Variations in Boiling Point  

PROJECT LEADER: Ron Peterman, James Bennett High School, Salisbury, Maryland
DATA DESIGN AND SUPPORT: Tom Bulka, Northern High School, Accident, MD

Project Overview

The Boiling/Melting Point Project served as a first effort to involve all MVHS schools in a collaborative project. We solved problems with communication, data collection methods and standards, data reporting form support, and easy access to compiled data and graphs.

We compiled data about altitude, pressure, water boiling point, and naphthalene melting poing for all fifteen Maryland Virtual High School participating schools. It was hypothesized that there would be a measurable difference between Northern High School in Garrett County and the several schools near sea level.

One question that was difficult to answer was whether to encourage submission of repeated measurements (from several students, for example) or of one value from each school. It was decided to accept one value from each school, but that this value should be the one that students at the schools have decided is "closest" to the actual boiling point of water at that time.

Experimental Method



MATERIALS NEEDED: calibrated thermometer, distilled or deionized water, 600-mL beaker if available, boiling chips, heating source (hotplate or burner)

1. The thermometers were calibrated using a 600-mL beaker. The water level was such that when the thermometer was suspended in the water to the immersion line, the bottom of the thermometer was about 2 cm from the bottom of the beaker.

2. Add a few boiling chips (there should be a few in your package - they're just white pieces of porcelain) and heat the water. The thermometer should be suspended in the water to the black immersion line (it's about 7 or 8 cm from the bottom of the thermometer).

3. The water will begin to boil, and after a few minutes the temperature value should level off. If you keep watching the temperature (even for a minute) there will most likely be a small fluctuation in values. You will actually see the temperature go up or down a few tenths. Use the temperature that it appears to center around as your uncorrected boiling point. Try to read the thermometer to the tenths of a degree. To "correct" this boiling point, apply the temperature correction factor that came with your thermometer. Most correction factors are something like "subtract 2.0 oC" from the observed temperature. So, if your observed boiling point is 101.0 oC, and if your correction factor is "subtract 2.0 oC", then the value you would actually report is 99.0 oC.

4. Note the atmospheric pressure in the room when you do your boiling point determination. If you don't have a barometer, or don't trust the one you have, maybe a local airport or weather station can give you the pressure. Now, for the pressure units. It was decided at our meeting to use "millibars" as our unit. Standard atmospheric pressure (i.e. 1.00000 atmosphere) is 1013.25 millibars. If you have the value for atmospheric pressure in inches of mercury (that's what weather stations and airports use), then you divide that value by 0.02953 to convert it to millibars. So, if your pressure is 30.10 inches of mercury, then the value in millibars would be 1019 millibars. If your barometer gives readings in mm of mercury, then to convert to millibars you divide the number of mm of mercury by 0.75006.

5. Find (map, local surveyor, airport) the approximate altitude above sea level for your area. Give the value in meters. To convert from feet to meters multiply the number of feet by 0.3048. (One foot = 0.3048 m.)

6. Once you have the boiling point, atmospheric pressure, and altitude, send the information to the account sent up by Tom Bulka at husky.northern-hs. The exact address and location of the data file will be sent to everyone next week!!!



Materials needed: capillary tube with solid sample, calibrated thermometer, 600-mL beaker, heating source, stirrer (glass rod, spoon)

1. The melting point determination can be done at the same time as the boiling point determination of water. The solid sample we're using has a melting point several degrees below the boiling point of water, so there's time to do both things without them interfering with each another.

2. The 600-mL beaker is filled with enough water so that when the thermometer is suspended down to the immersion line the thermometer bulb is about 2 cm from the bottom of the beaker. If you're going to do the boiling point of water determination at the same time, be sure to use distilled water and boiling chips.

3. The solid sample is contained in the capillary tube. You should have three samples (just in case the first trials don't go well). If the sample has worked its way up the capillary tube, pack it back down in the bottom of the tube by tapping the closed end on a hard surface. When you remove a capillary tube from where it's attached to the thermometer by the rubber band, it's usually easier to take off the rubber band than to try to pull the capillary tube from under the rubber band. (Sometimes when I try to pull the capillary tube from under the rubber band the capillary tube snaps. They're pretty fragile. It's easier to roll the rubber band off the thermometer.)

4. For your first trial you should have one capillary tube attached to the thermometer (by the rubber band) so that the sample is next to the thermometer bulb. Begin heating the water. Gently stir the water to get a uniform temperature around the thermometer bulb. Keep watching the sample. When it begins to melt you will notice some clear liquid next to the solid. Wait until you see some clear liquid before you assume it's melting. As soon as it starts to melt note the temperature (to the tenth of a degree if possible). Keep watching the sample. When it all melts (it usually only takes about 15 seconds to completely melt) note the final temperature. This will give you a temperature range. I was getting about a 1.0 to 1.5 oC range for the samples I tried. Report the temperature range.

5. If for some reason the first trial didn't go well, try another capillary tube. If you miss the reading (it melts and nobody noted the temperature) it's OK to let the sample cool (it reforms a crystal) and redo the procedure with the same capillary tube. Just be sure the water has cooled before you put the thermometer and capillary back in.

6. The capillary and solid sample can be discarded in the trash. The solid is naphthalene.

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