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Unformatted text preview: Colligative Properties Changes in colligative properties depend only on the number of solute particles present, not on the identity of the solute particles. These properties are called colligative: 1) vapor pressure lowering 2) boiling point elevation 3) freezing point depression 4) osmotic pressure 1 BoilingPoint Elevation with Solute The boiling point of a solvent containing a nonvolatile solute increases in proportion to the amount of solute present. m K T b b = T b = increase in boiling point K b = constant which depends on the identity of the solvent but not (in the simplest case) on the identity of the solute m = molality of the solution The increase in the boiling point is 2 1) The values of K b are quite dependent on the solvent. 2) T b can be expressed in units of K or o C, but to find T b in o F requires unit conversion. 3) The boiling point elevation depends on the molality m (mols solute / kg solvent) and therefore the number of mols solute dissolved. For a salt like NaCl in water, the number of mols dissolved is twice the number of mols added, because the added NaCl separates into Na + and Cl . m K T b b = 3 Find the boiling point in o C of 100 gm sucrose in 100 gm water. Sucrose is a disaccharide composed of glucose and fructose, and its molecular formula is C 12 O 11 H 22 . (a) Find the molar mass of sucrose. (b) Find the number of mols of sucrose. (c) Find the kg solvent. (d) Find the molality of the solution. (e) Find the new boiling point. 4 Find the boiling point in o C of 100 gm sucrose in 100 gm water. Sucrose is a disaccharide composed of glucose and fructose, and its molecular formula is C 12 O 11 H 22 . (a) Find the molar mass of sucrose. mol gm 342 ) 1 ( 22 ) 16 ( 11 ) 12 ( 12 = + + (b) Find the number of mols of sucrose. (c) Find the kg solvent. (d) Find the molality of the solution. (e) Find the new boiling point. 5 Find the boiling point in o C of 100 gm sucrose in 100 gm water. Sucrose is a disaccharide composed of glucose and fructose, and its molecular formula is C 12 O 11 H 22 . (a) Find the molar mass of sucrose. mol gm 342 ) 1 ( 22 ) 16 ( 11 ) 12 ( 12 = + + (b) Find the number of mols of sucrose. mol mol gm gm 292 . / 342 100 = (c) Find the kg solvent. (d) Find the molality of the solution. (e) Find the new boiling point. 6 Find the boiling point in o C of 100 gm sucrose in 100 gm water. Sucrose is a disaccharide composed of glucose and fructose, and its molecular formula is C 12 O 11 H 22 ....
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This note was uploaded on 09/13/2011 for the course CHEM 102 taught by Professor Todd during the Spring '08 term at UNC.
 Spring '08
 Todd
 Chemistry

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