Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

CHEMISTRY · Stage 8 · Chapter 9: Chemical Reactions 2

Chemistry 9.4 Investigating fuels — Spirit Burners and Fair Testing

5 min read 6 parts Lesson 4 of 12

0%read
Lesson summary

9.4 Investigating fuels — Spirit Burners and Fair Testing — Alhussan International Academy — Chemistry (Stages 7–9) notes: Plan, carry out and analyse a fair test to compare the energy released by different fuels.Fuel = a substance that burns to release useful energy, mostly as h…

  • Combustion
  • Comparing fuels
  • Testable question
  • Independent variable
  • Control variables
  • Calculations

Part 1 of 6Fuels and energy release

  • Fuel = a substance that burns to release useful energy, mostly as heat.
    • Common fuels include methane (natural gas), ethanol, propanol, butanol, wood, coal and hydrogen.
  • Combustion — burning a fuel in oxygen is an exothermic reaction, so chemical energy stored in the fuel is transferred to the surroundings.
  • Comparing fuels — different fuels release different amounts of energy per gram, so they are compared by burning the same mass and measuring the effect on a fixed amount of water.

Part 2 of 6Choosing a scientific question

  • Questions"Which fuel makes water hottest?", "Which fuel is cheapest?" and "Which fuel is best?"
  • Testable question"Which fuel makes water hottest?" can be answered by a fair test because changing one variable affects another.
  • Too broad"Which fuel is best?" cannot be answered by one test, because "best" depends on cost, safety, pollution and other factors.

Part 3 of 6Variables

  • Independent variable — the type of fuel.
  • Dependent variable — the temperature change of the water.
  • Control variables — the mass of fuel burned and the volume of water.
    • Also keep the starting temperature of the water, the distance between flame and can, and the type and size of can the same.

Part 4 of 6Method with a spirit burner

  1. Set up the clamp stand with a metal container holding the water and a thermometer, above a spirit burner holding the fuel.
  2. Measure out 100 cm3 of water and record its temperature with the thermometer.
  3. Light the burner and heat the water, stirring.
  4. When 1 g of fuel has burned, put out the flame with the cap.
  5. Record the new temperature.
  6. Repeat three times for each fuel, and calculate the mean.
  • Calculations — mass of fuel burned = start mass - end mass, and temperature change = final temperature - start temperature.
    • Energy transferred to the water = mass of water × 4.2 × temperature change (in J).
    • A larger temperature change for the same mass of fuel shows that more energy was transferred to the water.
  • Safety — tie back hair, wear eye protection, keep flammable liquids away from flames and put out the burner with its cap.
  • Accurate thermometer readings — keep the bulb in the water, not touching the bottom of the container, and wait for the reading to settle.

Part 5 of 6Presenting and analysing evidence

1Results table
— put the independent variable (fuel) in the left column and include a unit in the other column headings.
2Repeats1 point
— if the three values are similar, the data are reliable.
  • Without repeats an anomalous result would not be spotted.
3Anomalous result1 point
— in Fatima's data the first ethanol measurement was very different from the other two, so she repeated it once more.
  • The new value of 43 °C was close to the others, giving a mean for ethanol of 41 °C.
4Precision
— three butanol results of 55 °C, 57 °C and 53 °C are close together, so the data are precise.
5Conclusion2 points
— ethanol had the smallest mean temperature change, so it transfers the least thermal energy.
  • Propanol and butanol increased the water temperature more, so they transfer more energy than ethanol.
  • No scientific reason is included if it has not been learnt yet.
6Per gram
— if different masses burn, divide the energy by the mass burned, because the fuel with the biggest temperature rise may simply have burned more.

Part 6 of 6Evaluating the method

  • Why results are low — much of the energy is lost to the air, to the metal container and to the surroundings, so the water gains less energy than the fuel released.
  • Incomplete combustion — it releases less energy and makes soot and carbon monoxide.
  • Improvements — shield the flame with a draught shield so more energy goes into the water.
    • Use a lid on the can, a copper can that conducts heat well, and a shorter distance between flame and can.
    • Repeat each fuel three times and calculate a mean to reduce random errors.
  • Trend in alcohols — the longer the carbon chain, the more energy is released per gram.

Last updated: