Chapter 21
Solutions
1. How Solutions Form
a. What is a Solution?
b. Solution-A homogeneous mixture; mixture that appears the same throughout
c. Solutes and Solvents
i. Solute - substance being dissolved.
ii. Solvent- substance doing the dissolving.
iii. Example: in saltwater, salt is the solute and water is the solvent
iv. Solutions can be solids liquids or gases.
v. Non liquid solutions-Alloys are metal solutions; air is a gas solution
d. How substances dissolve :
i. Water molecules are polar - they have a positive area and a negative area.
ii. Water molecules cluster around solid molecules, with their negative ends
attracted to the positive ends of the solids.
iii. Water molecules pull the solid particles into solution.
iv. The moving water molecules and solid molecules spread out and evenly mix to
form a solution.
v. To mix solids to make an alloy, you must melt the solids.
e. Rate of dissolving depends on:
i. Stirring- speeds up dissolving by bringing more fresh solvent into contact with
more solute.
ii. Surface area- increase by breaking a solid solute into smaller pieces (crushing)
iii. Temperature-speed up rate of dissolving by increasing the temperature of a
solvent which speeds up the movement of its particles
iv. To make a gas dissolve more quickly in a liquid cool the liquid solvent and
increase the pressure of the gas.
2. Concentration and Solubility
a. Concentration
i. A concentrated solution has a large amount of solute in the solvent.
ii. A dilute solution has a small amount of solute in the solvent.
iii. The concentration of a solution is the amount of solute actually dissolved in a
given amount of solvent
b. Solubility - the amount of a substance that can dissolve in solvent.
i. Depends on the nature of substances
ii. If the solute does not dissolve completely, then the solute falls to the bottom of
the container
iii. Solubility of two substances can be compared by measuring
c. Types of solutions
i. Saturated solution- contains all the solute it can hold at a given temperature.
1. As the temperature of a liquid increases the amount of solute that can
dissolve in it increases.
2. Solubility curve - line on the graph used to figure how much solute can
dissolve at any temperature on the graph
ii. Unsaturated solution - able to dissolve more at a given temperature.
iii. Supersaturated - contains more solute than a saturated one at the same
temperature.
3. Particles in Solution
a. Ions- particles with a charge
i.
Electrolytes - compounds that form charged particles (ions) and conduct electricity in
water.
ii.
Non-electrolytes - substances that do not ionize in water and cannot conduct
electricity.
b. Ion Formation in Solution
i.
Ionization- molecules break apart in water, causing atoms to become ions by taking
on a charge.
ii.
Dissociation- an ionic solid separates into positive and negative ions.
c. Effects of Solute Particles
i.
All solute particles- polar, nonpolar, electrolyte, and non-electrolyte - effect the
physical properties of the solvent
ii.
Adding a solute to a solvent lowers the freezing point because the added solute
particles interfere with the formation of the orderly freezing pattern.
iii.
Adding a solute raises the boiling point because fewer solvent molecules can reach
the surface and evaporate.
4. Dissolving without water
a. Nonpolar materials have no positive or negative areas.
i.
They are not attracted to the polar water molecules so they do not dissolve easily
into water.
ii.
Examples: oils contain hydrocarbons (Large molecules of carbon and hydrogen
atoms).
iii.
These atoms share electrons in an equal manner so that there is no positive or
negative charge.
b. Useful nonpolar molecules
i.
Nonpolar solvents dissolve nonpolar solutes.
ii.
Many nonpolar solvents are toxic (dangerous to touch or inhale).
iii.
Soap is used for washing because it has polar and nonpolar properties.
c. Polarity and Vitamins
i.
B vitamins and Vitamin C are polar (dissolve in water in your body cells).
ii.
Vitamin A is a nonpolar (dissolves in the fat of some body cells).
Chapter 21 Vocabulary
Alloy - A mixture of elements that has metallic properties
Concentration - The amount of solute actually dissolved in a given amount of solvent
Dissociation - Process in which an ionic compound separates into its positive and negative ions in
solution
Electrolyte - Compound that breaks apart in water, producing charged particles (ions) that can conduct
electricity
Ionization - Process in which electrolytes dissolve in water and separate into charged particles
Nonelectrolyte - Substance that does not ionize in water and cannot conduct electricity
Saturated solution - Any solution that contains all the solute it can hold at a given temperature
Solubility - Maximum amount of a solute that can be dissolved in a given amount of solvent at a given
temperature
Solute - In a solution, the substance being dissolved
Solvent - In a solution, the substance in which the solute is dissolved
Supersaturated solution - Any solution that contains more solute than a saturated solution at the same
temperature
Unsaturated solution - Any solution that can dissolve more solute at a given temperature