Chapter 9 Physical Properties of Solution PDF

CHAPTER 9: PHYSICAL PROPERTIES OF SOLUTION 49...

CHAPTER 9: PHYSICAL PROPERTIES OF SOLUTION 49 strong electrolytes – substances which completely dissociates into ions Solution: homogenous mixtures of two or more components that can be varied in composition e.g. salts, strong acids, strong bases Solvent: component present in greatest amount; substance in which a solute dissolves NaCl → Na+ (aq) + Cl- (aq) Solute: other components; substance that is dissolved Aqueous solutions: solution in which water is the solvent by ion-dipole interaction [ ions ― H2O (dipolar) ], the ions are stabilized by water Solvation: interaction between solute and solvent molecules; due to IMF; e.g. Na+ and Cl ion - molecules. H2O surrounded molecules surround the ions and hence these ions are dispersed uniformly throughout by H2O molecules the solution. Hydration: solvation when solvent is water weak electrolytes – substances which produce small amounts of ions; partially dissociated into ions Types of Solution e.g. weak acids, weak bases a. dilute – solution with low solute concentration CH3COOH ↔ CH3COO- (aq) + H+ (aq) b. concentrated – one with high solute concentration * CH3COOH ionizes to form CH3COO- abd H+. While this happens, some ions also combine to form solubility: maximum amount of solute that can be dissolved in a given amount of solvent back CH3COOH. This results to partial dissociation c. saturated solution – a solution that contains the maximum amount of solute the solvent can Nonelectrolytes – substances that does not dissociate into ions; form nonconducting solutions dissolves; no more solute can dissolve in it e.g. most molecular compounds are nonelectrolytes d. unsaturated solution – solution containing amount of solute less than its solubility; more solute can dissolve in it The Solution Process e. supersaturated solution – solution containing an amount of solute greater than the solubility; unstable solution A solute and solvent form a solution and both consist of particles attracting each other. For one substance to dissolves in another, three events must occur: Classification of Solutions Solute particles separate from each other: to overcome intermolecular interactions Solvent particles separates from each other: also involves overcoming intermolecular A. Based on elemental composition interactions Organic – compounds containing carbon (except CO2, CO, carbonates and cyanides) Solute and solvent particle mix: the particles attract each other Inorganic – compounds of the other elements including acids, bases, and salts B. Based on Ionization/Electrolytic Property of Solute Electrolytic property – the ability of the solution to conduct electricity Electrolytes – substances whose aqueous solutions contain ions and thus conduct electricity CHM018: Chemistry for Engineering Technologists Handout CHAPTER 9: PHYSICAL PROPERTIES OF SOLUTION 50 Ways of Expressing Concentration of Solutions where # of equivalents = 1. Mass percentage EW = = mass % of component = 2. Volume percentage a= = depends on the nature of the solute volume % of component = when the solute acts as a/an a. acids/base: a = number of replaceable H+ or OH- per mole of an acid/base 3. Parts per million, ppm (for very dilute solutions) e.g. HCl a = 1 eq/mol → EW = 36.46 g/eq H2SO4 a = 2 eq/mol → EW = 98.08 g/2 eq = 49.04 g/eq ppm component = = 1mg/kg solution = 1mg/ L NaOH a = 1 eq/mol solution Ba(OH)2 a = 2 eq/mol b. salts: a = total number of positive charge parts per billion, ppb = = μg/L solution e.g. KCl: K+ and Cl- a = 1 eq/mol 4. mole fraction, χ Ca(NO3)2: Ca 2+ and NO3 - a = 2 eq/mol c. reducing/oxidizing agent: a = total number of electrons gained or lost during redox reactions χ= e.g. C2O42- → CO2 a = 2 eq/mol MnO 4 - → Mn 2+ a = 5 eq/mol 5. Molality, m (does not vary with temperature) Relationship of Molarity and Normality m= (mol/kg) 6. Molarity, M M= ;N= hence, M= (mol/L) 7. Normality, N Dilution of Solution When a solution is diluted: N= (eq/L) the volume is increased by adding more solvent CHM018: Chemistry for Engineering Technologists Handout CHAPTER 9: PHYSICAL PROPERTIES OF SOLUTION 51 the concentration is decreased, and 9. How would you prepare 750-mL of 0.200 N of K2Cr2O7 (a = 3 eq/mol)? the total amount of solute remains constant 10. What volume of 0.125 N solution can be prepared from 15.0 g CuSO4? 11. Convert the following N to M: a. 4.0 N H3PO4 b. 5.0 N H2SO4 12. Convert the following molarity to normality: Dilution Formula: M1V1 = M2V2 a. 0.02 M H2SO4 where M1 ≡ initial concentration b. 0.50 M Na2CO3 M2 ≡ final concentration 13. What volume of 12.0 M HCl be used to prepare 300 mL of a 3.00 M solution? V1 ≡ initial volume 14. What is the concentration of 0.800L HNO3 solution prepared from 5.00 mL of 16.0 M HNO3? V2 ≡ final volume 15. What is the molality of a solution made by dissolving 36.5 g naphthalene, C10H8, in 420 g toluene, C7H8? Exercises 1. A solution contains 15.0 g NaCl in 100 g water. What is the percentage by weight of NaCl in the solution? Factors Affecting Solubility 2. A sample of vinegar is 5.00% acetic acid by weight. How much vinegar must you buy to have 1. Temperature 80.0 g acetic acid? Gases: increasing T, decreasing solubility 3. A commercial bleaching solution contains 3.62 mass % sodium hypochlorite, NaOCl. What is the Solids: increasing T, decreasing solubility mass of NaOCl in a bottle containing 2.50 g bleaching solution? 2. Nature of Solute and Solvent (Solute-Solvent Interactions) 4. What is the molality of a solution containing 0.850 g ammonia, NH3, in 125.0 g H2O? miscible liquids – pair of liquids that mix in all proportion, e.g. ethanol-H2O 5. Calculate the molality of an aqueous solution of NaCl of 0.250 kg of the solution contains 40.0g immiscible liquids – liquids that do not mix, e.g. oil-H2O NaCl? 6. Calculate the molarity of a solution prepared by dissolving 0.827 g NaCl in enough solvent to produce 250 mL of solution? “Like dissolves like” Substances with similar intermolecular attractive forces tend to be soluble in 7. How many grams of solid sample should be used to prepare a 500-mL 0.10 M NaOH solution, if the one another: polar ↔ polar nonpolar ↔ nonpolar solid is 95.0% pure NaOH? 8. Concentrated sulfuric acid solution has a density of 1.84 g/mL and contains 98.3% H2SO4 by 3. Pressure (for Gases) weight. increasing pressure, increasing solubility What is the molarity of this acid? Henry’s Law: Cg = k PgCg ≡ solubility of gas in solution CHM018: Chemistry for Engineering Technologists Handout CHAPTER 9: PHYSICAL PROPERTIES OF SOLUTION 52 K ≡ Henry’s law constant 2. Boiling Point Elevation Pg ≡ partial pressure of the gas over solution Because the vapor pressure of a solution is lower than that of the pure solvent at any temperature, a solution boils at a higher temperature than the pure solvent COLLIGATIVE PROPERTIES Raoult’s Law: “The elevation of the boiling point of a dilute nonvolatile solution is directly - properties that are dependent only on the concentrations of solute, not on the nature proportional to the molality of a non-electrolytic solutions.” - applicable only to non-volatile, non-electrolytic solutions Tb’ – Tb = ΔTb = Kbm 1. Vapor Pressure Lowering/Depression When a liquid is placed in a sealed container, a certain amount will evaporate as vapor to where ΔTb = boiling point elevation completely occupy the container. Kb = boiling point elevation constant; ebulioscopic constant The vapors exerts a pressure (vapor pressure) over the liquid Tb’ = boiling point of the solution The VP of a liquid depends on temperature: hi T → hi VP Tb = boiling point of pure solvent Addition of nonvolatile solute to a solvent reduces the capacity of the solvent molecules to m = molality of the solution evaporate (lower VP) Vapor pressure lowering α concentration of solute 3. Freezing Point Depression Since the vapor pressure of the solution is lower than that of the solvent at any RAOULT’S LAW – predicts the VP of solutions containing nonvolatile solutes temperature, the solution freezes at a lower temperature than the solvent PA = χA P A o PA ≡ VP of solution Raoult’s Law: “ The lowering of the freezing point of a dilute solution is directly proportional χA ≡ mole fraction of solvent to the molal concentration of the solution.” PAo ≡ VP of pure solvent Tf’ – Tf = ΔTf = Kfm where ΔTf = freezing point depression Ideal Solution – a solution that obeys Raoult’s Law; ideal behavior can at low solute concentration, Kf = freezing point depression constant; cryoscopic constant solute and solvent Tf’ = freezing point of the solution Tf = freezing point of the pure solvent Idea Solutions with two or more volatile components (A and B) m = molality of the solution PA = χ P A A o PB = χ P B B o → partial pressures of A and B PTOTAL = PA + PB Table of Constants: PTOTAL = χ P A A o +χPB B o Freezing Point, oC Kf, oC/m Boiling Point, oC Kb, oC/m CHM018: Chemistry for Engineering Technologists Handout CHAPTER 9: PHYSICAL PROPERTIES OF SOLUTION 53 Acetic Acid 16.6 3.90 118.1 3.07 T = absolute temperature Benzene 5.51 4.90 80.1 2.53 Water 0.00 1.86 100.0 0.512 When Papplied < π: osmosis takes place in the normal way and water moves through the membrane in CCl4 -22.8 31.8 76.8 5.03 the solution Ethanol -117.3 1.99 78.5 1.22 When Papplied > π: reverse osmosis occurs wherein water molecules move through the membrane from the solution to pure water. *Note: Reverse osmosis is employed in making freshwater from seawater, where the applied pressure is large enough to reverse the normal precess. Molecular Weight Determination DEFINITIONS: ΔTb = Kbm ΔTf = Kfm Isotonic Solutions – two solutions having the same osmotic pressure; equal concentrations Hypotonic Solutions – less concentrated solutions Hypertonic Solutions – more concentrated solutions Crenation – caused by movement of water from a (hypotonic) cell Hemolysis – caused by movement of water into a (hypertonic) cell Active transport – opposite of osmosis; movement of substances from a region of low concentration 4. Osmotic Pressure, π to a region of high concentration - pressure required to prevent osmosis from occurring Osmosis – net movement of solvent molecules from a region of low solute concentration to a region of high solute concentration through a semi-permeable membrane(allows selective passage of water molecules) π = MRT = where M = molarity R = gas constant = 0.0821 L·atm/K·mol CHM018: Chemistry for Engineering Technologists Handout CHAPTER 9: PHYSICAL PROPERTIES OF SOLUTION 54 CHM018: Chemistry for Engineering Technologists Handout