Unit 3 Chemistry – Heat Content of a biscuit

Part A – Heat content of propane

Name ______Partner ______

Aim:

To experimentally determine the heat energy of propane.

Materials:

  • retort stand
  • boss head and clamps
  • 125 mL metal can
  • weighing balance
  • data logging software and computer
  • click igniter / long matches
  • 100 mL measuring cylinder
  • stop watch
  • ruler
  • propane canister
  • distilled water

Risk Assessment:

Use the Risk Assess program to generate a risk assessment for this experiment. Complete Table 1.

Table 1: Risk Management

Risks / Safety Precautions

Signature ______Date ______

Method:

  1. Weigh the empty metal can
  2. Add 100 mL of distilled water to can and reweigh
  3. Weigh the propane canister
  4. Set up the apparatus as follows:

(Image adapted from: VCAA (2016) Unit 3 & 4 Chemistry Exam 8thNovember p. 38)

  1. Measure the initial temperature of the water
  2. Light the propane and burn for 5 minutes
  3. Measure the final temperature of the water (it may beafter the flame has been extinguished)
  4. Allow propane canister to cool, then reweigh.

Results:

Record all results, observations and calculations in Table 2. Show all working in your calculations.

Table 2. Results and observationsDate ______

Mass of empty can (g)
Mass of can + water before combustion (g)
Mass of water (g) – m(water)
Mass of propane canister before heating (g)
Mass of propane canister after heating (g)
Mass of propane combusted (g)
Initial temperature of water (oC)
Final temperature of water (oC)
ΔT(water) (oC)
Energy transferred to water (J)
E = m x c x ∆T
Where
mass = m(water) (g)
c = 4.18 J g-1oC-1
ΔT(water) oC
Energy transferred to water in kJ (E)
(1 kJ = 1000 J)
n(propane) combusted (mol)

Experimental molar heat of combustion of propane, ΔHc (kJ/ mol)
Where

Discussion:

  1. Identify the variables in this experiment.

Independent variable
(the factor being studied / deliberately changed in experiment) / Dependent variable
(what you measured / observed) / Controlled variables
(what you would keep the same if you repeated the experiment)
  1. Write the balanced thermochemical equation for the complete combustion of propane.

______

  1. Compare your experimental value with the theoretical value of propane.

Experimental value ΔHc propane / Theoretical value ΔHcpropane
-2217 kJ mol-1
  1. Calculate the percentage of energy lost to the environment in your experiment.

% energy lost to environment = (theoretical value of ΔHc – experimental value of ΔHc)

theoretical value of ΔHc

______

______

  1. Analyse and evaluate your findings by completing the following table.

Limitations of method / Proposed improvements to the method

Part B – Heat content of a biscuit

Aim:

To experimentally determine the heat energy of a biscuit in kJ g-1.

Materials:

  • retort stand
  • boss head and clamps
  • 125 mL metal can
  • weighing balance
  • data logging software and computer
  • click igniter
  • 100 mL measuring cylinder
  • cork
  • paperclip
  • 10 x 10 cm2piece of aluminium foil
  • biscuit

Risk Assessment:

Use the Risk Assess program to generate a risk assessment for this experiment. Complete Table 3.

Table 3: Risk Management

Risks / Safety Precaution

Signature ______Date ______

Method:

  1. Bend a paper clip and insert it in a cork as shown
  1. Weigh the cork, paper clip, biscuit and aluminium foil
  2. Use a clamp to hold the cork and biscuit under the can (same distance from biscuit to can as the propane flame was to the can in part 1)
  3. Place the aluminium foil underneath the biscuit (to catch drips)
  4. Measure the initial temperature of the water
  5. Ignite the biscuit (this may take 30+ seconds)
  6. Measure the final temperature of the water once the biscuit has completed burning
  7. Weigh the cork, paper clip, charred biscuit and aluminium foil

Results:

Record all results, observations and calculations in Table 2. Show all working in your calculations.

Table 4. Results and observationsDate ______

Comments / observations
Brand of biscuit
Energy content of biscuit (on product label) kJ / 100g
Mass of cork, paper clip, biscuit and aluminium foil before combustion (g)
Mass of cork, paper clip, biscuit and aluminium foil after combustion (g)
Mass ofbiscuit combusted (g)
Mass of water (from Table 2) (g)
Initial temperature of water (oC)
Final temperature of water (oC)
ΔT(water) (oC)
Energy transferred to water (J)
E = m x c x ∆T
Where
mass = m(water) (g)
c = 4.18 J g-1oC-1
ΔT(water) oC
Energy content of biscuit kJ / gassuming no energy lost to environment
Energy content of biscuit kJ / 100 g
assuming no energy lost to environment
Use your findings from Parts 1 and 2 to calculate a more accurate value of the energy content in the biscuit kJ / 100g

Discussion:

  1. Compare your experimental value with the theoretical value of energy content biscuit

Experimental energy content biscuit kJ / 100g / Label declaration energy content biscuit kJ / 100g
  1. Analyse and evaluate your findings by completing the following table

Limitations of method / Proposed improvements to the method

Conclusion:

______

______