Objective – To investigate
the relationship between the molality and the freezing point of a solution.
Hypothesis
I
think that the freezing point of a solution will decrease because like Raoult´s
Law states that the freezing point of a solvent will always decrease when we
add a solute because the process of freezing requires particles of a liquid to
form a regular structure so if we add a solute to the liquid, it becomes more
difficult for the particles to form a regular structure and therefore we must
cool the solution more than normal to achieve a solid state.
Table
of results
Sugar= C12 H22 O11 = 12*12+22+11*16 = 144 + 22 + 176 = 342 Molecular Mass
|
Mass of sugar in solution
(g)
|
Molality
(mol/kg)
|
Attempt 1 - Freezing point (oC)
|
Attempt 2 - Freezing point (oC)
|
Average freezing point (oC)
|
Change in freezing point
compared to pure water (oC)
|
|
0
|
0
|
0
|
0.6
|
0.3
|
0.2 (?
|
|
0.5
|
0.2923
|
0.6
|
0.8
|
0.7
|
0.7
|
|
1.0
|
0.5847
|
0.3
|
0.1
|
0.2
|
0.2
|
|
1.5
|
0.8771
|
1.7
|
1.7
|
1.7
|
1.7
|
|
2.0
|
1.1695
|
2.0
|
2.2
|
2.1
|
2.1
|
|
2.5
|
1.4619
|
2.9
|
2.5
|
2.7
|
2.7
|
Graph
Conclusion
The
results shows that the freezing point variation in the water is higher when there
are more moles in the solution like I have thought in my hypothesis, that the
freezing point will decrease more and more because of the Raoult´s Law so I was
correct in my hypothesis because decreasing the freezing point is the same that
a variation of the temperature.
Evaluation
The
results show a lineal change of variations except when the mass of the sugar is
1.0 mole, so I think that there was an error there (I think it should be about
1.2) also in the first result it shows that the freezing point change is 0.2 ºC
but, in theory, the pure water freeze in 0ºC so that was not pure water. Some
of the improvements that can have the method are that in the method does not
show a method to see if the water is freeze or not so different people could
think about different methods to prove if the water is freeze or not.
References
Sciencesfp.com,. (2015). This area is
password protected [401]. Retrieved 24 March 2015, from http://www.sciencesfp.com/unit-3---colligative-properties.html
Chemwiki.ucdavis.edu,. (2015). Freezing
Point Depression - Chemwiki. Retrieved 24 March 2015, from http://chemwiki.ucdavis.edu/Physical_Chemistry/Physical_Properties_of_Matter/Solutions_and_Mixtures/Colligative_Properties/Freezing_Point_Depression
