Question

In a lab, using a styrofoam cup as a calorimeter is an experimental limitation. Why? how could this be fixed?

Answer 1

Answer -

A calorimeter is a device used to measure the quantity of heat flow in a chemical reaction. Two of the most common types of calorimeters are the coffee cup calorimeter and the bomb calorimeter.

A coffee cup calorimeter is essentially a polystyrene (Styrofoam) cup with a lid. The cup is partially filled with a known volume of water and a thermometer is inserted through the lid of the cup so that its bulb is below the water surface. When a chemical reaction occurs in the coffee cup calorimeter, the heat of the reaction is absorbed by the water. The change in the water temperature is used to calculate the amount of heat that has been absorbed (used to make products, so water temperature decreases) or evolved (lost to the water, so its temperature increases) in the reaction.

The role of the Styrofoam in a coffee cup calorimeter is that it reduces the amount of heat exchange between the water in the coffee cup and the surrounding air. The value of a lid on the coffee cup is that it also reduces the amount of heat exchange between the water and the surrounding air. The more that these other heat exchanges are reduced, the more accurate results can be obtained. Any error analysis of a calorimetry experiment must take into consideration the flow of heat from system to calorimeter to other parts of the surroundings. And any design of a calorimeter experiment must give attention to reducing the exchanges of heat between the calorimeter contents and the surroundings.

Experimental limitation -

A coffee cup calorimeter is great for measuring heat flow in a solution, but it can't be used for reactions which involve gases, since they would escape from the cup. The coffee cup calorimeter can't be used for high temperature reactions, either, since these would melt the cup.

Human error - reaction mixture not mixed fast enough, holding the cup, heat from hands affects heat measurement, did not pour in the substance all in one go, spillage from cup.

To overcome limitations - A bomb calorimeter is used to measure heat flows for gases and high temperature reactions. A bomb calorimeter works in the same manner as a coffee cup calorimeter, with one big difference. In a coffee cup calorimeter, the reaction takes place in the water. In a bomb calorimeter, the reaction takes place in a sealed metal container, which is the bomb vessel, then placed in an insulated container (polystyrene insulation). Heat flow from the reaction crosses the walls of the sealed container to the polystyrene. The temperature difference is measured, just as it was for a coffee cup calorimeter. Analysis of the heat flow is a bit more complex than it was for the coffee cup calorimeter because the heat flow into the metal parts of the calorimeter must be taken into account.

Conclusion

In conclusion the bomb calorimeter is more accurate and leaves less room for human error. It is faster and excludes environmental variables that may not have been considered. It also gives you the energy content of the substance being burned, which means that you do not have to calculate it.