solubility: the amount of solute needed to form a saturated solution in a given quantity of solvent under given conditions of T and P saturated: soln is in eq. w/undissolved solute unsaturated: more solute could dissolve supersaturated: the amount of dissolved solute exceeds the solubility -- soln has a clear, water-like appearance, but is VERY unstable addition of a seed crystal causes excess solute to crystallize, leaving a sat. soln. ( w /visible solid) i.e., there is solid at the bottom i.e., soln is clear ( MIGHT be colorless)

A supersaturated solution crystallizing upon the addition of a seed crystal. The resulting solution is then saturated.

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T ( o C) Solubility (g/100 g H 2 O) supersaturated unsaturated Sol. Curve for a Typical Substance Dissolved in a Liquid saturation limit (i.e., solubility) solid in liquid gas in liquid -- for solids, as T, sol. ___ -- for gases, as T, sol. ___

Factors Affecting Solubility Solute-Solvent Interactions -- As IMFs between solute and solvent increase, solubility _________. miscible: describes pairs of liquids that mix in all proportions (v. immiscible) increases Methanol, which is used to fuel race cars, is miscible with water due to its highly polar nature. –– –– ++ ++ ++

Low molar mass alcohols are completely miscible in water, due to H-bonding of hydroxyl group (–OH); as molar mass increases, the polarity of the alcohol molecule... decreases (it behaves more like a pure hydrocarbon) and miscibility decreases. -- Substances with similar IMFs tend to be soluble in one another; -- Some network solids aren’t soluble in either polar or non- polar solvents because of strong forces within the solid. e.g., CH 3 OH vs. CH 3 CH 2 CH 2 CH 2 OH “like dissolves like.” (pol/pol and np/np)

k = Henry’s law constant; it depends on solute, solvent, and temp. (M/pres. unit) Pressure Effects -- Pressure has no effect on the solubility of solids in liquids, but as P increases, gas solubility ___. -- Henry’s law:S g = k P g S g = solubility of the gas in the solution (M) P g = partial pressure of the gas over the solution (pres. unit) William Henry (1775 – 1836)

A bottled soft drink at 25 o C has CO 2 gas at a pressure of 5.0 atm over the liquid. If the partial pressure of CO 2 in the atmosphere is 4.0 x 10 –4 atm and the Henry’s law constant for CO 2 over water at 25 o C is 3.1 x 10 –2 M/atm, calculate the solubility of the CO 2 both before and after the bottle is opened. B E F O R E S g = 3.1 x 10 –2 M/atm (5.0 atm) = 0.16 M (fresh) A F T E R S g = 3.1 x 10 –2 M/atm (4.0 x 10 –4 atm) = 1.2 x 10 –5 M (flat) S g = k P g

Ways of Expressing Concentration qualitative: quantitative: concentrated v. dilute x 10 6 ppm = x 10 9 ppb = x ppt =

Unlike molarity, molality doesn’t change with temp. because... mass remains constant w / changing T. (V changes w /T.) To go between molarity and molality, you need… the soln’s density.

A 5.5-g sample of well water contains 0.75  g of lead ions. In ppm, find the concentration of lead ions. = 0.14 ppm The federal limit for lead in drinking water is 15 ppb. 140 ppb (!!!)

If a commercial bleach is 4.35% sodium hypochlorite by mass, calculate the bleach’s mole fraction and molality of the sodium hypochlorite. = mol NaClO = mol H 2 O = m = g NaClO g H 2 O g b l e a c h