III. Colligative Properties

III. Colligative Properties

Solutions I II III Colligative Properties Definition Colligative Property property that depends on the concentration of solute particles, not their identity

Types Freezing Point Depression (tf) f.p. of a solution is lower than f.p. of the pure solvent Boiling Point Elevation (tb) b.p. of a solution is higher than b.p. of the pure solvent

Types Freezing Point Depression Types Boiling Point Elevation Solute particles weaken IMF in the solvent. Types Applications salting icy roads making ice cream

antifreeze cars (-64C to 136C) fish & insects Calculations t = k (f or b) m i t: change in temperature (C) k: constant based on the solvent (Ckg/mol) m: molality (m) i: # of particles (vant Hoff factor) Calculations

# of Particles Nonelectrolytes (covalent) remain intact when dissolved 1 particle Electrolytes (ionic) dissociate into ions when dissolved 2 or more particles T = Kmi For covalent compounds, i = 1. For ionic compounds, i = the number of ions present (both + and -)

Compound Glycol NaCl CaCl2 Theoretical Value of i 1 2 3

Calculations At what temperature will a solution that is composed of 0.73 moles of glucose in 225 g of phenol boil? GIVEN: b.p. = 181.8C tb = ? kb = 3.60Ckg/mol m = 3.2m i=1 tb = kb m i

WORK: m = 0.73mol 0.225kg tb = (3.60Ckg/mol)(3.2m)(1) tb = 12C b.p. = 181.8C + 12C b.p. = 194C Calculations Find the freezing point of a saturated solution of NaCl containing 28 g NaCl in 100. g water. GIVEN:

f.p. = 0C tf = ? WORK: m = 0.48mol 0.100kg tf = (1.86Ckg/mol)(4.8m)(2) kf = 1.86Ckg/mol m = 4.8m i=2 tf = kf m i tf = 18C f.p. = 0.00C - 18C

f.p. = -18C K for Common Substances Substance Kb Substance Kf benzene 2.53 benzene

5.12 camphor 5.95 camphor 40. carbon carbon 30. 5.03 tetrachloride

tetrachloride 1.79 ethyl ether 2.02 ethyl ether 1.86 water 0.52 water

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