Download 85. Comparing the heat energy produced by combustion of various

Classic chemistry experiments
85.
219
Comparing the heat energy
produced by combustion
of various alcohols
Topic
Exothermic reactions, bond formation, bond breaking, heats of reaction/combustion.
Timing
60 min.
Description
Students use the combustion of known amounts of various alcohols to heat a known
amount of water.
Apparatus and equipment (per group)
▼ Retort stand
▼ Boss
▼ Clamp
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▼ 250 cm Conical flask or metal calorimeter
▼ Thermometer
▼ Spirit burners.
Chemicals (per group)
Methanol (Highly flammable)
Ethanol (Highly flammable)
Propanol (propan-1-ol) (Highly flammable)
Butanol (butan-1-ol) (Highly flammable).
Teaching tips
Stress the importance of fair testing, for example the height of the calorimeter above
the wick. More able students can work out the number of moles used and find the
energy produced per mole. A temperature sensor attached to a computer can be used
in place of a thermometer. It can plot the temperature change on a graph and allow
better quantification of the heat produced.
Background theory
Energy changes, exothermic and endothermic reactions, reactions involving bond
breaking and bond formation. For more advanced students bond enthalpies.
Energy change = mass of solution x specific heat capacity x temperature change.
Safety
Wear eye protection. Spirit burners are the safest way of burning the alcohol but
students should not be allowed to fill them. Use spirit burners with a wide base. Spirit
burners should be filled by a technician in the preparation room and labelled. No stock
bottles of alcohol should be allowed in the laboratory.
Answers
1. Butanol.
220
Classic chemistry experiments
Comparing the heat
energy produced by
combustion of various
alcohols
Introduction
The combustion of alcohol produces energy. This experiment compares the amount of
heat produced by the combustion of various alcohols.
Thermometer
Clamp
Conical flask
Spirit burner
Alcohol
What to record
Alcohol
Initial
temp/°C
Final
Temp
Initial
temp/°C change/°C mass/g
Final
mass/g
Mass
used/g
Methanol
Ethanol
Propanol
Butanol
What to do
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1. Fill the conical flask with 100 cm of water. Clamp the flask at a suitable height so
that the spirit burner can be easily placed below.
2. Weigh the spirit burner (and lid) containing the alcohol and record the mass and
name of the alcohol.
3. Record the initial temperature of the water using the thermometer.
4. Place the spirit burner under the conical flask and light the wick.
Classic chemistry experiments
221
5. Allow the alcohol to heat the water so the temperature rises by about 40 °C.
6. Replace the cap to extinguish the flame.
7. Reweigh the spirit burner and cap and work out the mass of alcohol used.
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Repeat for different alcohols. Use 100 cm of new cold water each time.
Safety
Wear eye protection. Do not open the spirit burner.
Question
1. Which fuel provides the most energy per gram?