EXPERIMENT
AIM: To determine the experimental heat of combustion of methanol (CH3OH) and ethanol (CH3CH2OH).
To decide which would be a better choice to take on a camping trip.
MATERIALS: 1 copper container 1 Clamp
1 Spirit Lamp with Wick Ethanol
1 Retort Stand Methanol
1 Box of Matches Water
1 Electronic Balance Thermometer
PROCEDURE:
Firstly, Measure the weight of the empty Copper container on the electronic balance. Record your results in a table.
Secondly, fill the copper container with 100ml of water.
Thirdly, Attach the copper container to the clamp which is them attached to the retort stand.
Fourthly, Measure the weight of the spirit burner containing known amount of Methanol (CH3OH).
Fifthly, Measure the initial temperature of the water with the thermometer. Then light the spirit lamp’s wick and place it under the copper container.
Sixthly, stir the water using the thermometer and constantly check the temperature. Once the temperature is 10oC greater than the initial temperature, extinguish the spirit burner.
Seventhly, reweigh the mass of the spirit burner.
Eighthly, Repeat steps 1 through to 7 for ethanol (CH3CH2OH).
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The combustion of Methanol and Ethanol can be represented through:
Methanol: 2CH3OH(l) + 3O2(g) 2CO2(g) + 4H2O(l)
2(358+463+(414×3)) + (498×3) (804x2x2) + (463x2x4)
5620 6920
6920-5620= 1300
1300/2= -650 KJ/mole
Ethanol: CH3CH2OH(l) + 3O2(g) 3H2O(l) + 2CO2(g)
346+358+463+ (414×5) + (498×3) (804x2x2) + (463x2x3)
4731 5994
5994-4731= -1263 KJ/mole
Note: Combustion values are not exact to the book due to different values of bond energies.
Risk Assessment
Methanol: Inhalation and ingestion may be fatal. Inhalation also causes low blood pressure, headache, nausea, vomiting, dizziness, narcosis, central nervous system depression and suffocation. May irritate skin and eyes and temporarily damage corneas. Ingestion may cause blindness, vomiting, headaches and dizziness.
Ethanol: Ingestion may be fatal. May be absorbed through the skin. Vapor and mist irritates the eyes, mucous membranes and upper respiratory tract. May cause eye damage, nausea, dizziness, headache and central nervous system depression.
Methanol has a flash point of 12oC and ethanol 13oC. Methanol and ethanol’s ignition temperatures are 455oC and 363oC respectively.
Solvents and other flammable liquids should be used with constant regard to the danger they pose to life. They should be stored in non-flammable containers, with a child safety lid to prevent indigestion. Carrying excess of 50L of methanol or ethanol is hazardous because if ignited it could be fatal. Do not store the fuel in the spirit burner, fuel could leak out through the wick.
Combustion of Methanol
Data Trial 1
initial mass of burner (g)
final mass of burner (g)
initial temperature of water (C°)
final temperature of water (C°)
Calculations Trial 1
mass of methanol burned(g)
temperature change of the water (C°)
(final temperature-initial temperature)
specific heat capacity of water 4.18 J K-1 g-1
Specific heat capacity of copper 0.387 J K-1 g-1
Heat released by the Methanol burnt=heat gained by copper container + heat gained by water= -(mCcopper calorimeter) +mCT(water))
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M(CH3OH) 32.042g mol -1
Convert to molar heat of combustion
-Heat released X 32.042g/mass of Methanol burned
Combustion of Ethanol
Data Trial 1
initial mass of burner (g)
final mass of burner (g)
initial temperature of water (C°)
final temperature of water (C°)
Calculations Trial 1
mass of methanol burned(g)
temperature change of the water (C°)
(final temperature-initial temperature)
Specific heat capacity of water 4.18 J K-1 g-1
Specific heat capacity of copper 0.387 J K-1 g-1
Heat released by the Ethanol burnt=heat gained by copper container + heat gained by water= -(mCcopper calorimeter) +mCT(water))
M(CH3CH2OH) 46.1g mol -1
Convert to molar heat of combustion
-Heat released X 46.1g/mass of ethanol burned
Discussion and Conclusion.
The experimental results are much lower due to some experimental errors. Some factors may include loss of heat from copper container heating up (large error) and to help prevent losing heat you could use insulation, electronic balance readings not accurate enough (small error), accuracy of reading the temperature on the thermometer at eye level (small error).
Incomplete combustion of reactants, leading to the formation of soot and carbon monoxide. The specific heat capacity of glass and copper is 0.84 J K-1 g-1 and 0.387 J K-1 g-1 respectively. Therefore since glass has a higher specific heat capacity than copper, glass would take more energy to heat up and hold heat in for longer. Rather than using a copper container and loosing heat it would be better to use a glass beaker.
The validity and reliability of the results would not be very valid/reliable. The major factor contributing to this would be measuring our results because getting it to a near or exact result as in the textbook would practically be impossible with the equipment provided and under our conditions. The electronic balance which was provided was only to of 2 decimal places. Some mass would also be lost due to reading the meniscus at eye level.
Through thorough experiments it would be more efficient to use ethanol because, the heat of combustion of ethanol is 1367 KJ/mole, ignition temperature of 363oC and flash point of 13 oC. Whereas Methanol’s heat of combustion is 724 KJ/mole, ignition temperature of 455oC and flash point of 12 oC.
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Since ethanol has a higher heat of combustion you would need to use 3 times the amount of methanol to get the same amount of energy produced from ethanol. Although ethanol has a lower ignition temperature then methanol, it is still relatively high in a sense that it wouldn’t ignite unless the temperature reached 363oC. Both methanol and ethanol have low flash points below room temperature. They both are potentially dangerous because a spark or flame can result in a fire or explosion. Ethanol possesses a flash point higher than methanol by 1oC. If choosing a fuel in relation to their flash points it wouldn’t really be major concern since there is only a minute difference.
Ethanol is also much safer if consumed because ethanol in the form of alcoholic beverages has been consumed by humans since pre-historic times. Consumption of ethanol in small quantities may be harmless or even beneficial, larger doses result in drunkenness or intoxication and, depending on the dose and regularity of use, can cause acute respiratory failure or death and with chronic use has medical repercussions.
Methanol on the other hand when metabolized produces toxic substances. Methanol is oxidized by alcohol dehydrogenase enzymes in the liver to the poisonous formaldehyde, which can cause blindness or death. An effective treatment to prevent formaldehyde toxicity after methanol ingestion is to administer ethanol. Alcohol dehydrogenase has a higher affinity for ethanol, thus preventing methanol from binding and acting as a substrate. Any remaining methanol will then have time to be excreted through the kidneys. Remaining formaldehyde will be converted to formic acid and excreted.
Therefore through experimental results and detailed risk assessment ethanol would be a better choice to take on an overnight camping trip. Empty containers retain product residue, (liquid and/or vapor), and can be dangerous. Ethanol should be stored in a tightly closed child proof container. Do not pressurize, cut, weld, braze, solder, drill, grind, or expose empty containers to heat, sparks or open flames. Keep away from sources of ignition and store in a cool, dry, well-ventilated area.
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