Explain the the melting points below and the reason for their disparity.?

Question

Naphthalene has a melting point of 80 degrees Celsius. Explain the different results:

Student 1: 80 - 95 degrees
Student 2: 85 - 92 degrees
Student 3: 79 - 82 degrees
Student 4: 70 - 80 degrees

Which student(s) did the experiment correctly and what possible reasons could the others be in error?

Answer 1

Student 3 has the most reasonable value. Students 1 and 2 probably ran the temperature of the heating block or bath up much to rapidly. Student 4 has results which could be caused by impurities in the sample which he/she may have obtained from some experimental situation.

Answer 2

Maris Stella High School Physics Worksheet (Cooling Curve of Naphthalene)
1
QUICKTIME VR – COOLING NAPHTHALENE
WORKSHEET ON MELTING POINT OF NAPHTHALENE
Name: ___________________________ Index No: _____ Class: _____ Marks: / 20
Instructions: 1. From the iMac Desktop, MacinTosh HD, locate the folder “Learning
Circle’ and open it.
2. Click on the file “CoolingNaphthalene.obj” to run the animation.
3. You are able to use the mouse cursor to control the speed of animation.
Q1) Describe how the solid naphthalene could be safely melted. [2]
The solid naphthalene is placed in a boiling tube. Make sure that the
boiling tube is only half-filled with naphthalene. Place the boiling tube
in a hot water bath, with the water boiling.
Q2) Why is the glass bulb of the thermometer positioned in such a way that it is
entirely surrounded by the molten naphthalene? [2]
This is to ensure that the temperature taken will be accurate. if the
glass bulb is in contact with the boiling tube, the reading will be
inaccurate as certain amount of heat will be lost to the surrounding
through the glass.
Q3) Explain why does the surface of the molten naphthalene solidify first. [2]
The surface of the molten naphthalene is in contact with the air, and
heat is readily lost through convection. Glass is a bad conductor of
heat and therefore, the surface of the molten naphthalene solidify first.
Q4) According to the animation, the temperature of the melted naphthalene is
decreasing even though the surface of the molten naphthalene is solidifying.
Explain? [4]
The temperature recorded depends on where the glass bulb of the
thermometer is located inside the molten naphthalene. For this
animation, it can be clearly seen that the naphthalene surrounding the
glass bulb of the thermometer has started to solidify while the other
regions are still in the molten state. That is why the thermometer
registered a decreasing temperature even though the naphthalene has
not completely solidified.
Maris Stella High School Physics Worksheet (Cooling Curve of Naphthalene)
2
Q5) Draw and label accurately the cooling curve of the naphthalene according to the
animation. [Graph of temperature vs. time, for intervals of half a minute]. The first
picture is shown below with both the time and temperature indicated. [4]
Temperature Time
Q6) Explain the reason for the shape of your graph. [6]
As liquid naphthalene cools, it loses heat to the surroundings and its
temperature falls (curve AB) until it reaches about 80°C. At this point,
naphthalene begins to solidify. Although it is still losing heat to the
surroundings, its temperature remains constant (straight line BC) until
all the naphthalene has solidified (Latent heat of fusion). This
temperature (80°C) is the freezing (melting) point of naphthalene).

think this should be what you are asking and then some:-)

Answer 3

Naphthalene's lit. m.p. as you stated is 80 degrees. Now out of the 4 students I have to say that student 4 is closest to the desired value. During organic chem synthesis mistreaction take place in equilibrium thus not 100% of product is achieved. Secondly, there are side products that are produced, which can be sometimes be an isomer of your desired end product. Whenever determining purity and success of an experiment by using the m.p. then the product usually has a wider range and a depressed m.p., which is the case for student 4. All the other students have a range above the lit.value thus indicating that they probably synthesized a by product.

Answer 4

e=mc2