Colligative properties 1 1. What does the phrase like dissolves like mean. 2. Why does the solubility of alcohols decrease with increased carbon chain length? Alcohol in water (mol/100g water) Methanol Ethanol Propanol Butanol 0.11 Pentanol 0.030 Hexanol 0.0058 Heptanol 0.0008 3. How does temperature affect solubility of solids? Of gases? 4. How does pressure affect solubility of solids? Of gases? 5. Look up the structures of vitamins A,B,C,D,E and K. Why are vitamins B and C water soluble and vitamins A,D,E and K are only soluble in fatty tissue. Why can taking too much supplements of vitamins A,D,E and K be harmful? DUE: Monday, December 16 (you can discuss together, but each person should write their own answer.)
Colligative properties 2 Concentration 1.A solution is made by dissolving 13.5 grams glucose (C 6 H 12 O 6 ) in 0.100 kg of water. What is the mass percentage of solute in this solution? 2. A 2.5 grams sample of ground water was found to contain 5,4 µg of Zn 2+. What is the concentration of Zn 2+ in ppm? 3. A commercial bleach contains 3.62 percent (by mass) sodium Hypochlorite, NaOCl. What is the mass of NaOCl in a bottle containing 2500 g bleaching solution? 4. A solution of HCl contains 36 % HCl ny mass. Calculate the mole fraction of Hcl in solution. Calculate the molality of the HCl. 5. Given the density of a solution of 5.0 grams tolulene(c 7 H 8 ) and 225 g benzene is 0.876 g/ml calculate a. molality b. molarity c. mass percent of solute Solutions
Colligative properties 3 1. Draw a diagram showing how NaCl dissolves 2. There are three things that will determine if a substance will dissolve and if it does, whether or not it does so endo or exothermically. 3. Why do polar solvents dissolve polar solutes and nonpolar solvents can t dissolve polar solutes. Example NaCl will dissolve in water but not gasoline 4. Is dissolving a chemical or physical change? Look at Ni in HCl and NaCl in H 2 O 5. Ways of measuring concentration a.
Colligative properties 4 b. c. d. e. f 1. 2. 3. 6. To convert between molarity and molality I need to know density of the solution. Explain to me how I can do this conversion. Give an example. Colligative Problems Colligative property: properties that depend on the quantity (concentration) of solute particles. Vapor Pressure Lowering What is vapor pressure? Example Explain the following situation. Ans: 23.2 torr Rauolt s Law P A = X A P A Example:Glycerin, C 3 H 8 O 3, is a nonvolatile nonelectrolyte with a density of 1.26 g/ml at 25 C. Calculate the vapor pressure at 25 C of a solution made by adding 50.0 ml of glycerin to 500.0 ml of water. The vapor pressure of pure water at 25 C is 23.8 torr.
Colligative properties 5 Note: just like ideal gases follow ideal gas laws at high temp and low pressure, Rauolt s law is based on ideal solutions. An ideal solution is one that have low concentrations and the solute and solvent molecules are similar in size and have similar intermolecular forces. If intermolecular forces between solvent and solute are weaker than between solvent and solvent and between solute and solute, than the vapor pressure tends to be greater than predicted by Raoult s law. Conversely, if the intermolecular forces between solute and solvent are greater, the vapor pressure will be lower than predicted by Raoult s law. WHY? Boiling point elevation 1.Why will adding solute to a solvent increase boiling point? 2. What will be its effect on a phase diagram? 3. ΔT b = K b m I Solvent Normal bp K b ( C/m) Normal fp K f ( C/m) ( C) ( C) Water 100.0 0.52 0.0 1.86 Benzene 80.1 2.53 5.5 5.12 Ethanol 78.4 1.22-114.6 1.99 Carbon 76.8 5.02-22.3 29.8 tetrachloride Chloroform (CHCl 3 ) 61.2 3.63-63.5 4.68 Example: Automotive antifreeze consists of ethylene glycol, (C 2 H 6 O 2 ) a nonvolatile nonelectrolyte. Calculate the boiling point and freezing point of a 25.0% mass solution of ethylene glycol in water. (ans: bp:102.8 C; fp: -10.0 C)
Colligative properties 6 Freezing point depression Why does adding solute decrease the freezing point? What will be its effect on the phase diagram? ΔT b = K b m I Example: List the following aqueous solutions in order of their expected freezing points: 0.050 m CaCl 2 ; 0.15 m NaCl; 0.10m HCl; 0.050 m HC 2 H 3 O 2 ; o.10 m C 12 H 22 O 11 Osmotic Pressure The pressure required to prevent osmosis is the osmotic pressure denoted by π. π = (n/v)rt = MRT where M is the molarity of the solution. Use the R constant to obtain the pressure in whatever units you choose. isotonic Two solutions of identical osmotic pressure, no osmosis will occur hypotonic: if one solution is of lower osmotic pressure, it is hypotonic with the more concentrated solution hypertonic the more concentrated solution is said to be hypertonic with respect to the dilute. 2. Example: What is the osmotic pressure at 20 C of a 0.0020 M sucrose(c 12 H 22 O 11 ) solution? Ans: 0.048 atm OR 37 torr.
Colligative properties 7 Determining Molar Mass A solution of an unknown nonvolatile nonelectrolyte was prepared by dissolving 0.250g in 40.0g CCl 4. The normal boiling point of the resultant solution was increased by 0.357 C. Calculate the molar mass of the solute. The osmotic pressure of an aqueous solution of a certain protein was measured in order to determine its molar mass. The solution contained 3.50 mg of protein dissolved in sufficient water to form 5.0 ml of solution. The osmotic pressure at 25 C was 1.54 torr. Calculate the molar mass of the protein.