Chem Lab Colligative Properties: Freezing Point Depression And Molar Mass Midterm

Front 1

Purpose

Back 1

to find the molar mass of an unknown and become familiar with colligative properties

Front 2

Method

Back 2

Part a

-measure cyclohexane, pour in test tube and place in an ice/salt/water bath, gently stir until crystals form

-remove from bath and measure temp every 30 sec until we reach a temp between 12 to 15c.

-plot data on graph and use inflection point to determine the freezing point

Part b

-weight the unknown and add to cyclohexane

-place in ice/salt/water bath and gently stir with metal rod until slush appears

-remove from bath and record temp every 30 seconds until a temp between 10 to 15c is reached

-plot data on graph and determine the freezing point

-use this information to determine the molar mas of the unknown substance

Front 3

what are solutions?

Back 3

homogeneous mixtures that contain two or more substances

Front 4

what are solvents?

Back 4

the major component solution

Front 5

what are solutes?

Back 5

the minor component in a solution

Front 6

what are colligative properties?

Back 6

they are independent of the nature of the solute, depend only on the concentration

Front 7

what are four colligative properties?

Back 7

1.vapor pressure lowering

2. boiling point elevation

3. freezing point depression

4. osmotic pressure

Front 8

what happens when vapor pressure = atmospheric pressure?

Back 8

the solvent boils at this temperature and the gaseous and liquid states are in dynamic equilibrium

Front 9

what have experiments found about the dissolution of non-volatile solutes in a solvent?

Back 9

it lowers the vapor pressure of solvent, raises the boiling point, and lowers the freezing point

Front 10

what does anti-freeze do concerning colligative properties?

Back 10

lowers the freezing point and raises the boiling point of coolant (water)

Front 11

what is salt used for concerning colligative properties?

Back 11

melts ice

Front 12

what is the colligative property law?

Back 12

states that the freezing point and boiling point of a solution differ from those of the pure solvent by amounts that are directly proportional to them molal concentration of the solute

Front 13

what is the formula of the relationship for freezing point lowering and boiling point elevation?

Back 13

^T = Km

^T is the change in temperature

K is the constant

m is molality of solution

Front 14

what is supercooling?

Back 14

the lowering of temperature of a substance below the normal freezing point without making the substance into a solid, cooling slowly while rapidly stirring

Front 15

what is another name for temp/time graphs?

Back 15

cooling curves

Front 16

list the colligative properties and suggest a ratinoale for the choice of the word colligative to describe the properties.

Back 16

1. vapor pressure lowering

2. freezing point depression

3. boiling point elevation

4. osmotic pressure

they are colligative because they are dependent on the concentration of the solute, not the identity

Front 17

distinguish between volatile and non-volatile

Back 17

volatile, high vapor pressure at room temperature (easily evaporates)

non-volatile, low vapor pressure at room temperature (do not evaporate easily)

Front 18

what effect does the presence of a non-volatile solute have upon the vapor pressure?

Back 18

lowers vapor pressure

Front 19

what effect does the presence of a non-volatile solute have upon the freezing point?

Back 19

lowers the freezing point

Front 20

what effect does the presence of a non-volatile solute have upon the boiling point?

Back 20

raises the boiling point

Front 21

what do colligative properties depend on?

Back 21

number of particles present (concentration of solute)

Front 22

what do colligative properties not depend on?

Back 22

type of particles (solute)