Solutions

Some definitions….

Solution: homogeneous mixture of at least two substances where each retains its own chemical identity

Solvent: the component of a solution that is in greatest amount

Solute: the component(s) of a solution that is/are less abundant than the solvent

Solubility

The maximum amount of solute that will dissolve in a given amount of solvent under a given set of conditions

How do the following factors influence solubility?

Temperature (solid in a liquid) (gas in a liquid)

Pressure (gas in a liquid)

Amount of solute present

Saturation

Saturated: solution has the maximum amount of solute dissolved under the conditions it is at

Unsaturated: solution has less than the maximum amount of solute that can be dissolved under the conditions it is at

Supersaturated: unstable solution that has more solute than can normally be held under the given conditions

Dissolving and Saturation

At saturation, the dissolving process does not stop. Rather it reaches a dynamic equilibrium (solute enters and leaves the solution at the same rate)

Concentrated vs Dilute

Concentrated vs dilute:

depends on the amount of solute present compared to how much is capable of dissolving

Aqueous solutions and the dissolving process

Aqueous solutions: solutions in which water is the solvent i.e. NaCl(aq)

Hydration: water molecules interrupt attractions within the solute and surround the solute components bringing them into solution

Ionic compounds “dissociate” into ions while covalent compounds stay intact

Dissolving Process

Rule of thumb: “likes dissolve likes”Polar solvents typically dissolve:Polar solutes or ionic solutes

What types of interactions are occurring?

Solubility “Rules”

Using solubility rules to predict precipitation reactions

Write the compounds present on the reactant side

Dissociate them into ions

Ask if the cation of one will precipitate (form an insoluble solid) with the anion of the other

If so: it is a solid product If not: spectator ions

Write the net equation

Units of concentration

Percent by mass: g solute / 100 g solution

Percent by volume: mL solute / 100 mL solution

Mass-volume percent: g solute / 100 mL solution

Molarity: (M) moles solute / liter solution

Calculations

Concentration x volume = solute amount

Re-write % as g / 100 mL

Re-write M as moles / L

Try some

Dilution calculations

C1 V1 = C2 V2

C can be molar or percent but must be the same on both sides

Volume can be any unit but must be the same on both sides

Try some

Colligative properties

Properties of solutions that depend on the concentration of dissolved solute particles present but not its identity

Hypertonic Hypotonic Isotonic Osmosis Dialysis

More Colligative Properties

Boiling point elevation

Freezing point depression

Electrolytes

Solutes that when dissolved, conduct electricity

Must ionize

Examples: ionic compounds, acids and bases