CONCENTRATION UNITS

• The term dilute refers to a solution that has a relatively small amount of solute in comparison to the amount of solvent.

• Concentrated, on the other hand, refers to a solution that has a relatively large amount of solute in comparison to the solvent.

MOLARITY

• Molarity (M) is the number of moles of solute per liter of solution.

• M = moles solute/liter solution

ELECTROLYTES AND NONELECTROLYTES

• An electrolyte is a substance that, when dissolved in a solvent or melted, conducts an electrical current. A nonelectrolyte does not conduct a current when dissolved.

• Species such as HCl that completely ionize in water are called strong electrolytes, and those that only partially ionize are called weak electrolytes.

COLLOIDS

• If you watch a glass of muddy water, you will see particles in the water settling out. This is a heterogeneous mixture where the particles are large (in excess of 1,000 nm), and it is called a suspension

• In contrast, dissolving sodium chloride in water results in a tru homogeneous solution,

• A light shone through a true solution is invisible, but a light shone through a colloid is visible because the light reflects off the larger colloid particles. This is called the Tyndall effect.

Colligative Properties

• Some of the properties of solutions depend on the chemical and physical nature of the individual solute.

• colligative properties include:

  • vapor pressure lowering

  • freezing-point depression

  • boiling-point elevation

  • osmotic pressure

Vapor Pressure Lowering

• If a liquid is placed in a sealed container, molecules will evaporate from the surface of the liquid and eventually establish a gas phase over the liquid that is in equilibrium with the liquid phase.

• The pressure generated by this gas is the vapor pressure of the liquid.

• The higher the concentration of solute particles, the less solvent is at the interface and the lower the vapor pressure. This relationship is referred to as Raoult’s law.

Osmotic Pressure

• If you were to place a solution and a pure solvent in the same container but separate them by a semipermeable membrane you would observe that the level of the solvent side would decrease while the solution side would increase.

• This indicates that the solvent molecules are passing through the semipermeable membrane, a process called osmosis.

• The difference in the two levels is related to the osmotic pressure.

• one could exert a pressure on the solution side exceeding the osmotic pressure, and solvent molecules could be forced back through the semipermeable membrane into the solvent side.

• This process is called reverse osmosis and is the basis of the desalination of seawater for drinking purposes.

COMMON MISTAKE

1. In molarity problems, be sure to use liters of solution.

2. Make sure your units cancel, leaving you with the units desired in your final answer.