Unformatted text preview: mount of so lute in a solut ion. DTf = m Kf
DTf = freezing po int depression Kf = freezing po int depression constant m = mo lalit y o f so lution Example 1: A so lut ion of antifreeze contains 135 g of ethylene glyco l (C H O ) per 500. g of water. 2 6 2 What is the freezing point of this so lut ion? (K =1.86 ºC/m) f Example 2: A so lut ion is prepared by disso lving 215 g of methano l (CH OH) in 800. g of water. 3 What is the freezing point of this so lut ion? (K =1.86 ºC/m)
f 5 Chemistry 52 Chapter 14 COLLIGATIVE PROPERTIES Boiling Point Elevation
· Addit io n of a nonvo lat ile so lute to a solvent increases its bo iling point.
· This bo iling point elevat ion is proportional to the amount of so lute in a so lut ion. DTb = m Kb
DTb = bo iling point elevat ion Kb = bo iling po int elevation constant m = mo lalit y o f so lution Example 1: What is the bo iling point of the antifreeze so lut ion in the previous problem? K2 = 0.512 °C/m OSMOSIS
· The movement of water into and out of the cells of plants as well as our bodies is an important bio logical process. This process is called osmosis.
· During osmosis, the solvent (water) moves through a semipermeable membrane (cell walls) fro m a solution that has a lower concentration of solute, to a solutio n that has a higher concent ration of so lute.
· This movement happens in a direct ion that attempts to equalize the concentrations of both sides. 6 Chemistry 52 Chapter 14 OSMOTIC PRESSURE
· As a result of this movement, the level o f the solut ion rises unt il it is balanced by the force of gravit y. The pressure that prevents the flow of so lution backwards is called osmotic pressure.
· The osmotic pressure depends on the number of solute particles in the so lut ion.
· Osmotic pressure is a co lligative property.
· Pure water has no osmotic pressure. The greater that number of solute particles in a so lution, the higher its osmotic pressure. · In the body, solut ions that have the same osmolarity as cells and therefore cause no osmotic pressure are called isotonic solut ions. · Solutions with osmolarity and osmotic pressure lower than the cells are called hypotonic solut ions.
· Solution wit h osmolarity and osmotic pressure greater than cells are called hypertonic solut ions. Example: Determine the tonicit y o f each of the fo llowing solutions. Cells have an ion concentration of 0.30 M. 0.15 M NaCl 0.15 M MgCl2 0.20 M glucose 7 Chemistry 52 Chapter 14 COLLIGATIVE PROPERITES OF IONIC SOLUTIONS
· When evaluat ing co lligative properties of ionic solutions, the total concentration of the ions must be considered.
· The number of ions produced from each formula unit is designated (i). –
NaCl ® Na+ + Cl i = 2 2
MgCl2 ® Mg + + 2 Cl i = 3 · The colligat ive properties of ionic so lut ions can be calculated with the fo llowing modifications: DTb = i m Kb
DTf = i m Kf Examples: 1. Calculate the freezing point of 0.010 m so lut ion of aluminum sulfate, Al2(SO4)3 . (Kf for water = 1.86 m/°C) Al2(SO4)3 ®
DTf = Tf = 2. Which of the following so lut ions will have the lowest freezing point? 0.15 m NaCl 0.25 m C6H12O6 0.10 m Fe(NO3)3 8...
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This document was uploaded on 09/19/2013.
- Fall '13