Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: daixieit

Chemistry1 CHEM10003

Experiment 2: The Preparation of Paracetamol

2022

Experiment 4: Vapour Pressure of a Volatile Liquid

Name:

Day/Time/Group number: (class you attended)

Aims:

• To observe the changes in equilibrium vapour pressure of a volatile liquid with temperature, from vacuum line measurements

• To determine a value of the latent heat of vapourisation of a liquid.

Experimental:

Refer to Student Notes Experiment 4 University of Melbourne 2022

Results:(Tables of data)

PART A: MANOMETER PRESSURE MEASUREMENT

Manometer pressure reading, prior to start of experiment: 1 m bar______________   

PART B:  TABLE 1 VAPOUR PRESSURE MEASUREMENTS

Liquid Sample: Name n-pentane    Formula C5H12

Manometer pressure reading, after experiment: 1 m bar______________   

Part C: TREATMENT OF DATA

TABLE 2: Equilibrium vapour pressures of n-pentane at different temperatures.

Experimental data sets measured at different T (°C):     Data for graph:

Graphing data – use Excel or plot by hand and paste below

Plot ln p (y-axis) versus 1/T (x-axis).

If using Excel

Equation of the line:_________________________________________________________

R ² value:__________________________________________________________________

Excel Graph: Use this data in Q2, Q3 and Q4 below

Questions:

REMEMBER THAT ANSWERS NEED TO BE SUPPORTED BY EVIDENCE FROM YOUR DATA OR THEORY

Question 1
Consider the diagram of the vacuum line below; the line is under vacuum and the manometer has a pressure reading of 1 mbar.  The system has developed a leak at one of the connections.  What do you expect to happen to the pressure reading over the next ten minutes and why?

If the system has developed a leak at one of the connections. Propane will begin to melt into liquid. Because the leak will continuously enter the air into the pump. The pressure will begin to rise until the pressure in the pump and the atmospheric pressure balance. As the pressure in the pump rises, the liquid nitrogen begins to boil. So propane will begin to melt into a liquid.

Question2

Using the equation of the regression line from your Excel plot, what is the gradient of the line of best fit (show units)? Or if hand plotted, show working and determine gradient of the line:

Question 3

Calculate the heat of vapourisation (ΔH_vap) of n-pentane from the gradient of your graph according to equation 4.2 (include units). Show all working.

Question 4

Using the value of ΔH_vap obtained from your graph and a pressure-temperature data pair                 (lnp₁ , 1/T₁) from the graph, calculate the normal boiling point of n-pentane using equation 4.3. Show all working.

[HINT: The normal boiling point (T₂) will be at the atmospheric pressure, ρ₂ = 1013 mbar. The universal gas constant R is 8.314 JK⁻¹mol⁻¹].

Data pair from line of best fit: lnρ₁ value_______________ 1/T₁ value_________________

Question 5

Complete Table 3 below, comparing the properties of water and pentane, adding your values determined from the experiment and the Prelab. Question regarding safety advice for use of pentane (with bibliographic reference):

Table 3 Comparison of properties of water and pentane

Reference for safety data:

…………………………………………………………………………………………………………………………………………..

In the polymer industry, pentane is added to preformed granules of polymer.  The mixture is heated to the boiling point of pentane, which vapourises and expands in volume leaving tiny voids/empty pockets in the structure of the polymer (pentane is called a ‘blowing agent’).  This makes a light, low density product.

In the production of the polymer, pentane or water could be used as a blowing agent.

Identify one advantage and one disadvantage in using pentane rather than water with a brief explanation.

(Are there any environmental/energy/safety concerns, based on the data in Table 3?

Note: There are environmental concerns associated with waste and decomposition of polymers but this question refers to the manufacture of polymers.)

Advantage:

Disadvantage:

Conclusion:

(What have you found out?)