Core Practical: Heat of Combustion of Alcohols Flashcards

All 6 cards in this deck

What are the steps in the core practical to compare the temperature rise produced by burning different alcohols?
e.g. burning ethanol under $100\ \mathrm{cm^3}$ of water

1. Measure $100\ \mathrm{cm^3}$ of water into a metal calorimeter and record its starting temperature
2. Weigh the spirit burner containing ethanol, light it and heat the water, stirring
3. Put out the flame, record the final temperature and reweigh the burner; repeat with propanol, butanol and pentanol

Which measurements must be recorded in the alcohol combustion core practical?

Volume (or mass) of water, initial and final water temperature, and mass of the spirit burner before and after burning.

Apart from the volume of water, name two variables that must be kept the same when each alcohol is burned.

Distance from the flame to the container, and the length of the wick (also the same container and same starting temperature).

What is the main source of error in the alcohol combustion practical?

Heat lost to the surroundings and the apparatus instead of heating the water.
Incomplete combustion and evaporation of alcohol also reduce the result.

Give two improvements to the alcohol combustion practical.

Use a draught shield/screen and insulate the container (also use a copper calorimeter and a lid).

True or false? The energy released per gram calculated from this practical is usually higher than the accepted data-book value.

False. It is usually lower, because energy is lost to the surroundings and combustion may be incomplete.