The Calorimeter Lab is from Ian Guch’s 24 Lessons that Rocked the World and it involves building a calorimeter, bascially an insulated container, and measuring the heat of solvation for sodium hydroxide. I had styrofoam cups, newspapers, aluminum foil, bubble wrap and some insulated paper cups with lids out for the students to build their calorimeters. They had to make sure it could hold 200 ml of distilled water, a thermometer and that they could easily put in the sodium hydroxide (NaOH) pellets. Students measured the temperature of the water before dropping in the pellets (4 grams of NaOH) and then every 20 seconds until the temperature stabilized.
Students graphed their data, temperature as a function of time and calculated the heat of solvation (heat given off as sodium hydroxide dissolved in water) by using Δ H = mc Δ T, where m is the mass of the water in the calorimeter, c is the specific heat capacity of water (4.184J/g°C)and ΔT is the temperature change. We discussed this formula a bit before doing the lab. The heat energy that is released in dissolving NaOH goes into heating the water in the calorimeter and the more water you have the more energy you will need. The greater the temperature change, the greater the heat energy required. Its also easier to change the temperature of some things, like copper, while its difficult to change the temperature of water. So to calculate the heat required to change the temperature of something you need to know its specific heat capacity – the heat energy required to raise the temperature of 1 gram of that substance by 1°C.
For this experiment we expected to get results that were a little below the predicted value, showing that we actually lost heat to the surroundings and our calorimeters weren’t perfect. But everyone ended up with results on the high side and we couldn’t figure out what went wrong. We suspected that the pocket scale we used to measure the 4 grams of NaOH pellets might have malfunctioned, but checking it with known masses and a triple beam balance it appeared to be working correctly. Everyone confirmed that they used the correct amount of water, filling two 100 ml graduated cylinders with distilled water. We calibrated our thermometers a few weeks ago so I don’t think they were the problem. I would have liked to repeat the lab, but we used up all our sodium hydroxide – which is another reason I suspected our scale because we should have had some left over.
The only dangers with this lab are the NaOH pellets and making sure to neutralize the NaOH solution with vinegar at the end of the lab before dumping down the sink. I used some left over cabbage juice indicator so I would know when the solution was neutral. Instructions for this are included in the lab handout.
Students watched the following Crash Course Chemistry videos before class: