Unformatted text preview: Apply the like-dissolves-like rule to determine if
like-dissolveseach vitamin is water soluble.
HO C HO C O VitaminVitamin-B2 C
CH 2 OH VitaminVitamin-C
C H VitaminVitamin-E H
CH2 CH2 CH CH3 CH3
2 CH2 CH CH2 CH2
2 CH2 CH
2 CH3 CH3 The stronger the attraction between solute and solvent
molecules, the higher the solubility. Water
Water Solubility of Solids
Solubility: Solute concentration in a saturated solution.
Water solubility of solids increases with temperature, but
pressure has little effect. Why?
Higher T Higher kinetic
energy of Molecules
• Break away from a solid.
• Mix with water molecules. Pressure cannot change
the definite volume of
solids / liquids. Most solids How to get a pure compound from a mixture on the basis of their
Suppose you have a sample of 90 g
KNO3 contaminated with 10 g NaCl,
how do you purify the sample? Fractional crystallization:
1. Dissolve sample in 100 mL of
water at 600C
2. Cool solution to 00C
3. All NaCl will stay in solution
(s = 34.2g/100g)
4. 78 g of PURE KNO3 will
precipitate (90 g – 12 g) = 78 g
(s = 12 g/100g). Water Solubility of Gases
Water solubility of gases decreases with temperature, but
increases greatly with pressure. Why?
Higher T Higher kinetic energy
of Molecules For most of gases Pressure forces gas molecules to
enter the solution
G as N2 S o lu b ility ( M ) 0 .6 9 × 1 0 -3
in w a ter CO O2 Ar Kr 1 .0 4 × 1 0 -3 1 .3 8 × 1 0 -3 1 .5 0 × 1 0 -3 2 .7 9 × 1 0 -3 Pressure & Solubility of Gases
Gas solubility in a liquid is directly
proportional to the partial pressure of
gas above the liquid when temperature
is held constant. S g a s = k ⋅ Pg a s
Sgas: gas concentration in a liquid;
Pgas: Partial pressure of gas;
k : Henry’s constant at certain T. Exercise
Exercise: Estimate the concentration of O2 in Siyuan lake
based on the data of solubility of gas...
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