Solubility: the amount of solute needed to form a saturated solution in a given quantity of solvent...

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Transcript of Solubility: the amount of solute needed to form a saturated solution in a given quantity of solvent...

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solubility: the amount of solute needed to form a saturated solution in a given quantity of solvent under given conditions of T and Psaturated: soln is in eq. w/undissolved soluteunsaturated: more solute could dissolvesupersaturated: the amount of dissolved solute exceeds the solubility-- -- soln has a clear, water-like appearance, butis VERY unstableaddition of a seed crystal causes excesssolute to crystallize, leaving a sat. soln. (w/visible solid)i.e., there is solid at the bottomi.e., soln is clear (MIGHT be colorless)A supersaturated solution crystallizingupon the addition of a seed crystal. Theresulting solution is then saturated.

http://www.youtube.com/watch?v=HnSg2cl09PI http://www.youtube.com/watch?feature=endscreen&v=yxi6nxAqyew&NR=1 T (oC)Solubility(g/100 g H2O)supersaturatedunsaturatedSol. Curve for a Typical SubstanceDissolved in a Liquidsaturation limit(i.e., solubility)solid in liquidgas in liquid -- for solids, as T , sol. ___ -- for gases, as T , sol. ___Factors Affecting SolubilitySolute-Solvent Interactions -- As IMFs between solute and solvent increase, solubility _________. miscible: describes pairs of liquids that mix in all proportions (v. immiscible) increasesMethanol, which is used to fuel race cars,is miscible with water due to its highlypolar nature.

ddd+d+d+Low molar mass alcohols are completely miscible inwater, due to H-bonding of hydroxyl group (OH);as molar mass increases, the polarity of the alcoholmolecule... decreases (it behaves more like a purehydrocarbon) and miscibility decreases.-- Substances with similar IMFs tend to be soluble in one another; -- Some network solids arent soluble in either polar or non- polar solvents because of strong forces within the solid.

e.g., CH3OH vs. CH3CH2CH2CH2OHlike dissolves like. (pol/pol and np/np)k = Henrys 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 ___.-- Henrys law:Sg = k PgSg = solubility of the gas in the solution (M)Pg = partial pressure of the gas over the solution (pres. unit)William Henry(1775 1836)

A bottled soft drink at 25oC has CO2 gas at a pressureof 5.0 atm over the liquid. If the partial pressure of CO2in the atmosphere is 4.0 x 104 atm and the Henryslaw constant for CO2 over water at 25oC is3.1 x 102 M/atm, calculate the solubility of the CO2both before and after the bottle is opened.BEFORESg = 3.1 x 102 M/atm (5.0 atm)= 0.16 M(fresh)AFTERSg = 3.1 x 102 M/atm (4.0 x 104 atm)= 1.2 x 105 M(flat)Sg = k Pg

Ways of Expressing Concentration qualitative:quantitative:concentrated v. dilute

x 106ppm =x 109ppb =x 1012ppt =

Unlike molarity, molality doesntchange with temp. because...mass remains constant w/changing T.(V changes w/T.)To go between molarity andmolality, you needthe solns density.

A 5.5-g sample of well water contains 0.75 mg oflead ions. In ppm, find the concentration of lead ions.

= 0.14 ppmThe federal limit for lead indrinking water is 15 ppb.

140 ppb(!!!)

If a commercial bleach is 4.35% sodium hypochloriteby mass, calculate the bleachs mole fraction andmolality of the sodium hypochlorite.

= 0.05839 mol NaClO= 5.3139 mol H2O

= 0.610 m= 0.01094.35 g NaClO95.65 g H2O100 gbleach