0.62 As length of hydrocarbon chain increases, solubility of alcohol in water decreases. Mary J. Bojan Page 15 BLB Chapter 13

16 Effect of pressure on Gas solubility. Increase P solute (gas); increase solubility Decrease P solute (gas); decrease solubility HENRY S Law is the relationship between solubility and pressure C g P g C g = k P g amount of gas dissolved (C g ) is proportional to the partial pressure of that gas (P g ) above the solution. Mary J. Bojan Page 16 BLB Chapter 13

17 Ammonia Fountain NH 3 gas H 2 O + phenolphthalein (pink in base) Mary J. Bojan Page 17 BLB Chapter 13

18 To increase the solubility of N 2 in water 1. increase T 2. decrease T 3. increase P 4. decrease P How will the solubility of KClO 3 be effected by an increase in pressure? 1. increase solubility 2. decrease solubility 3. no effect on solubility Mary J. Bojan Page 18 BLB Chapter 13

SOLUTIONS. SOLUTIONS: start with definitions

SOLUTIONS. SOLUTIONS: start with definitions SOLUTIONS Properties of Solutions (electrolytes) Chapter 9.1 Concentration (Section 9.5, 13.3) molarity M mass % % mole fraction X i ppm molality m Solution process (energy changes) Solubility Saturation