Soln notes

solutions (solns)
Solutions (Soln): Solutions are homogeneous mixtures. They are not pure substances.
They can be solids (alloys), liquids, or gases.
True solns consist of two parts, the solute and solvent.
Solute: the part that is dissolved
Solvent: the part that does the dissolving, usually, but not always a liquid.
Carbonated water: CO2 (gas) is the solute, water is the solvent
Saline solution: Salt (solid) is the solute, water is the solvent
Tincture of iodine: Iodine (solid) is the solute, alchohol is the solvent.
When both the solute/solvent are in the same phase, (both liquids, or both gases etc)
the one with the greater amount is the solvent.
Example: Brass is a homogeneous solid solution (alloy) consisting of 5
grams of solid Zinc and 95 grams of copper. The copper is the solvent and the zinc is
the solute.
“Like dissolves like”
This phrase refers to the fact that nonpolar solvents will dissolve nonpolar substances,
and polar solvents will dissolve polar substances as well as most ionic substance. The
term polar and nonpolar only refers to covalently bonded substances. The nature of the
molecule determines whether a particular solvent will be able to dissolve it or not.
Dissolving a solid in a solvent is a physical change. By evaporating the solvent, the
solid can be recovered. The fact that you no longer see the solid, does not mean it is
not present in the solution.
The amount of solute that will dissolves is temperature dependent. The majority of
solids will have greater solubility at higher temperature (more will dissolve).
Gases on the other hand dissolve less at higher temperatures. So increasing the
temperature will cause the solubility of a gas to decrease. The solubility of a gas is also
pressure dependent. Increasing the pressure will increase the solubility of a gas in a
solvent. Pressure does not affect the solubility of liquids or solids.
Be able to read a solubility graph.
When ionic substances dissolve they disassociate (break apart) into their ions. These
ions will conduct an electric current. Any solute, that when dissolved in water, conducts
an electric current is called an electrolyte. Only ionic substances can be electrolytes
because they are the only ones that can produce ions.
Categories of electrolytes: acids/bases/ionic solids
When covalent substances dissolve they do not dissassociate. The atoms remain
attached to each other as they share their outer valence electrons. No ions are formed
and this type of solution cannot conduct an electric current. These substances, when
dissolved are called nonelectrolytes.
Saturation occurs when the solute can no longer dissolve. The solvent is holding as
much dissolved solute as it can. It does not mean that the solute has stopped
dissolving though. The solute continues to dissolve, but for every molecule that
dissolves, another one is “undissolving” or turning back into its solid form.
Unsaturated solns are ones in which the solvent has the ability to dissolve some more
The solubility of one cpd is not affected by the solubility of another, unless they have a
common ion.
Example: What is the solubility of sodium chloride at 25 C?
What is the solubility of potassium nitrate at this same
Concentration is measured in moles/liter and is called Molarity (M)
Molarity is sometime called Molar.
Molarity = moles solute
Liter of soln
6 mole dissolved in enough water to make 3 Liter has a concentratio of:
6 mole = 2 Molar or 2 M
12 moles solute dissolved in enough water to make 24 Liter has a concentration of:
12 mol = 0.50 Molar or 0.50 M
24 L
The volume MUST be in liters. If volume is given in milliliters you must convert.
3.0 Moles dissolved in 200. mls has a concentration of :
3.0 Moles = 15 Molar or 15M
0.2oo L
If the amount of solute is given in grams, molecules, or liters at STP you must first
convert to moles before calculating the volume.
Since M = mole
M x V(liters) = moles
If you have 3 liters of a 5 Molar soln how many moles of solute are present?
5 M x 3 L = 15 moles
If you have 2 Liters of a 1.5 Molar soln of NaOH how many moles of NaOH do you
1.5 Molar x 2 Liters = 3.0 Moles NaOH
How many grams of NaOH was dissolved?
3.0 Moles NaOH x 40 grams/mole = 120 grams of NaOH
When you dilute something, you lower its concentration by adding more solvent note
solute. Therefore the amt (moles) of solute remains the same
moles solute1 = moles solute 2
M1V1 = M2V2
3 Liters of a 2 Molar soln of KCL are diluted with 6 Liters of water. What is the new
(diluted) concentration of the soln?
2 M x 3 L = M2 x 9 L
6 Moles = M2 x 9L
6 mole/9 L = M2
0.67 Molar KCl = M2
400. mls of a 3.0 Molar soln of NaOH are diluted with 200 mls of water. What is the
new concentration?
3 M x 400 mls = M2 x 600 mls
1200 millimoles = M2 x 600 mls
1200 millimoles = M2
600 milliliters
2 Molar NaOH = M2