CSEC Physics Lab - Cooling curve of candle wax
Download as DOCX, PDF4 likes19,167 views
1. The document describes an experiment to investigate the cooling curve of candle wax by heating it until melted and then measuring its temperature every 30 seconds as it cooled. 2. The melting point of candle wax was determined to be 53.5°C as the temperature remained constant for 3 minutes during the solidification process. 3. According to the kinetic theory, particles in solids vibrate in place while liquid particles can move freely, explaining why brown flakes in the wax remained still after solidification.
CSEC Physics Lab - Cooling curve of candle wax
- 1. RonaldoDegazon Wednesday09/05/12 Physics:Lab#8 Thermal Physics Aim: To investigate the coolingcurve of asubstance. Apparatus: candle wax,testtube,testtube holder,Bunsenburner,tripod&beaker,thermometer, stop-clock,retortstand, water& wire gauze,glassrod Diagram:
- 2. Procedure: 1. The apparatus wasset upas shownin DiagramA, withthe substance ina water bath. 2. The substance washeateduntil itwascompletelymeltedandwell above itsmelting point. 3. The test tube containingthe substance wasremovedandplacedinaretortstand, withthe thermometerinthe liquidasshowninDiagramB. 4. The stop-clockwasstartedand the temperature wasrecordedeveryhalf minute until itfell towell below itsmeltingpoint.The thermometerwasnotremoved duringsolidification. 5. The substance wasre heatedtoa temperature above itsmeltingpointsothe thermometercouldhave beenremovedfromthe substance. 6. A coolingcurve of F versust wasplottedforthe substance. Results: Time / s Temperature / o C 30 62 60 59.5 90 57 120 56.5 150 55 180 54.5 210 54.5 240 54 270 54 300 53.5 330 53.5 360 53.5 390 53.5 420 53.5 450 53.5 480 53.5 510 53 540 52.5 570 52.5 600 51 630 51 Time / s Temperature / o C 660 50.5 690 50 720 50 750 49.5 780 49 810 48.5 840 48 870 47.5 900 47
- 3. Discussion: The meltingpointof a substance is the temperature at which it changes from a solid to liquid. Also the process in which a liquid turns into a solid is called solidification which occurs at the freezingpoint;the exactopposite of the melting point. When a substance solidifies, the heat released during that process is called the latent heat of solidification. From the experiment, it was deduced that the melting point of candle wax was 53.5 o C because itremainedatthat temperature for 180 seconds.Heatwas being lostduringthatperiod butthe temperature did not fall at all. Therefore it was concluded that the heat was no lost but was used to repair the bonds of the molecules. The heat used during that 180 seconds is its latent heat of solidification. Dark brown flakes were noticed moving around in the candle wax when melted. However,whensolidified,these flakesremainedstill.Thiscanbe accountedforwiththe Kinetic Theory. The theorystatesthat liquidsconsistof clustersof particlesthatare free tomove and that solids consist of fixedparticleswhichare restricted from moving but only vibrate about a fixed point. When the wax was melted,the brownflakesmovedaroundfrombeingbombardedbythe movingclustersinthe liquid wax.However,whenthe wax solidifiedthere wasnomovementamongstthe particlesand so the flakes no longer moved. The KineticTheory can alsobe usedto explainthe shape of the graph.First it states that all matter is made of tiny particles. It goes on to say that these particles when supplied with energy, move fasterandhence theiraverage kineticenergyincreases.Average kinetic energy is proportional to temperature, hence the more heat supplied the higher the temperature. Applying the theory to this experiment,youcouldsaythatthe more heat releasedbythe candle wax, the lower its average kinetic energy fell and hence the lower its temperature dropped. From points A to B, as more heat was released by the candle wax, the lower its temperature fell hence the downwards trend in the line. However, from B to C the line remained straight– the wax’stemperature remainedconstant. Thisissimplybecausethe beinglostwasnot being absorbedbythe wax’ssurroundings,itwasbeingusedto repair the bonds of the molecules, hence the average kineticenergyof the particlesdidnotfall.Nevertheless,whenthe bondswere repaired and the wax had solidified,the surroundingsresumedabsorbingthe heatfromthe wax,hence from C to D there is another downward trend. Sources of Error: - Human ReactionTime:there wasa possibilitythat the temperature reading was not taken exactly 30 seconds after the previous reading. - Parallax Error: there was a possibility of a parallax error when reading the scale of the thermometer.
- 4. - There wasthe possibilitythatthe wax wouldhave meltedtooquicklyandvaporized. - There wasa possibilitythat the thermometer would take the reading of the tube’s temperature and not the wax’s. Precautions: - To reduce parallax error, the thermometer reading was taken with the eye perpendicular to the level of liquid in the thermometer. - The test tube containing the candle wax was heated indirectly in a water bath to control the rate at which it was heated so that it didn’t melt too quickly. - It was ensured that the thermometer did not touch the bottom of the test tube to ensure that the temperature of the wax was taken and not the tube. - A glass rod was used to stir the water to ensure that its temperature remained uniform throughout. Conclusion: A cooling curve was successfully obtained for candle wax.