Hydrogen bonding between solute and solvent molecules plays an important role.
Substances that give ions when dissolved in water are called electrolytes .
They can be divided into acids , bases , and salts , because they all give ions when dissolved in water.
These solutions conduct electricity due to the mobility of the positive and negative ions, which are called cations and anions respectively..
Strong electrolytes completely ionize when dissolved, and no neutral molecules are formed in solution
Small fractions of weak electrolytes' molecules ionize when dissolve in water. Some neutral molecules are present in their solutions. For example, ammonia, NH4OH, carbonic acid, H2CO3, acetic acid, CH3COOH, and most organic acids and bases are weak electrolytes.
Most solutes have a limited solubility in a given solvent.
When more solute is present than the solubility limit, a dynamic equilibrium is established:
solute + solvent solution
A solution of this type is said to be saturated.
A solution that contains less solute than the solubility limit is unsaturated.
Effects of Temperature on Solubility
Most solids become more soluble as temperature increases. (There are some exceptions.)
If a saturated solution is cooled, with solid present, more solid will precipitate until equilibrium is re-established.
If a saturated solution is cooled with no solid present, sometimes precipitation does not occur immediately. The solution is said to be supersaturated.
Factors affecting solubility
Temperature (more temperature more solubility, in gases is opposite)
Pressure (more pressure more solubility, in gases is opposite).
Size of the solute (the smallest the solute is cut the easy to dissolve)
Nature of solute and solvent (polarity)
The concentration of a solution is the amount of solute dissolved in a certain quantity of solvent.
One measure of concentration is molarity M .
M = (# mol solute)/1 Liter of solution
Tell how to prepare 250 mL of a 3.00 M solution of NaCl. M= # moles / Liters
1. Convert mL to L:
1L -> 1000 mL
x -> 250 mL
2. Convert grams to mol with Molar Mass
Na 23.0 + Cl 35.45 = 58.45 g/mol
58.45 g -> 1 mole
x -> 3 moles ( 3M )
3. Convert grams to volume
175.35 g -> 1 L
x -> 0.250 L|
Preparing solutions of a given molarity
The plan for solving the above problem was:
To actually prepare the solution, 250 mL of 3.00 M NaCl: 1. Transfer 43.8 g of NaCl to a 250 mL volumetric flask partly filled with distilled water. 2. Shake to dissolve. 3. Add enough water to the flask to reach the mark 4. Stopper the flask and invert several times to mix thoroughly . mL L moles grams
Another Molarity Problem
How many mL of 12.00 M HCl solution are required to deliver 0.500 mol?
L = moles/M = (0.500 mol)/(12.00 mol/L)
=0.0417 L 0.0417L x 1000 mL/L = 41.7 mL
Percent by Volume [%(v/v)]
Percent by Volume =
[(volume solute)/(volume solution)]x100%
Calculate the percent by volume alcohol prepared by mixing 15.0 mL with enough water to make a total volume of 50.0 mL.
Percent by volume =
[(15 mL)/(50 mL)] x 100 = 30%(v/v)
50 mL -> 100%
15 mL -> x
Percent by mass [%(w/w)]
Percent by mass
= [(mass solute)/(total mass of solution)]x100%
=[(g solute)/(g solute + g solvent)] x 100%
How many g of NaCl are required to prepare 100 g of a 5.0% solution?
Mass solute = (percent/100)x(total mass)
= (5/100)x100 g = 5.0 g NaCl
x -> 5%
Preparation of Solutions by Dilution
Calculate the volume of 10.0%(v/v) ethanol
require to prepare 500 mL of 5.00% ethanol.
V 1 C 1 = V 2 C 2
Desired [ ]
C 1 = 10.0, V 2 = 500 mL, C 2 = 5.00
V 1 = V 2 C 2 /C 1 = (500mL)(5.00%)/(10.0%)
= 250 mL
Properties of liquids change when solutes are dissolved in them:
boiling point is raised
melting point is decreased
The higher the concentration of solute particles, the greater the effect.
Colligative Properties are properties of solutions that depend on the number of dissolved solute particles.
A solution of 1.00 L of a 1.00 M solution of glucose contains 6.022 x 10 23 particles of glucose molecules.
But a solution of 1.00 L of a 1.00 M solution of NaCl contains 2x6.022x10 23 particles because of ionization.
The freezing point depression of 1.0 M NaCl is almost twice that of 1.0 M glucose.
The temporary dispersion of one substance in another is a mixture called a suspension.
Part of the mixture will settle out from the other part or can be separated by filtration.
Colloids or colloidal dispersions are defined as mixtures having a particle size of 1.0 nm - 100 nm.
Colloids appear milky or cloudy. They scatter light by the Tyndall effect.
There are 8 different types of colloids based on the particles and the phase of the dispersal agent.
Some examples are foams and emulsions.
Colloids are stabilized by emulsifying agents such as soap or bile salts.
Osmosis and Dialysis
Certain materials are:
Permeable: allow water and solvents to pass through.
Impermeable : do not allow solvents to pass.
Semipermeable: material which allows solvent molecules to pass, but not solute molecules.
The process of solute molecules passing through a semipermeable membrane is called osmosis.
If small ions and molecules pass through the membrane with the solvent, but colloidal particles are retained the process is called dialysis .
Insert figure 14.16 A Semipermeable Membrane
The pressure required to prevent the flow of solvent from the less concentrated side to the more concentrated side of a membrane is called the osmotic pressure.
Isotonic solutions is one that has the same osmotic pressure as the fluid in a living cell.
Hypotonic solutions have a lower concentration than inside the cell. Water flows from a solution into a cell.
Osmosis in Cells
The rupture of a cell by hypotonic solutions is called plasmolysis (or hemolysis in the case of red blood cells)
Hypertonic solutions contain a greater concentration of particles than the fluid in cells. Water will flow from the cells to the solution.