Solubility and Concentration

Question 1

Solute, Solvent, like dissolves like

Answer 1

Solute
The substance being dissolved

Solvent
The substance doing the dissolving

“Like dissolves like”
Solutes dissolve in solvents of similar polarity
Polar or ionic solutes only dissolve in polar solvents
Non-polar solutes only dissolve in non-polar solvents

Question 2

How much solute is dissolved?

Answer 2

Chemists are often interested in quantifying how much solute is actually dissolved in the solvent
They do this using a ratio – the quantity of solute to the quantity of solution or solvent
This ratio is called concentration

high concentration- concentrated solution
low concentration - diluted solution

Question 3

Amount Concentration (formerly known as “molarity”)

Answer 3

Chemists find it most convenient to express solution concentrations in terms of the amount (in moles) of solute per liter of solution
amount concentration = amount of solute (in moles) / volume of solution (in L)
units of amount concentration are in Mol/L
c=n/v

Question 4

Is there a limit to how much solute you can dissolve in a particular solvent??

Answer 4

Yes there is! A solution that contains the maximum quantity of solute is called a saturated solution
The maximum concentration of a compound in a particular solvent (often water) is called its solubility

Question 5

Degrees of saturation

Answer 5

A solution that contains less than the maximum quantity of solute is an unsaturated solution

Under special circumstances, you can force a solution to dissolve more solute than it normally would – this is called a supersaturated solution!
More on this later

Question 6

Solubility depends on temperature

Answer 6

A solubility curve is a graph of the solubility of a given solute against temperature.

Question 7

Interpreting solubility curves

Answer 7

Above curve = supersaturated
on line= saturated
below curve = unsaturated

Question 8

How do we make a supersaturated solution?

Answer 8

A super saturated solution is prepared by dissolving the solute in water at a high temperature, then allowing the solution to cool

As the temperature drops, the solubility drops, but the extra solute doesn’t crystalize from the solution immediately – the solution becomes supersaturated

The extra solute stays dissolved until something disturbs the system
A tap on the flask or dropping a single crystal of solute into the solution can initiate crystallization!
The “seed crystal” provides a surface onto which excess solute can crystallize

Question 9

Solubility curves of gases

Answer 9

Unlike with solids, the solubility of gases decreases as the temperature rises

Question 10

Pressure also effects gas solubility!

Answer 10

Gases are significantly affected by changes in pressure (not so for solids & liquids)
The solubility of a gas in a liquid increases as the pressure of the gas is increased

Question 11

gas solubility: soda

Answer 11

This is why soft drinks bubble and fizz when they’re opened!
When you open the can/bottle, the pressure drops, so the CO2 comes out of solution, which results in bubbling/fizzing