I have just been given a prac request for Heats of Combustion. This is a design your own prac for Year 12 students, and the prac says "You will be provided with burners containing the fuel" I guess that is my part!. Teacher has asked for fuels such as methanol, ethanol ,kerosene, paraffin, Octane??
Not having done this before in school, I have vague idea that we should use spirit burners or maybe even crucibles to heat the fuel. If so how would I recommend we go about this, I have found some dusty spirit burners at the very back of a cupboard. How do I use them, how full should they be etc. etc.
If anyone can help me with this I would be most grateful. I need to be knowledgeable before I let students (and teacher) start burning those flammable liquids!!
heat of combustion
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PhysicsOne
- Posts: 25
- Joined: 18 Jul 2006, 10:00
- State/Location: NSW
Re: heat of combustion
Our chemistry teacher has used different fuels in spirit burners. He hasn't told me about any problems.
The wick just needs to be moist for the liquid to travel up it so you don't have to fill them completely. What is left could be poured back into the bottle.
The wick just needs to be moist for the liquid to travel up it so you don't have to fill them completely. What is left could be poured back into the bottle.
Re: heat of combustion
Yes Pilar,
Go with the dusty spirit burners. It's useful to weigh the burners before & after to get the mass of the fuel burned, and heat a designated amount of water, e.g. 10 or 50mls. Get the before/after temps of the water. Then you will get a temp change and a mass of fuel burned, which combined with the specific heat of water will give you a joules per gram measurement.
Is that making sense?
Go with the dusty spirit burners. It's useful to weigh the burners before & after to get the mass of the fuel burned, and heat a designated amount of water, e.g. 10 or 50mls. Get the before/after temps of the water. Then you will get a temp change and a mass of fuel burned, which combined with the specific heat of water will give you a joules per gram measurement.
Is that making sense?
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RosalieM
- Posts: 1795
- Joined: 20 Mar 2007, 10:00
- Job Title: Lab Assistant
- Suburb: Tamworth
- State/Location: NSW
Re: heat of combustion
We use spirit burners too. There are 2 methods used by teachers here. One is to weigh the burner before starting, and boil a set amount of water (I think usually 50ml) in a 'billy can' made from a baby food tin. The kids time how long it takes to heat the water and re-weigh the burner to see how much fuel has been used.
The other method is fairly similar only they have a set time instead of letting it reach boiling point. Same deal - weigh the burner, measure the change in temperature (eg over 5 minutes) and re-weigh the burner. We use retort stands and clamps to hang the billy over and the clamp then holds the thermometer as well.
I usually try to have the spirit burners about half full and write their contents on in permanent marker (which washes off easily). I have bottles for 'spirit burner fuel' to pour any leftovers back into which only get used for this purpose. This way they don't get used for ester pracs or other things. I'm not very good at doing this though, and usually the burners just stay full of their fuel...
The other method is fairly similar only they have a set time instead of letting it reach boiling point. Same deal - weigh the burner, measure the change in temperature (eg over 5 minutes) and re-weigh the burner. We use retort stands and clamps to hang the billy over and the clamp then holds the thermometer as well.
I usually try to have the spirit burners about half full and write their contents on in permanent marker (which washes off easily). I have bottles for 'spirit burner fuel' to pour any leftovers back into which only get used for this purpose. This way they don't get used for ester pracs or other things. I'm not very good at doing this though, and usually the burners just stay full of their fuel...
Re: heat of combustion
Run with Smiley! 
although I would use about 50ml or 100ml of water in a beaker that I placed in a cardboard cylinder covered with Alfoil (that's a homemade Calirometer) and place on cutdown tripods or put spirit burner on an upturned beaker to raise height of flame to about 50 to 30 mm below bottom of beaker with water 
although I would use about 50ml or 100ml of water in a beaker that I placed in a cardboard cylinder covered with Alfoil (that's a homemade Calirometer) and place on cutdown tripods or put spirit burner on an upturned beaker to raise height of flame to about 50 to 30 mm below bottom of beaker with water 