Procedure: Heat of Combustion of Ethanol and Paraffin Wax

 

Procedure: Heat of Combustion of Ethanol and Paraffin Wax

Materials:

• Aluminum can
• Graduated cylinder (100 mL)
• Digital balance
• Thermometer
• Metal stand and ring clamp
• Wire gauze
• Ethanol (liquid fuel)
• Paraffin wax candle
• Spirit burner or small dish for ethanol combustion
• Matches or lighter
• Heat-resistant gloves
• Stopwatch

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Step 1: Preparing for Ethanol Combustion Experiment

1. Measure Water:

   • Pour 100 mL of water into the aluminum can using a graduated cylinder.
   • Record the initial temperature ($T_i$) of the water using a thermometer.

2. Weigh the Ethanol Burner:

   • Weigh the ethanol burner (or container holding ethanol) before combustion.
   • Record this as Initial mass of burner + ethanol ($m_{\text{initial}}$).

3. Set Up the Calorimeter:

   • Secure the aluminum can with wire gauze on a metal stand.
   • Adjust the height so the ethanol flame will be directly under the can.

4. Burn Ethanol:

   • Light the ethanol and allow it to burn for about 2–3 minutes while stirring the water gently with the thermometer.
   • Ensure the flame only heats the bottom of the can.

5. Measure Final Temperature:

   • Extinguish the flame after 2–3 minutes and immediately record the final temperature ($T_f$) of the water.

6. Weigh the Ethanol Burner Again:

   • Measure and record the final mass of burner + ethanol ($m_{\text{final}}$).

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Step 2: Burning Paraffin Wax

1. Weigh the Candle:

   • Record the initial mass of the paraffin wax candle ($m_{\text{initial}}$).

2. Repeat Steps 1-6:

   • Place the candle beneath the can.
   • Light the candle and allow it to burn for 2–3 minutes while heating the water.
   • Stir the water gently and record its final temperature after extinguishing the flame.
   • Weigh the candle again to find the final mass of the wax ($m_{\text{final}}$).

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Step 3: Calculations

1. Heat Absorbed by Water

Use the formula:

$$q = mc\Delta T$$

where:

• $m$ = mass of water (100 g, assuming 1 mL = 1 g)
• $c$ = specific heat capacity of water (4.184 J/g°C)
• $\Delta T$ = $T_f - T_i$

2. Experimental Heat of Combustion

$$\Delta H_{\text{experimental}} = \frac{q}{\text{mass of fuel burned}}$$

where:

• Mass of fuel burned = $m_{\text{initial}} - m_{\text{final}}$

3. Estimating Accepted Heat of Combustion for Paraffin Wax

Using the ratio:

$$\frac{\Delta H_{\text{accepted (ethanol)}}}{\Delta H_{\text{experimental (ethanol)}}} = \frac{\Delta H_{\text{accepted (wax)}}}{\Delta H_{\text{experimental (wax)}}}$$

Rearrange to find:

$$\Delta H_{\text{accepted (wax)}} = \Delta H_{\text{experimental (wax)}} \times \frac{\Delta H_{\text{accepted (ethanol)}}}{\Delta H_{\text{experimental (ethanol)}}}$$

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Step 4: Sources of Error & Improvements

• Heat Loss: Some heat escapes to the air instead of heating the water.
  • Improvement: Use an insulated calorimeter to reduce heat loss.
• Incomplete Combustion: The flame may produce soot, reducing efficiency.
  • Improvement: Ensure adequate oxygen supply for complete combustion.
• Heat Absorbed by the Can: The aluminum can also absorbs heat.
  • Improvement: Consider accounting for the can’s heat capacity in calculations.