Science 7–10 · Year 8
Energy from a burning fuel: heating water with a spirit burner
Change
School laboratory, not for home
In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.
The idea
Burning a fuel transfers energy to its surroundings; the temperature rise of a fixed mass of water shows how much of it reaches the water, and the flame also heats the air and the apparatus, so only part of the energy is captured.
Safety card
Setting: In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.
Hazards
- ethanol and methylated spirits are highly flammable; the burner can flare when refilled
- methylated spirits burns with a nearly colourless flame that is hard to see (CSIS Appendix F)
- hot flask and thermometer
- methylated spirits contains methanol, which is toxic; learners do not handle the fuel
Controls
- teacher fills and caps the burners; never refill a warm burner
- no more than 20 mL of fuel per group for the whole activity (CSIS Volume 2 Figure D-6 limit for flammable liquids used in a reaction by Years 7 to 12, per student or group per activity), so a group comparing two fuels fills each burner with no more than 10 mL; a run uses only part of this
- eye protection, hair tied back, bench clear of paper
- burner extinguished by capping, never blown out
Note
NSW Department of Education, Chemical Safety in Schools (CSIS) 2021 Technical Update: Section 1.7 (risk assessment before use) and Volume 2 Appendix D (generic assessment advice, user codes and DoE categories). Complete a RiskAssess or CSIS site-specific risk assessment before the lesson. CSIS Appendix F lists methylated spirits under chemicals to be used with caution.
What you need
- spirit burner with cap, filled by the teacher with no more than 20 mL of ethanol or methylated spirits (95 percent ethanol, 5 percent methanol, as CSIS describes it)
- conical flask or copper calorimeter with 100 g of cold tap water, clamped 5 cm above the wick
- thermometer to 0.5 °C, balance reading to 0.01 g, heat-resistant mat, draught shield
How to do it
- Weigh the capped burner. Record the starting temperature of the 100 g of water.
- Light the burner under the flask and stir the water gently with the thermometer until the temperature has risen by about 40 °C; cap the burner at once.
- Reweigh the capped burner and find the mass of ethanol burnt.
- Calculate the temperature rise of the water for each gram of fuel burnt and compare it with the class. List where the rest of the flame's energy went.
What you should see
The water warms steadily while the burner loses mass. Much of the flame's energy heats the air, the flask and the clamp rather than the water: the set-up is an open system that transfers energy to its surroundings, and soot under the flask shows some combustion was incomplete. The learner knows it worked when repeat runs give similar temperature rises per gram of fuel and the learner can name where the rest of the energy went.
What changes
- What you change
- fuel (ethanol; propan-1-ol or butan-1-ol as a follow-on)
- What you measure
- temperature rise of the water per gram of fuel burnt
- What you keep the same
- mass of water
- height of flask above the wick
- temperature rise aimed for
- draught shield in place
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- All the energy from the flame goes into the water.
- A fuel that burns with a bigger flame releases more energy per gram.
- The mass of the burner falls because the alcohol evaporates, not because it burns.
Curriculum references
The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.
- Science 7–10 Syllabus (2023)SC4-CHG-01SC4-WS-06
- Australian Curriculum v9AC9S8U07AC9S8I05
Sources
The pages the author read to write this activity.