Bedienungsanleitung Casio EA200 (Seite 34 von 55) (Englisch)

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Activity: SetupActivity: Setup

2-11-1

í Equipment

Stand Heater Reflux Condenser Desiccant

Auto Stirrer Beaker Round Bottom Flask (2) Mixing Stick

Ice Water Benzene Naphthalene

Temperature Measurement Setup (EA-200, graphic scientific calculator, data

communication cable, temperature probe)

í Setting Up the Boiling Point Elevation Equipment

u Pour the benzene solution into the flask, and secure it in place as shown in the illustration.

This activity investigates boiling point elevation and freezing point depression of a dilute

solution.

Dissolving a small amount of a substance (solute) in a theoretically pure liquid (solvent) to

create a dilute solution causes the boiling point of the dilute solution to become greater than

and the freezing point to become less than that of the solvent. This is because the

proportion of solvent molecules is reduced by the amount of solute molecules mixed in,

which lowers the vapor pressure of the solvent and elevates the boiling point. At the same

time, it also reduces the proportion of solvent molecules that congeal, which suppresses the

freezing point. These changes are determined by the amount of solute molecules, and the

type of solute does not matter, as long as it is non-volatile. Consequently, both boiling point

elevation and freezing point depression are proportional to the solute molality, as shown in

the expressions below.

(°C) : Boiling Point Elevation of Solution

(°C) : Freezing Point Depression of Solution

(°C kg/mol) : Molal Boiling Point Elevation Constant

(°C kg/mol) : Molal Freezing Point Depression

Constant

m(mol/kg) : Molality

Here, the proportion coefficient is determined by the solvent type. It is a constant that is not

affected by the solute type. For example, the molal boiling point elevation constant for benzene

is 2.53°C kg/mol, and the boiling point is 80.1° C. The molal freezing point depression constant

is 5.12°C kg/mol, and the freezing point is 5.53° C.

Dilute Solution Properties

Theory

When the solvent is pure water, the molal boiling point elevation constant is 0.515°C kg/mol,

and the boiling point is 100°C. The molal freezing point depression constant is 1.853°C kg/mol,

and the freezing point is 0°C.

í Setting Up the Freezing Point Depression Equipment

u Pour the benzene solution into the flask, and secure it in place as shown in the illustration.

1 Stand

2 Heater

3 Round Bottom Flask

4 Reflux Condenser

5 Desiccant

6 Naphthalene-Benzene

Solution

7 Te mperature Probe (CH1)

8 EA-200

9 Water Flow Direction

1 Stand

2 Auto Stirrer

3 Beaker

4 Round Bottom Flask

5 Mixing Stick

6 Ice Water

7 Te mperature Probe (CH1)

8 EA-200

1 Solvent

2 Solution

3 Boiling Point Elevation

4 Freezing Point Depression

T(°C) : Temperature

P(atm) : Vapor Pressure

t(s) : Time

ͬT

= K

ͬT

= K

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