Colligative properties (Maria M, Kristina P, Victor S and Alvaro Puig)

Colligative properties

Solutions have different properties than either the solutes or the solvent used to make a solution. Those properties can be divided into two main groups: colligative and non-colligative properties. Colligative properties depends only on the number of dissolved particles in solution and not on their identity. Non-colligative properties depend on the identity of the dissolved species and the solvent. 

- Vapor pressure and Raoult's Law

Raoult's law states that the vapor pressure of an ideal solution is dependent on the vapor pressure of each chemical component and the mole fraction of the component in the solution. 

So the addition of a nonvolatile solute to a pure solution decreases the vapor pressure of the solution (related to the relative number of solvent molecules tos solute particles). 

If you have a nonvolatile solute in a solution, the vapor pressure of the solution is equal to the vapor pressure of the pure solvent multiplied by the mole fraction of the solvent in the solution. As we can see explained on the next example: 

* Pure Water

The vapor pressure is caused by some molecules turning from liquid to gas, therefore causing vapor pressure.

* Solution of pure water and salt (that wont turn into a gas)

Because there are now salt molecules taking up the space on the surface, less water molecules can turn to gas. So vapor pressure is lower.

So, the more solute that is added, the lower the vapor pressure.

Français- Marie Raoult discovered that the: 

Vapor pressure of = Vapor pressure of the pure solvent    x    Molar fraction of

       a solution                                                                              Pure solvent

                                                                                         

This is called Raoult's Law. It can only be used when we make a solution with a solute that is non- volatile so it will not turn into a gas.

Colligative Properties

Vapor pressure and intermolecular forces (Maria M, Kristina P, Victor S and Alvaro P).

VAPOR PRESSURE AND INTERMOLECULAR FORCES

In our experiment we used propionic acid (C3H6O2) with a boiling point of 372 K

         

INTRODUCTION

- Materials:

1. Rubber band, Schlenk tube, Stop cock (for the schlenk tube preparation)

2. Bunsen burner (to alter the temperature)

3. Vacuum maker (this will help us only the gas)

4. Gas pressure sensor (to measure the pressure)

5. Adaptor (computer and sensor)

6. Bath (to test temperature)

7. Logger pro (measurement programme)

- Procedure:

1. First, make a perfect schlenk tube, introduce the stop cock in the schlenk tube, put vaseline over it without covering the holes, press it all with the 

rubber band.The air can only pass through the small tube in the left top part.

2. Then use the vacuum maker in the schlenk tube so that there is no air or particle inside.

3. Use the gas pressure sensor to measure the pressure inside the schlenk tube.

4. To measure this we should connect the gas pressure sensor to a computer using the adaptor.

5. Open in your compute the logger-pro, then it should make a graph depending on the different temperatures you apply to the schlenk tube.

6. Introduce the schlenk tube in different baths so that it is exposed to extreme temperatures and the results are shown in the graph done in the logger-pro.

7. Once you’ve finished with the graph, make a table, some conclusions and a complete lab session.

8. Be careful when you separate the different parts of the schlenk tube, the pressure and the vacuum might have join them very strongly and they can broke down.

- Table:

Name of compound	Molecular formula	Diagram of structure	Boiling point (oC)	Temperatures when vapour pressure measured (oC)	Vapour pressure (kPa)	Types of intermolecular forces
Butan-1-ol	C4H10O	*	987	0 22 34 40	5.6 20.3 45.6 59.1	Van der waals, dipole dipole, hydrogen bonding
Butyl acetate	C6H12O2	*	20	0 15 20 40	35,31 32,26 29,41 26,69	Van der waals, dipole dipole, hydrogen bonding
Diethyl ether	(C2H5)2C	*	34,6	20 25 30 35	38,2 44,3 64,5 102,2	Van der waals, dipole dipole
Propyl acetate	C5H10O2	*	102	0 15 20 40	4,33 7,83 9,22 10,07	Van der waals, dipole dipole, hydrogen bonding
Ethyl acetate	C4H8O2	*	77,1	0 15 25 40	9,46 12,18 14,41 20,07	Van der waals, dipole dipole
2-propanol	C3H8O	*	82,5	0 15 29 40	0,53 1,84 3,50 9,82	Van der waals, dipole dipole
pentane	C5H12	*	309,2	0 15 24 35	71,42 98,63 101,93 104,94	Van der waals, dipole dipole
Methyl acetate	C3H6O2	*	-98	0 15 25 35	0,89 9,39 20,59 21,93	Van der waals, hydrogen bonding, dipole dipole

- Results: 

- Conclusion:

Having these results we can claim that the temperature is a very important factor for the molecules and for causing pressure, due to the hitting particles in the container when we heard it, so we can see that this substance (Propionic acid) has a very high BP, and we can check it in the graph.

The main reason for this to happen are the Van der Waals force which interact in the substance caused by the induced dipole of the carbon-hydrogen bonding, the table show us how the organic particles which reacts with hydrogen particles have a high BP, while the substances which have a difference between the lone pairs of oxygen particles with the hydrogen particles have a low BP.

This reaction is caused when the lone pair of particles attracts the hydrogen atoms which would bond with the compound, and it is derived from a strong intermolecular force which interacts with the hydrogen bond, depending on the number of hydrogen atoms the intermolecular force varies.

- References:

Canning, O. (2014). [online] Retrieved from: http://mrcanning10c.wikispaces.com/Topic+3+-+Intermolecular+forces [Accessed: 25 Feb 2014].