Chapter 15.6 Solubility

Question 1

Define solubility

Answer 1

Solubility refers to the maximum amount of solute that can be dissolved in a given amount of solvent (usually 100g) at a certain temperature.

Question 2

What does it mean if a solution is SATURATED?

Answer 2

A saturated solution is a solution which is unable to dissolve more solute into the mixture at the given temperature because it has reached it’s maximum solubility.

Question 3

What does it mean if a solution is UNSATURATED?

Answer 3

An unsaturated solution is a solution which can dissolve more solute into the mixture (at the given temperature) because it has not reached its MAXIMUM solubility.
(*contains less solute than is needed to make the solution saturated.)

Question 4

What does it mean if a solution is SUPERSATURATED?

Answer 4

A super saturated solution is one which is UNSTABLE because it contains more solute than an a SATURATED solution - dissolved more than MAX SOLUBILITY

If it is disturbed, some of the solute will separate from the solvent as a solid.

Will form crystals when cooled

Question 5

How can a SUPERSATURATED SOLUTION DISSOLVE more?

Answer 5

When water is heated, the molecules within it will expand allowing more space for the Solvent to ‘fit in’ - allowing to dissolve.

Question 6

What is crystallisation? What does it mean to Crystallise?

Answer 6

To CRYSTALLISE means to form solids.

CRYSTALLISATION from solutions occur when an unsaturated solution becomes saturated (when the solute is cooled) and solute crystals start to form.

Question 7

What are the methods of CRYSTAKISATION?

Answer 7

1. Evaporation
   - increase temperature (boiling off ) so that the solvent evaporated which decreases the amount of solvent available to dissolve the solute.
2. Cooling a solution
   - The increase in temperature = higher kinetic energy that allows the solvent molecules to more effectively break apart the solute molecules that are held together by intermolecular attractions.
   - as the solution cools, the solvent lacks in kinetic energy and can no longer hold all of the solute molecules, So they begin to leave the solution and form solid crystals.
3. By adding a seed Crystal
   Seed crystal = small piece of single crystal
   - allows the recrystallization process to occur by eliminating the need for random molecular collision or interaction

Question 8

What does a Solubility curve do?

Answer 8

The curve shows how much substances can be dissolved in a solvent (water) at a given temperature.

X = Temperature °C
Y = Solubility (g/100g)

• dot on the curve represents the maximum amount of solute that can be dissolved in 100g of water at a particular temperature
• therefore each dot represents a saturated solution
• any point below is an unsaturated solution
• any point above is a supersaturated solution.

Question 9

How does solubility of a gas become affected by temperature?

Answer 9

As the temperature increases in a solvent the less soluble it is for a Gas.

Increased temperature causes an increase in kinetic energy.
The higher kinetic energy causes more motion in gaseous molecules which can break intermolecular bonds and escape from solution.
Through bubbles of boiling water, gas can escape.