EXPERIMENT: OBSERVATION OF A PHASE CHANGE
These supplies are needed:
- test tube with 12-15 grams paradichlorobenzene (PDCB) (moth crystals) (Not suggested if you do not have access to a fume hood or good ventilation system to perform. Paraffin wax may then be used in place of PDCB.)
- text tube with 12 - 15 grams of paraffin wax. (substitute for PDCB)
- three Pyrex beakers the same size, 150 mL to 500 mL range
- two 250 mL Pyrex beakers
- two thermometers
- beaker stand
- heat source
- three dye tablets or egg-coloring tablets
Unit 1 of this course gave you an opportunity to improve your skills of observing and hypothesizing. Unit 2 provides you opportunities to use these improved skills to study the nature of matter. Matter comes in three normal physical states called phases. These states of matter are called solid, liquid, or gas. The basic difference between the solid, liquid, or gaseous state of any substance is the amount of the energy the substance contains. Energy change in a system can occur in many ways and, depending upon the system, will display varying characteristics.
One way to study energy is to study the melting and cooling characteristics of a pure substance. In looking at these phase changes, we can see the result of adding energy and its effect on the temperature of the substance changing phases. We will be studying this phenomenon using PDCB or paraffin wax. .
In "processing" the data obtained in this experiment, we will be using an important tool. One of the best ways to handle numerical data of the type we will collect is to graph it. Graphing gives us a visual picture of what has happened and is very useful in observing important changes. For the graphs in this lab, plot the temperature on the y-axis (vertical axis) and the time on the x-axis (horizontal axis). This sample graph shows roughly the shape of the curve that should develop from your data in this lab.
Has any of y'all done this or would know the answer?
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Paraffin wax is a white or colourless soft solid that is derived from petroleum and consists of a mixture of hydrocarbon molecules containing between twenty and forty carbon atoms. It is solid at room temperature and begins to melt above approximately `37^oC.`
When a certain mass of paraffin wax is heated, the different alkanes reach
their melting telmperatures at different point of time and during the melting
process, the time vs. temperature graph should exhibit flat pattern. However, a
steep rise in temperature is expected hen no phase change is taking place.
Since there are many alkanes present in paraffin, its heating graph should exhibit a
zigzag pattern (see the attached figure).
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