martes, 24 de marzo de 2015

Freezing point depressions for solutions of sugar in water


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



1 comentario:

  1. Raolt´s Law is to do with vapour pressure not FP.

    Always give a table a title.

    Good graph but please use a line of best fit when we are investigating patterns.

    Conclusion could have used theoretical values to compare with your results.

    The evaluation contains almost no relevant problems or solutions.

    4/8 --> 5

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