Solutions and Solubility

Question 1

Solubility

Answer 1

The maximum amount of solute that can be dissolved in a given quantity of a solvent at a given temperature.

Question 2

Rate of dissolving

Answer 2

The speed at which the solute
dissolves in a solvent

Question 3

Factors affecting the rate of dissolving

Answer 3

1. Increasing the surface area of the solute by crushing it.
2. Heating increases the kinetic energy of the solvent therefore, the speed of motion of the solvent molecules. This leads to a higher collision frequency. The solvent molecules collide more frequently with the solute, and therefore, dissolve it faster.
3. Agitation or stirring increases the rate of dissolving by allowing the unsaturated portions of the solution to come in contact with the solute.

When a solute crystal is placed in a solvent, the dissolving process begins, but shortly after, a dynamic equilibrium is established between the dissolving process and the re-crystallization process. The two processes occur at the same
rate, and therefore, there will be no more net dissolving
happening.

At equilibrium: Rate dissolving = Rate of re-crystallization

Question 4

Factors affecting solubility

Answer 4

1. Temperature - For most solid solutes, solubility increases with heat. Heating increases the spaces between the solvent molecules to allow for more solutes to dissolve.

To increase the solubility of gasses in liquids, the temperature must be dropped. The drop in temperature decreases the speed of motion of the gas molecules and therefore, prevents the gas molecules from escaping the liquid.

2. Pressure - Increasing pressure increases the solubility of gases in liquids, but since solids and liquids are not compressible, we cannot change the pressure in order to change solubility of solids and liquids.
3. Molecule size - Smaller molecules are more soluble than the larger ones.
4. Polarity - Polar solutes dissolve better in polar solvents. Non-polar solutes dissolve better in non-polar solvents (“like dissolves like”).
5. Ionic size and ionic charge - For ionic compounds, in general solubility increase as the ionic size increases, and it decreases as the ionic charge increases.

Question 5

Solution

Answer 5

• a homogeneous mixture of two or more
    substances

 - uniform throughout

Question 6

Solvent

Answer 6

is any substance that has another substance dissolved in it. (usually in the largest amount)

Question 7

Solute

Answer 7

substance dissolved in the solvent

Question 8

Solutions

Answer 8

unlike pure substances can have variable compositions, therefore different ratios of solvent to solute

Question 9

Aqueous solutions

Answer 9

water is the solvent

Question 10

Miscible liquids

Answer 10

can be combined in any proportion, they are readily dissolvable. i.e. Any amount of water dissolves in any amount of ethanol and any amount of ethanol dissolves in any amount of water.

Question 11

Immiscible liquids

Answer 11

liquids that do not readily dissolve.

Question 12

Saturated solutions

Answer 12

formed when no more solute will dissolve and excess solute is present.

Question 13

Unsaturated solutions

Answer 13

solutions that are not yet saturated, more solute can dissolve