experimental report

Experiment 3 Determination of saturated vapor pressure of liquid

Experimenter: Shi Yan Tang Feifei Experimental time: 2000.4.19

Temperature: 24.0 ° C atmospheric pressure: 101.7KPa

The purpose is to clarify the definition of pure liquid saturated vapor pressure and the concept of gas-liquid two-phase equilibrium, and to understand the relationship between pure liquid saturated vapor pressure and temperature in the jujube Clausius-Clapeyron equation. The saturated vapor pressure of benzene at different temperatures was measured with an isopipet. Initially master the vacuum experiment technology. Learn to use the graphical method to find the average molar heat of vaporization and normal boiling point of the liquid to be tested in the experimental temperature range.

Instruments and reagents

Vapor pressure tester, rotary vane vacuum pump, precision thermometer, glass thermostatic water bath

a set, benzene

Experimental procedure

Ready to work. Turn on the cooling water. Recognize the role of each cock in the system. Turn on the air intake cock to open the system to the atmosphere. Read the atmospheric pressure p0. Read every half hour later. System leak detection. Turn on the vacuum pump, turn on the suction cock after 2 minutes, close the air intake cock, depressurize the system to a mercury column difference of about 500 mm, and close the suction cock. If the system does not change the mercury column within 5 minutes, the system will not leak. Plug in the power of the heater, controller, and agitator, turn on the agitator, turn on the controller power switch, and adjust the temperature control knob to 52 °C to warm the water bath. After the temperature of the water bath was raised to 52 ° C, the temperature of the water bath was accurately read. Slowly rotate the intake cock so that the bc two liquid level in the balance tube is equal, and read the height of the two mercury columns on the left and right of the U-shaped differential pressure gauge. The saturated vapor pressures of the liquids at 52, 56, 60, 65, 70, 73, and 76 ° C were measured, respectively. The system is ventilated to determine the boiling point of the liquid at atmospheric pressure. After the experiment is completed, disconnect the power supply and water source.

data record

Room temperature: 24.0 °C

Atmospheric pressure p0: 101.7, 101.7 kPa

data processing

P*-t diagram

Lnp*–图

Trend

In the figure above, the yellow line is the trend line of lnp*–curve, which is a straight line whose equation is

Lnp*=?/FONT>128.83+13.132

From the above figure: the slope k = ? / FONT > 128.83

So ΔvHm= –k*R=128.83*8.314=1071J/mol=1.07KJ/mol

When p* is equal to a standard atmospheric pressure, ie p*=101325Pa, the normal boiling point of benzene is

t=128.83/=80.2°C

The literature value of the boiling point of benzene is 80.1 ° C

The atmospheric pressure during the experiment is 101.7Kpa, and the boiling point of benzene is

t=128.83/=80.4°C

The experimentally measured boiling point was 80.50 ° C.

Experimental thinking

First, the pressure and temperature measurements have random errors, try to derive the error transfer expression of ΔvHm.

A: p*=p atmosphere –

Because lnp*=/RT+c

So ΔvHm=RT*

Ln=lnR+lnT+ln

d ln=dlnT+dln

d/ ΔvHm=dT/T+d/

So the error transfer formula is

Δ / ΔvHm = ΔT / T + Δ /

Second, with this device, it is convenient to study various liquids such as benzene, dichloroethylene, carbon tetrachloride, water, n-propanol, acetone and ethanol. Many of these liquids are flammable and should be heated. What is the problem?

Answer: It should be kept away from the fire source. The temperature should not be too high when heating, and the pressure should not be too low when measuring vapor pressure.