A cooling curve is actually a line graph representing the change in the state of matter of a substance, either from solid to liquid or liquid to solid. In this graph, time is usually represented on the x – axis and temperature on the y – axis. The particles in the wax in the solid state slowly start to get more energy when heated and start to move more rapidly at a certain temperature and then change to liquid. When it has to change from liquid to solid, the particles in the wax start to lose energy and come close together till they become solid.
VARIABLES: Independent Dependant Controlled Temperature change Time taken for wax to solidify Environmental change, amount of wax taken. APPARATUS: > Boiling tube > Beaker –> 250 cm3 (i? 25 cm3) > Thermometer –> range – 10i? C to 110i? C (i? 0. 5i? C) > Clamp stand > Bunsen burner > Tripod stand > Wire gauge > Paraffin wax > Water for water bath (in beaker) > Stopwatch –> (i? 0.
1 seconds) METHOD (GIVEN): 1) Heat half a beaker of water to about 90i? C. 2) Clamp a boiling tube with paraffin wax in it and put it in hot water with the thermometer.
3) Measure the temperature of molten wax and start your stopwatch. 4) Record the temperature at suitable time intervals till all the wax solidifies completely. 5) Present your results suitably and interpret these in terms of the concepts you’ve learned so far. OBSERVATIONS: Amount of water (ml) Initial Temperature (Trial 1) (i? C) Initial Temperature (Trial 2) (i? C)
Water Temperature (i? C) Time intervals (s) Temperature (Trial 1) (i? C) Temperature (Tria C respectively, it started to go clear gradually, until it melted completely at 62.
5i? C and 63. 0i? C respectively at which point, it was completely transparent. As it start freezing, at 48. 0i? C and 50. 5i? C respectively, it started to gain its original greyish colour and it froze completely at 50. 0i? C and 53. 0i? C respectively, it was completely opaque. GRAPHS: Trial 1: Trial 2: ANALYSIS:
From the above graphs, we can see that the temperature of the wax in the test tube keeps falling until a certain point where it becomes a constant value and then continues to fall. The particles of wax that are held together by weaker intermolecular forces need to a particular temperature at which all the bonds can become stronger so as to change its state. When heat is taken away from a liquid substance, the energy supplied to it drops and thus, the particles do not have enough energy to collide with each other and move far apart. Thus, the particles come closer to each other and the intermolecular forces become stronger.
The temperature required for bonds to form in a particular substance is the same for all particles in that substance and thus, the temperature of the wax remains constant throughout a certain period when all bonds are formed, changing the state of the substance. This shows that the wax used in the experiment was a pure substance as it has been proven that a substance is pure only if its melting/boiling point is a constant. The temperature fell rapidly in the initial stages because very few bonds or no bonds could be formed due to such a high temperature.
Later, as the temperature drops, the numbers of bonds formed become comparatively higher and thus, the temperature starts to fall slowly. Once the whole substances solidifies, all the bonds have been formed and thus, the particles of the substance have a very low energy because of which they can’t collide and generate heat. Thus, the temperature of the substance continues to fall. POSSIBLE SOURCES OF ERROR: > The reading taken from the thermometer may not have been completely accurate throughout the experiment. > As the experiment was conducted in an air-conditioned room, this could have affected the experiment.
> The time taken from the stopwatch wouldn’t be completely accurate. CONCLUSION: From this experiment, we can conclude that the temperature required for bonds to form in a particular substance is the same for all particles in that substance. This rule applies to all pure substances as all particles in a pure substance are the same and thus, they bond at the same temperature, as in this experiment. An impure substance would contain other substances and thus, the particles would bond at different temperatures and the boiling/melting point wouldn’t be a constant.