References for background information: applied science book, handouts and website:
Risk assessment:
= highly flammable. Ref:
= irritant. Ref:
= toxic. Ref:
= harmful. Ref:
Apparatus list:
- Spirit burner – it is used to burn alcohols in a safe way.
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- Copper can – avoid burning the hand while holding it as it cools down quickly.
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- Clamp and stand - clamp and stand is used to hold the copper can while heating up the water.
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- Electronic balance (to 2 d.p.) – it is used to weight the alcohols to find out their masses.
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- Goggles – it is used to prevent any chemicals in contact with the eyes.
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- Mercury thermometer – it is used to record the temperature of the water when the water is heating up.
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- Tap water – it is used to heat up in the copper can.
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- Methanol – it is one of the five alcohols used to compare the enthalpy change of combustion.
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- Porpan-1-ol - it is one of the five alcohols used to compare the enthalpy change of combustion.
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- Ethanol - it is one of the five alcohols used to compare the enthalpy change of combustion.
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- Butan-1-ol - it is one of the five alcohols used to compare the enthalpy change of combustion.
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- Propan-2-ol - - it is one of the five alcohols used to compare the enthalpy change of combustion.
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Method:
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200cm3 was filled in the copper can which is also known as the calorimeter
- The copper can was placed on the clamp and stand
- The mercury thermometer was placed into the copper can to record the original temperature of the water.
- After recording the temperature, the mass of the alcohols were measured using the electronic balance and the results were in 2 decimal places.
- Then, the spirit burner was place under the copper can which were used to burn.
- A suitable draft exclusion system was arranged to reduce heat loss.
- The wick was lighted to heat the water.
- While heating the water, the thermometer was used to stir the water to get an accurate temperature of the water.
- The mercury thermometer was being observed till the temperature was risen by 15°C to 20°C.
- As soon as the temperature was risen by 15°C to 20°C, the spirit burner’s lid was placed on the flames to extinguish the burner.
- When the temperature reached its highest point, the temperature was recorded.
- The mass of the alcohol was placed on the electronic balance to record the final mass.
- The experiment was repeated in the same way for the five alcohols
- At the end of the experiment, all the results was recorded on a suitable table
Results:
Comparison:
Calculations:
Q = m x c x ΔT
Q= heat exchanged with the surroundings (J)
m= mass of water (g)
c= specific heat capacity of water (4.18 Jg-1K-1)
ΔT = temperature change (°C)
Butan-1-ol:
Q = m x c x ΔT
= 200 x 4.18 x 15
= 12540J
12540/ 1000 = 12.54 KJ
ΔH°C = Q / mole
= 12.54/9.594594595x10-3
= 1307 kJmol-1
Propan-2-ol:
Q = m x c x ΔT
= 200 x 4.18 x 19
= 15884J
15884/ 1000 = 15.884 KJ
ΔH°C = Q / mole
= 15.884/0.019
= 836 kJmol-1
Methanol:
Q = m x c x ΔT
= 200 x 4.18 x 16
= 13376J
13376/ 1000 = 13.376 KJ
ΔH°C = Q / mole
= 13.376/0.0484
= 276 kJmol-1
Propan-1-ol:
Q = m x c x ΔT
= 200 x 4.18 x 15
= 12540J
12540/ 1000 = 12.54 KJ
ΔH°C = Q / mole
= 12.54/0.012
= 1045 kJmol-1
Ethanol:
Q = m x c x ΔT
Q = 200 x 4.18 x 15
= 12540J
12540/ 1000 = 12.54 KJ
ΔH°C = Q / mole
= 12.54 / 0.273
= 45.9 kJmol-1
Enthalpy changes:
Graph:
- Ethanol
- Methanol
- Propan-2-ol
- Propan-1-ol
- Butan-1-ol
Analysis:
Comparing fuels:
To find out the best fuel, compare the fuels by measuring the mass of fuel burned in the experiment. The best fuel will release the most energy per gram of fuel. The calculation for the energy released:
Energy released (J/g of fuel) = energy transferred to water (J) ÷ mass of fuel burned (g)
Ethanol:
Energy released (J/g of fuel) = energy transferred to water (J) ÷ mass of fuel burned (g)
= 12540/ 0.72
= 17417 J/g of fuel
Methanol:
Energy released (J/g of fuel) = energy transferred to water (J) ÷ mass of fuel burned (g)
= 13376J/ 1.55g
= 8630 J/g of fuel
Propan-1-ol:
Energy released (J/g of fuel) = energy transferred to water (J) ÷ mass of fuel burned (g)
= 12540/ 1.14
= 14581 J/g of fuel
Propan-2-ol:
Energy released (J/g of fuel) = energy transferred to water (J) ÷ mass of fuel burned (g)
= 15884/ 1.14
= 13933 J/g of fuel
Butan-1-ol:
Energy released (J/g of fuel) = energy transferred to water (J) ÷ mass of fuel burned (g)
= 12540/ 0.71
= 17662 J/g of fuel
Conclusion:
According to my calculation, the best fuel that released a lot of fuel was butan-1-ol and ethanol. Methanol released the least fuel out of the five alcohols. Endothermic is when energy absorbed more than energy released whereas exothermic is when energy released is more than the energy absorbed. According to my table, methanol and propan-2-ol are endothermic. Ethanol, propan-1-ol and butan-1-ol are exothermic. It also shows that ethanol has released a big amount of energy compared to the other five alcohols and methanol has released a small amount of energy.
Linking with my aim, I have investigated the difference in enthalpy of combustion for all the five different alcohols and found out the best fuel out of the five alcohols.
Evaluation:
Overall, my accuracy in this experiment was quite accurate. While analysing the results, all the units of the experiment were close and the average mass and temperature were almost right and accurate except one or two of them. There are two types of error which can be occurred in this experiment:
- Procedure error
- Measurement error
- Procedure error
Procedure error can occur in the procedure of the experiment, the errors are mainly while transferring solution, the volume of the solution can decrease which would not be accurate for the final record. Another one is the reaction time for extinguishing the flames when the temperature reached by 15°C to 20°C, as a rise on temperature makes a big difference in the result.
How to improve it?
The only way to improve the procedure error is to avoid transferring water in many beakers. In addition, extinguish the flames as soon as possible will receive an accurate temperature of the alcohols.
- Measurement error
Measurement error can occur while taking the reading from the measuring cylinder as the reading should be rounded up to the nearest ± 1 cm3, the thermometer should be ±0.5°C and the weighting scale should be rounded up to ±0.005g. This can be accurate most of the time in experiment but sometime it can’t be completely accurate. Another measurement error can occur if the person only does the experiment once.
How to improve it?
The best way to improve it is to try to be more accurate rather than rounding up to the nearest numbers sometimes and the experiment should be repeated twice or three times to be more accurate.