April 02, 2013 Solubility Guidelines When you write a dissociation equation or any equation involving ionic compounds, you need to know whether a compound is soluble in order to include the proper state - solid (s) or aqueous (aq) - in the equation. Determine the Solubility of the Following Compounds

Compound Soluble? (Y/N) Compound Soluble? (Y/N) KBr Yes ZBr (aq) Sodium Acetate Yes CH3COONa Zn(OH)2 No ZnS (s) MgCO3 No MgCO3 (s) Copper Sulphate No CuSO4 (s) BaSO4 No BaSO4 April 02, 2013

Solubility

The maximum amount of solute that can dissolve in a given amount of solvent at a given temperature

A saturated solution has the maximum amount of dissolved solute at a given temperature

An unsaturated solution can dissolve more solute at a given temperature

Solubility is usually expressed in g/100mL of solvent April 02, 2013

Every compound has a unique solubility in water

SOLUBILITY COMPOUND (g/100mL water)

glucose 45.0

codeine 0.79 (C18H21NO3

hexane (C6H14) 0.11

docosane 0.0000006 (C22H46) April 02, 2013 Example The solubility of sucrose is 67.1 g/100mL of water at 25.0℃ How much sucrose is dissolved in 250 mL of water?

To Solve, set up a ratio:

The solubility of sucrose is 67.1 g/100 mL of water at 25.0℃

How would you describe a solution that contained 300 grams of sucrose dissolved in 500 mL of water at 25℃? Is the solution saturated or unsaturated? April 02, 2013

Since this is less than the solubility of sucrose, the solution is unsaturated

Saturated Solutions Once a solution has reached the limit of solubility, the solution is said to be saturated -This means that the solvent can hold no more solute -If additional solute is added to a saturated solution, the extra solute will settle out. April 02, 2013

A saturated solution is in a state of equilibrium This means that : •the rate of dissolving is the same as the rate of crystallization (crystalizing is the reverse of dissolving)

•the mass of undissolved solute remains the same April 02, 2013

What mass of sucrose is in a beaker containing 100mL of saturated solution and 30.0g of undissolved solute?

Total mass =

Total mass =

Conditions of Equilibrium

The system must be closed (no matter can enter or leave)

There must be solid and solution in contact April 02, 2013

Dissolving:

CuSO4(s) -->

Crystallizing: --->

An equilibrium arrow can be used to represent an equilibrium process

Since we can't actually see molecules, we know that equilibrium happens because of a neat experiment involving radioactive iodine. April 02, 2013

Radioactive Iodine Solid NaI containing radioactive iodine was added to a saturated solution of NaI that wasn't radioactive

Over time, the radioactivity was found in the solution even though the same amount of solid remained at the bottom of the beaker

This indicated that dissolving was still taking place at the same rate of crystallization April 02, 2013 Factors That Affect Solubility A) Temperature

The solubility of most solids increases with

S

D temperature

I L Higher temperature makes it easier to

O S break the intermolecular forces between the solute and solvent

S

D The solubility of most liquids is NOT greatly I

U affected by temperature

Q

I

L