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

• "Like dissolves like."

• hydrophobic versus hydrophilic
• When ionic solid dissolves in water, ions are surrounded by water.
• Not all ionic compounds are soluble in water. Why?

• Some compounds can be solvated via hydrogen bond.

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 g/100mL
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
PO₄^3–, CO₃^2–, and S^2– 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 75.0 g of a 7.20% w/w aqueous glucose solution?
7.20% w/w glucose solution = 7.20 g glucose/100 g solution
75.0 g solution ´ 7.20 g glucose/100 g solution = 5.40 g glucose
Amount of water needed: 75.0 g – 5.40 g = 69.6 g
Take 5.40 g glucose and disolve it in 69.6 g water.
checking: 5.40/(5.40+69.6)´ 100% = 7.20%

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

example: 75 mL ethanol diluted to a volume of 250 ml by water
(v/v)% = 75 mL/250mL ´ 100% = 30%

          [(75 ´ 0.95)/250] ´ 100% = 28.5%

example: How many mL of alcohol is in a 750-mL bottle of 12.5% wine?
A typical "proportionality" question!
Think this way: In every 100 mL wine, there is 12.5 mL alcohol. How many mL is there in 750 mL?
12.5/100 = V/750 Þ V = 93.8 mL
or, simply think: 12.5% of 750 mL is 750 mL ´ 0.125 = 93.8 mL

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.
250 mL solution ´ 4.8 mL acetone/100 mL solution = 12 mL acetone
amount of water needed: 250 mL – 12 mL = 238 mL

example: How many g NaCl is needed to make 500 mL physiological saline, 0.90% NaCl (m/v)?
500 mL ´ 0.0090 g/mL = 4.5 g (NaCl needed)
Put 4.5 g salt in small amount of water until it is completely dissolved.
Then, add water to a volume of 500 mL.

Molarity is the most important concentration unit in chemistry!

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

Examples:
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?

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

Examples:
1) How much solvent is needed to dilute 100 mL of a 0.090 M solution into 0.0015 M?

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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).

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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(n/V)RT

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