The Edexcel core practical: heating water with a spirit burner of ethanol, propanol, butanol and pentanol, working out the energy released per gram, and explaining the trend and why the results come out low.
What you will learn
- Name the variables and plan the practical
- Calculate the energy released per gram from a temperature rise and a mass burned
- Describe and explain the trend from ethanol to pentanol
- Explain why the results are lower than data-book values and how to improve them
What you do
A spirit burner of the alcohol heats water in a copper can clamped just above the wick.
- Measure a fixed volume of water (say 100 cm³, which is 100 g) into the can and record its temperature.
- Weigh the spirit burner with its cap on.
- Light it and heat the water, either for a fixed time or until the temperature has risen by a fixed amount (say 20 °C). Then put the cap on to put it out.
- Reweigh the burner straight away: the difference is the mass of alcohol burned.
- Repeat with each alcohol, using fresh water and the same can and height.
- Independent variable: the alcohol (how many carbon atoms it has).
- Dependent variable: the temperature rise (fixed time) or the mass burned (fixed rise).
- Control variables: the mass of water, the height of the can above the wick, the can, the starting temperature.
Safety: the alcohols are flammable. Keep the bottles closed and away from the flame, stand the burner on a heatproof mat and wear eye protection. The can gets hot: let it cool or move it with tongs.
The rest of this lesson and its 9 practice questions are locked.
In this lesson
- What you do
- Energy per gram
- The trend, and why the results are low
- Try it: The variables first
9 practice questions, marked as you go; about 20 minutes in all.
In this unit: Organic chemistry
Crude oil and the alkanes, combustion and cracking, then alkenes, alcohols, carboxylic acids, esters and polymers for separate Chemistry, with the formula and mass calculations that go with them.