Solutions
Dec 21, 2015
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?
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