Molar Heat of Combustion

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Heats of Combustion of Alkanols

Aim: To perform a first-hand investigation to determine the heats of combustion of selected alkanols. Hypothesis: It was predicted that methanol would have the highest molar heat of combustion, decreasing as the chains become longer. Equipment:

• Three spirit burners containing methanol, ethanol and propan-1-ol respectively • Electronic scales
• Water
• 100ml measuring cylinder
• Retort stand and boss-head clamp
• Copper beaker
• Thermometer
Method:
1. All three of the spirit burners were weighed separately and their masses recorded. 2. 100ml of water was measured out and placed in the copper beaker, which was then suspended with the boss-head clamp above the methanol spirit burner. The thermometer was placed in the beaker and the temperature was recorded. 3. The methanol spirit burner was lit, and the temperature raise in the water was observed until a 10 oC rise in the original temperature was noticed. The spirit burner was then extinguished. 4. The spirit burner was re-weighed and the mass again recorded to determine the mass loss. 5. Steps 2-4 were repeated with each of the other spirit burners. 6. Results were collected and used to determine the molar heat of combustion for each of the alkanols. Results:

|Alkanol |Initial Mass (g) |Final Mass (g) |Mass Change (g) | |Methanol |176.5 |176.0 |0.5 | |Ethanol |172.8 |172.5 |0.3 | |Propan-1-ol |178.7 |178.4 |0.3 |

Discussion:
Error was ignored in this experiment due to heat loss to the environment, and:

The specific heat capacity was 0.39. From this, molar heat of...
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