Solubility

Honors ChemistryMrs. Jacobus

Components of a Solution Solute is the substance being dissolved – powder Solvent is the dissolving agent – water

Solute

SolventDissolve

SolubilityThe amount of solute that will dissolve in a given amount of solvent.

Soluble vs. insoluble May vary with solvent

“Like dissolves like”

Polar and Nonpolar• A polar bond is a covalent bond between two

atoms where the electrons forming the bond are unequally distributed

• A nonpolar bond is a covalent bond between two atoms where the electrons forming the bond are equally distributed

Nonpolar Molecule (CH4) Polar Molecule (H2O)

“Like dissolves like”

Two substances with similar intermolecular forces (force between two molecules) are likely to be soluble in each other.

• non-polar molecules are soluble in non-polar solvents

CCl4 in C6H6

• polar molecules are soluble in polar solvents

C2H5OH in H2O

• ionic compounds are more soluble in polar solvents

NaCl in H2O or NH3 (l)

12.2

Factors Affecting Solubility– Temperature – Pressure

Solubility is the amount of solute that will dissolve in a given amount of solvent at a given temperature or pressure.

Factors Affecting the Rate of Dissolution

– Stirring– Temperature– Particle size/Surface

area

A saturated solution contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature.

An unsaturated solution contains less solute than the solvent has the capacity to dissolve at a specific temperature.

A supersaturated solution contains more solute than is present in a saturated solution at a specific temperature.

Sodium acetate crystals rapidly form when a seed crystal isadded to a supersaturated solution of sodium acetate.

12.1

Solubility

Concentration UnitsThe concentration of a solution is the amount of solute present in a given quantity of solvent or solution.

Percent by Mass

% by mass = x 100%mass of solutemass of solute + mass of solvent

= x 100%mass of solutemass of solution

12.3

Mole Fraction (X)

XA = moles of Asum of moles of all components

Concentration Units Continued

M =moles of solute

liters of solution

Molarity (M)

Molality (m)

m =moles of solute

mass of solvent (kg)

12.3

What is the molality of a 5.86 M ethanol (C2H5OH) solution whose density is 0.927 g/mL?

m =moles of solute

mass of solvent (kg)M =

moles of solute

liters of solution

Assume 1 L of solution:5.86 moles ethanol = 270 g ethanol927 g of solution (1000 mL x 0.927 g/mL)

mass of solvent = mass of solution – mass of solute= 927 g – 270 g = 657 g = 0.657 kg

m =moles of solute

mass of solvent (kg)=

5.86 moles C2H5OH

0.657 kg solvent= 8.92 m

12.3

Saturated, Unsaturated & SupersaturatedEx.1) If 10.0 g of KCl is dissolved in 100.0 g of water at

20.0oC, then would the solution be described as unsaturated, saturated, or supersaturated? ________________________________________.

Ex.2) If 10.0 g of KClO3 is stirred into 100.0 g of water at 20.0oC, then would the solution be described as unsaturated, saturated, or supersaturated? ________________________________________.

Ex.3) If 10.0 g of KClO3 is dissolved in 100.0 g of water at 20.0oC, then would the solution be described asunsaturated, saturated, or supersaturated? ________________________________________.

unsaturated

saturated with about 1 g of undissolved KClO3

supersaturated

Saturated, Unsaturated & SupersaturatedEx.4) If 100.0 g of KI is stirred into 100.0 g of water at

20.0oC, then would the solution be described as unsaturated, saturated, or supersaturated? ______________________________________

Ex.5) If 100.0 g of KNO3 is stirred into 100.0 g of water at 60.0oC, then would the solution be described as unsaturated, saturated, or supersaturated? ______________________________________

Ex.6) How many grams of KNO3 will exactly saturate 200.0 g of H2O at 20.0oC? ______________ g

unsaturated

unsaturated

≈70

Temperature and Solubility

Solid solubility and temperature

solubility increases with increasing temperature

solubility decreases with increasing temperature

12.4

Temperature and Solubility

O2 gas solubility and temperature

solubility usually decreases with increasing temperature

12.4

Watch the following video: http://www.youtube.com/watch?v=XSGvy2FPfCw

What kind of a solution is it?

Need more help?

• http://www.wwnorton.com/college/chemistry/gilbert2/tutorials/interface.asp?chapter=chapter_04&folder=saturated_solutions– Norton tutorial on solubility

• http://www.youtube.com/watch?v=zjIVJh4JLNo&edufilter=d3ViuWqXvxQy1rRgssBz8Q– Basic solubility

• http://www.youtube.com/watch?v=4VltXjR64SU&edufilter=d3ViuWqXvxQy1rRgssBz8Q– Molarity vs. Molality