03. Colligative Properties

Which of the following is not a colligative property?
a. vapor pressure

b. density
c. osmotic pressure

d. boiling point

b. density

When 23.0 grams of sodium chloride is dissolved in 100.0 grams of water,
how many moles of ions are in the solution?

NaCl=58..44 g/mol

23.9/58.44 =0.394 × 2 ions

=0.788 moles of ions

Explain the effect on the concentration of the solution if it is “over-
boiled”

Over boiling increases the rate of water vaporization, and in return, increases the solute concentration. This is because more water is leaving the solution and leaving solute behind

How would the boiling point of a pure sample of water compare to the
boiling point of a solution made from ethylene glycol and water?

Pure water boils at 100C. Ethylene glycol dissolves in water, breaks into molecules, and in return increases boiling point since there are ore particles in the water

Lab Purpose:

To observe the effect of a dissolved substance on the physical properties of solutions and to be able to calculate the molar mass of the nonvolatile solute
from the experimental data

Colligative Properties are

the properties of solutions that are affected by the presence of dissolved particles
(solutes).

The colligative properties are

vapor pressure, freezing point, boiling point, and osmotic pressure

The effects of colligative properties are due to

the physical presence of the solute, not to the type of solute present.

Effects on vapor pressure:

A solute particle gets in the way of solvent particles leaving the solution and thus lowers the vapor pressure of the solution. It would require a higher temperature to obtain the same vapor pressure of a solution as the pure solvent

Effects on boilliing Point (remember….)

-Since more energy is required to cause the same vapor pressure, the temperature at which a substance boils would be higher.

(Remember boiling occurs when the vapor pressure equals atmospheric pressure)

Effects on Freezing Point

Since the solute particles are physically in the way, more energy needs to be removed from the solution in order to organize the solvent particles into the solid
formation. Thus, the freezing point is lowered.

Effect on Osmotic Pressure

There is an overall net gain of solvent into the side that is more concentrated since only solvent molecules can pass through the semi-permeable membrane. With a larger difference between the two sides, there is a bigger osmotic pressure.

equation for molality

moles solute / kg H2O

Equation to find molality

Delta Tb= ikbm