I'm doing a lab and we used naphthalene.

Here's some data:

Mass empty test tube:30.967g
Mass test tube plus naphthalene:40.545g
Mass naphthalene taken:9.578g
Freezing point of naphthalene (from graph)

As for the freezing point of naphthalene, how do I get it? It says from graph, but which graph? I know I'm supposed to plot a graph with the temperature vs the time in C... but where in the graph do I get it? Here's my times and temperatures just in case they're needed...

Time in Minutes and Seconds Temperatures in ○C
0:30 95.1
1:00 88.7
1:30 84.5
2:00 80.9
2:30 79.3
3:00 79.3
3:30 79.4
4:00 79.3
4:30 79.2
5:00 79.3
5:30 79.2
6:00 79.2
6:30 79.1
7:00 79.1
7:30 79.0
8:00 79.0
8:30 798.0
9:00 78.7
9:30 78.6
10:00 78.4
10:30 78.1
11:00 77.6
11:30 77.4
12:00 76.6
12:30 75.6
13:00 74.4
13:30 72.9
14:00 70.7
14:30 68.5
15:00 66.1
15:30 63.6

How do I get the freezing point of naphthalene?

When freezing occurs, the temperature remains constant. As soon as there is no more freezing, the temperature falls continue to fall down. So, from your graph, you have to look for the temperature for which the temperature remains constant for the longest period.

Based on your numbers alone it may be hard to figure out the freezing point correctly. Did you observe changes in the solution ? First appearance of cloudiness [that's basically parts of the solution freezing to form crystal] should correspond to the freezing point [because after that the substance will just change state]. Unknown008's answer is correct. [If you do the experiment again you want to take the temperature readings more frequently say 10s or 15s].

I think that the naphthalene might be impure, hence explaining the long range of temperature, but I see that the temperature at which the naphthalene remains constant for the longest period is 79.2, 79.1 and 79.0, giving an average of 79.1. So, if it were me, I would have said that 79.1 is the freezing point of the sample of naphthalene.

You both were right I turned it in and took your advice and did very well I want to thank the both of you so much.