A short guide to chapter 9, the chemistry
of solutions
Some definitions first:
solution-a homogeneous mixture of two or more substances.
solute-the dissolved substance or the least abundant component in the solution.
solvent-the dissolving agent or the most abundant component in the solution.
solubility-the maximum amount of solute that will dissolve in a specified amount of
solvent under stated conditions (temperature), in units of grams of solute per 100 grams
of solvent, usually water.
miscible-capable of mixing to form a solution, generally liquid solute and liquid solvent
Properties of solutions:
1) homogeneous mixture
2) variable composition (concentration)
3) solute is molecular or ionic in size
4) transparent
5) uniform distribution of solute-no settling over time
6) solute separated by physical means; example, evaporation
What affects solubility?
1) Nature of solvent and solute (like dissolves like), intermolecular forces, compare salt
and water vs. oil and water vs. ethanol and water
2) Temperature (energy)-Have you ever made rock candy (sugar crystals)?
3) Partial Pressure (greatest effect shown with dissolved gases)-Where’s the fizz come
from in soda pop?
What affects the rate of dissolution?
1) Particle size (the smaller, the faster)
2) Temperature
3) Concentration (unsaturated, saturated, supersaturated)
4) Agitation (kinetic effect)
Units for Solutions:
Weight % (w/w)
= (grams of solute / grams of solute + grams of solvent) * 100
= (grams of solute / grams of solution) * 100
Weight/Volume % (w/v)
= (grams of solute / milliliters of solution) * 100
Volume % (v/v)
= (volume of liquid solute / volume of solution) * 100
Molarity (M, mol/L)
= moles of solute / liters of solution
Parts per million (ppm)
= (part / total parts) * 106
the unit for the part and the total parts must be the same, so
ppm by mass = [mass of solute (g) / mass of solution (g)] * 106
ppm by volume = [volume of solute (mL) / volume of solution (mL)] * 106
A great test of your conversion skills is to determine the
weight %
ppm by mass
molarity
for a 75.0% (w/v) NaCl solution whose density is 1.21 g per mL of solution.
Dilution:
M1V1 = M2V2
What does this mean?
Moles of solute at beginning of dilution = Moles of solute at end of
dilution
Electrolyte- any substance that dissolves in water to give a solution
that conducts electricity
Equivalent (of an ion) = Molar Mass of Ion (g) / Number of Charges on Ion
one equivalent of Li+ = 6.941 g / 1 = 6.941 g
one equivalent of Cr3+ = 52.00 g / 3 = 17.33 g
Normality (N, eq/L) = equivalents of solute / liters of solution
Analytical laboratories often use normality. I’ll give you some examples to understand it
but I will not focus on it.
So first, what is an equivalent? Rather than give a definition, I’ll demonstrate it and you
can come up with your own definition.
You have 1.0 L of a 1.0 M HCl solution and 1.0 L of a 1.0 M H2SO4 solution.
If NaOH is used to neutralize each acid separately how many moles of H+ were
consumed?
1.0 M * 1.0 L = 1.0 mol HCl = 1.0 mol H+
1.0 M * 1.0 L = 1.0 mol H2SO4. = 2.0 mol H+
How many equivalents (of H+) were consumed for each mole of acid?
1.0 mol HCl = 1.0 mol H+ = 1.0 equivalent
1.0 mol H2SO4. = 2.0 mol H+ = 2.0 equivalents
What is the normality of each original acid solution?
HCl: 1.0 eq / 1.0 L = 1.0 N
H2SO4 2.0 eq / 1.0 L = 2.0 N