CHEMISTRY CHAPTER 13
"Solutions"
A solution is a homogeneous mixture of two or more substances
Ex: Sugar water
The dissolving medium is called a solvent
The substance dissolved is called a solute
Ex: In a solution of Sugar water, water is the solvent sugar is the solute
The solute is said to be soluble in the solvent.
Ex: Sugar is soluble in water
Soluble ionic substances form aqueous solutions which conduct electric current. These substances are called electrolytes
Soluble covalent substances form molecular solutions which do not conduct electric current. These substances are called non-electrolytes
13-2
Not all solutions are composed of a solid into a liquid
Types of Solution
Solute Solvent Example
gas gas air
helium-oxygen [deep sea divers gas]
gas liquid soda water
[carbon dioxide-water]
gas solid hydrogen on platinum
hydrogen-palladium [gas stove lighter]
liquid gas water vapor in air
water-air [humidity]
liquid liquid alcohol in water
water-acetic acid [vinegar]
liquid solid mercury in copper
mercury-silver [dental amalgam
solid gas sulfur vapor in air
naphthalene-air [mothballs]
solid liquid sugar in water
salt-water [sea water]
solid solid copper in nickel
gold-silver [ring]
13-3
Solvents are Selective
This is how a solvent works:
Ex: water & salt [two polar molecules]
Why does oil and water not become a solution?
As a general rule like dissolves like
13-4
A Comparison of Three Major Solvents
Water: H2O
Carbon tetrachloride: CCl4
Ethanol: C2H5OH
13-5
Solution equilibrium is the physical state in which the opposing processes of dissolving and crystallizing of a solute occur at equal rates.
A saturated solution is one that contains the maximum proportion of dissolved solute to solvent under existing equilibrium conditions.
A solution which contains more solute than a saturated solution can hold is said to be supersaturated
Increasing the rate of dissolving
1. By stirring:
Why?
2. By powdering:
Why?
3. By heating the solvent:
Why?
13-6
The Concentration of a solution depends upon the relative proportions of solute to solvent
The more solute dissolved in a solvent the more concentrated the solution becomes
The less solute dissolved in a solvent the more dilute the solution becomes
Ways to express concentrations
Molality (m) is the concentration of a solution expressed in moles of solute per kilogram of solvent
moles of solute
m = ------
kg of solvent
Ex: What is the concentration of a solution containing
1000 ml of water and 1.17 g of salt?
Ex: How many grams of silver nitrate are needed to prepare
a 0.125 m solution in 250. ml of water?
Molarity (M) is the concentration of a solution expressed in moles of solute per liter of solution
moles of solute
M = ------
liters of soln.
Normality (N) is the concentration of a solution expressed in equivalents of solute per liter of solution
equiv.
N = ------
liters of soln.