Solubility

Section 8.5

Solubility When we dissolve a solute in water, there is a point

where no more will dissolve

Saturated solution - a solution containing the maximum quantity of a solute at specific temperature and pressure conditions look for the presence of undissolved solids in the solution

Solubility – the concentration of a saturated solution of a solute at a specific temperature and pressure Units for solubility are usually grams of solute per 100

mL of solvent (g/100mL)

Unsaturated solution = a solution containing less than maximum quantity of a solute at specific temperature and pressure conditions

Supersaturated solution = a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances

Other Important Terms

Solubility

SATURATED SOLUTION

no more solute dissolves

UNSATURATED SOLUTIONmore solute

dissolves

SUPERSATURATED SOLUTION

becomes unstable, crystals form

increasing concentration

Solubility tables (pg. 324) ionic compounds are listed as having

either high or low solubility at SATP (25°C and 100 kPa)

anions paired with particular cations have either: High solubility OR Low solubility

Solubility Categories High solubility = with a maximum

concentration at SATP (standard ambient temperature and pressure) of greater than or equal to 0.1mol/L

Low solubility = with a maximum concentration at SATP of less than 0.1mol/L

Insoluble = a substance that has a negligible solubility at SATP

Solubility of Solids Solubility of a solid changes with

temperature Higher solubility at higher temperatures

in industry, the solute is isolated from many solutions by evaporating the solvent

this increases the concentration of a solution and once it is greater than the solubility, the solute crystallizes (precipitates) out

Solubility Curve = a graph of solubility versus temperature

Solubility Curve of Solids (pg. 394) Solubility is most

affected by temperature The line shows you how

much solute can dissolve in 100g of water at a particular temperature.

A concentration on the line is a saturated solution

Concentrations above the line are supersaturated

Concentrations below the line are unsaturated

What can I do with a solubility curve? Calculating the amount of

solute that needs to be added to a solution to make saturate it.

Calculating the amount of solute that will crystallize out of solution when the solution is cooled.

per100 gH2O

Classify as unsaturated, saturated, or supersaturated.

80 g NaNO3 @ 30oC unsaturated

45 g KCl @ 60oC saturated

50 g NH3 @ 10oC unsaturated

70 g NH4Cl @ 70oC supersaturated

So sat. pt. @ 40oC for 500 g H2O = 5 x 66 g = 330 g

120 g < 330 g unsaturated

saturation point @ 40oC for 100 g H2O = 66 g KNO3

Per 500 g H2O, 120 g KNO3 @ 40oC

(A) Per 100 g H2O, 100 g Unsaturated; all

soluteNaNO3 @ 50oC. dissolves; clear

solution.

(B) Cool solution (A) very Supersaturated; extraslowly to 10oC. solute remains in solution;

still clear.

Describe each situation below.

(C) Quench solution (A) in Saturated; extra solute an ice bath to 10oC. (20 g) can’t remain in

solution, becomes visible.

Solubility of Gases Gases have a higher solubility at lower

temperatures

Think: Pop glass of cola sitting in the refrigerator as

compared to one sitting on the kitchen counter

Can of pop is also stored under pressure Increased pressure = increased solubility

Solubility Graph

LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 517

0 10 20 30 40 50 60 70 80 90 100

Solubility vs. Temperature for Solids

Sol

ubili

ty (

gram

s of

sol

ute/

100

g H

2O)

KI

KCl

20

10

30

40

50

60

70

80

90

110

120

130

140

100

NaNO3

KNO3

HCl NH4Cl

NH3

NaCl KClO3

SO2

shows the dependence

of solubility on temperature

gases

solids

Solubility of Sodium Acetate

Temperature (oC)

025 50 75 100

Sol

ubili

ty(g

/100

g H

2O)

50

100

150Supersaturated

solution

Unsaturated solution

Saturated

Video Clip

Charles H.Corwin, Introductory Chemistry 2005, page 378

A single crystal of sodium acetate, NaC2H3O2, is dropped into a

supersatureated solution

The small crystal causes extensivecrystallization, and eventually

the solute forms a solid mass of NaC2H3O2.

Homework

Worksheet: Solubility Curves & Solubility Tables