Solution: A homogenious mixture of one matter (solute) in another matter (solvent). Solute and solvent can be either liquid, solid, or gas., e.g., air (O2/N2), dental amalgam (Ag/Hg), alloy (e.g., Zn/Cu)
Solvation: (Secondary) interaction between solute and solvent Aqueous solutions: Forming solutions with water as the solvent
Hydration: solvation by water
Ionic compounds in water
Water as an integral part of the crystal structure;
e.g., water in CuSO4•5H2O (Six H2O’s are surrounding the Cu2+.)
Water molecules in protein crystal structures (What's the significance of this?)
The water can be removed to give dehydrated form
e.g., heating CuSO4•5H2O
Solubility—the maximum amount of solute dissolves in a unit volume of a solvent at a given temperature (to produce a saturated solution).
Soluble salts Insoluble salts
BaCl2 35.7 g/100mL
BaSO4 2.4 ´ 10–4
FeSO4 26.5 CaF2 1.6 ´ 10–4
BaI2 203.1 FeS 6.2 ´ 10–4
HgCl2 6.1 Hg2Cl2 2.0 ´ 10–4
Solubility rules: (Table 7.3)
Na+, K+, NH4+, NO3–, acetate, salts are soluble
PO43–, CO32–, and S2– salts are insoluble, except with above cations.
Factors affecting solubility
• Temperature—In general, solubility becomes higher (to different extents) for solid compounds at higher temperature.
—Gases become less soluble at higher temperature
• Pressure—Henry's law (Chapter 5): At a given temperature, the solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid (e.g., Soda can and the bends), i.e., S1/P1 = S2/P2
• Supersaturation—of solids? of gases? What’s going to happen when disturbed?
Concentration—a measure of the amount of solute dissolved in a given quantity of the solution or solvent
i.e., concentration = amount of solute (mass, volume, or moles)/unit
of solution or solvent (mass or volume)
Name/define different units of concentration you know.
Percent concentration (composition)
(using mass units or/and volume units)
(A) mass percent concentration
(w/w)% = (mass of solute/mass of solution) ´ 100%
example: How to prepare 200 g of a 5.50% w/w aqueous glucose solution?
200 ´ 5.50/100 = 11.0 g glucose needed
amount of water needed: 200 g – 11.0 g = 189 g
[(75 ´ 0.95)/250] ´ 100% = 28.5%
example: How is an aqueous 4.8% v/v acetone solution prepared?
4.8% v/v = 4.8 mL acetone/100 mL solution
For the preparation of 100 mL solution, amount of water needed:
100 mL – 4.8 mL = 95.2 mL
Prepare 250 mL of above solution.
mL solution ´
4.8 mL acetone/100 mL solution = 12 mL acetone
amount of water needed: 250 mL – 12 mL = 238 mL
Molarity is the most important concentration unit in chemistry as it is based on mole!
e.g., 9.0 g glucose in 500 mL (0.5 L) water gives a solution of
(9.0/180)/0.5 = 0.1 M
ppm and ppb: parts per million and parts per billion
—useful for trace pollutants and toxic substances
1 ppm = 1g solute/106 g solution, i.e., 1 mg per kg
= 1 mg solute/1 kg solution (~1 mg/1 L water)
Thus, 0.50 mg of Pb(II) in 2.0 L of polluted water is
0.50 mg/2.0 L = 0.25 ppm
1 ppb = 1 g solute/109 g solution
= 1 m g solute/1 kg solution (1 L aqueous solution)
Thus the above solution is
500 m g/2.0 L = 250 ppb
1) What is the mass-mass percent concentration of a 5.0% (m/v) NaCl solution? Assuming the addition of small amount of salt into water does not change the volume of the water.
5.0% (m/m) = 5.0 g solute/100 g solution
In this 100 g solution, there is 5.0 g salt and 95 g (= 95 mL) water.
Thus, (m/v)% = 5.0 g salt/95 mL = 5.3%
3) What is the molarity of the 5.0% (m/v) NaCl solution?
5.0% (m/v) NaCl = 5.0 g NaCl/0.1 L solution
= (5.0/58.5)/0.1 = 0.85 M
4) What is the 5.0% (m/m) NaCl solution in molarity?
Dilution of solutions
1) Number of moles before dilution = number of moles after dilution
M1 (mol/L) ´ V1 (L) = M2 (mol/L) ´ V2 (L)
2) Amount in mass before dilution = amount in mass after dilution
1) How much solvent is needed to dilute 100 mL of a 0.090 M solution into 0.0015 M?
The following are important properties associated
with concentration that are not mentioned in the textbook!!
Collegative properties: Solution properties that depend on the number of particles dissolved in a given mass of solvent
Vapor pressure lowering—solution with nonvolatile solute has lower vapor pressure than pure solvent (thus, higher temperature is needed to raise the vapor pressure the same as pure solvent, e.g., adding salt into water)
Boiling point elevation—Because of the lowering of the vapor pressure of solvent with nonvolatile solute.
Freezing point depression—Such as the addition of salt to water can prevent water from freezing at 0 °C (also, spreading salt on highway to "melt" ice).
Solubility and Chemical reactions
Insolubility can result in chemical reactions in solutions:
Osmosis and dialysis: The flow of water through a semipermeable
membrane (from lower to higher concentrations).
examples: Swimming in the sea for a while, your skin may become wrinkled because water flows "out of your body" into the salt water.
A red blood cell will burst open when it is put in pure water, because water flows into the cell.
"Osmolarity": The "concentration" equivalent of molarity in osmosis
P = i(nRT/V)
Do you notice that the equation is familiar to you? Sure, the ideal gas law P = nRT/V.
P is the osmotic pressure in atm
R is the gas constant
T is the temperature in K
V is the volume in L
n is the number of moles (thus, n/V is the molar concentration)
i is a factor that correct the number of particles per mole of solute. Thus, it is 1 for glucose, 2 for NaCl (dissociates into Na+ and Cl–), 3 for CaCl2, and 4 for soluble MCl3, and so on.
Ultrafiltration: water and small molecules are forced to go through a semipermeable membrane by hydrostatic pressure, such as "squeezing" water out of protein solution in the kidneys.
isotonic: outer solution has the same concentration as the internal solution of a cell; thus there is no flow of water across the cell membrane
hypotonic: outer solution has lower concentration than the internal solution of a cell; thus there is a net flow of water into the cell, e.g., hemolysis of red blood cells
hypertonic: outer solution has higher concentration than the internal solution of a cell; thus there is a net flow of water out of the cell, causing contraction of the cell.
Other terms: colloids, micelles, CMC, and diffusion