"Heat of Combustion of Ethanol" Prac (1 Viewer)

[~ ReNcH ~]

Does anyone have a copy of the procedure etc. for the Heat of Combustion of Ethanol prac? I have a prac exam no it so I just want to read over it first.

 

[archangel leila]

Don't have a formal procedure on hand, but basically (cliff's notes version):
1. Set up retort stand, boss head + clamp
2. Weigh spirit burner containing alcohol + record mass
3. Clamp flask/beaker containing mass of water (that you've recorded) over spirit burner just above wick and measure initial temp
4. Light wick and let burn (flame should be just touching bottom) till water's temp rises a certain no. of degrees + record
5. Extinguish flame + weigh final mass of spirit burner (initial mass - final = mass of alcohol burned)

6. Use equation: change in heat = m (of water) x C (specific heat of water) x change in temp (giving energy change in alcohol for that amount of alcohol)
7. To find molar heat of combustion, divide the energy value you just calculated by the no. of moles burned (use mass/Molar mass to find no. of moles)

Safety: Alcohol away from flame, bottles have lids on, avoid breathing in, wear glasses

Improve: use draught shield to stop heat loss, repeat, more accurate thermometer

I just did that prac test, still waiting for marks so not sure if this procedure pays off, haha. Hope it helps. Roger that.

 

[~ ReNcH ~]

Ok, cool. Thanks.
Is it an easy prac? - I generally hate pracs...

 

[MedNez]

Yeah, we did it as just part of our syllabus work. Was just another experiment, not very difficult, and took less than a period to do.

 

[~*HSC 4 life*~]

common trial exam question

learn some diagrams too
stoichiometric calculations are always the same (unless different peices of info are given then sometimes u need to work backwards)
oh and also learn some reasons why the value calculated may not be the same as the one found in an SI data book
they usually are
- heat loss to surroundings
-parralax error (in reading thermometer)
- and incomplete combustion

 

[jamesy_1988]

Does anyone have a copy of the procedure etc. for the Heat of Combustion of Ethanol prac? I have a prac exam no it so I just want to read over it first.

you can have a look at my experiment at www.geocities.com/jamesyscience_chemistry/pmexp/1.5.doc

You will always get really large error percentages because of the amount of heat lost to the surrounding environment.

I would really appreciate you feed back on my site

You can email me at jamesy_1988@hotmail.com

Also my site is for physics and biology if you need help. The main address of the page is www.geocities.com/jamesyscience

Jamesy

 

[TimeAndTide]

How the hell can you work out an error percentage in these? The sources probably used a differnt appartus and method than yours.

 

[Templar]

How the hell can you work out an error percentage in these? The sources probably used a differnt appartus and method than yours.

Different apparatus, yes. Different method, not really. The fuel is still burnt to heat water, and change in temperature measured.

It doesn't really matter. Error percentage is still there.

 

[TimeAndTide]

Ermm...WRONG!, the method is not the same, since they may have heated it longer than you, and they may have had ideal lab conditions (Pressure, no draft).

so you're wrong. Eat my crap.

 

[Xayma]

- heat loss to surroundings
-parralax error (in reading thermometer)
- and incomplete combustion

You also have that it isn't pure ethanol. Since it is way too expensive for schools to acquire if they have to keep doing it. Alot cheaper just to use a 95% ethanol solution.

 

[taxman]

You also have that it isn't pure ethanol. Since it is way too expensive for schools to acquire if they have to keep doing it. Alot cheaper just to use a 95% ethanol solution.

Not to mention illegal to have 100% alcohol. Unless there are exclusions for schools, I'm not sure. My pop got fined for making grapa in his garage which apparently is also illegal.

As for Time and Tide, the heating for periods of time shouldn't make a difference, as the calculations you use allow for this, with change in temperature and the amount of fuel lost, meaning heating time shouldn't make a difference. The main factors influencing differences in data will still be lost heat, incomplete combustion and instrument/human error.

 

[Slidey]

We did this prac at my school. The teacher got called on his mobile and then everybody got sick of it and put all their ethanol/butanol/propanol together to form a big fire. The ceilling was scorched and when he came back they couldn't put it out, so he sat their grinning at their stupidity as they did things like whack it with books to put it out. In the end they put it out... haha.

 

[taxman]

We did this prac at my school. The teacher got called on his mobile and then everybody got sick of it and put all their ethanol/butanol/propanol together to form a big fire. The ceilling was scorched and when he came back they couldn't put it out, so he sat their grinning at their stupidity as they did things like whack it with books to put it out. In the end they put it out... haha.

Hahahaha...classic! Our old teacher used to get bored teaching us stuff, so he let us set up a bunsen burner and blow corn flour over it, making this mad flame thrower thingy. Fire...mheh heh mheh.

 

[Slidey]

Yea, my teacher's awesome. He's lax enough to be "cool", strict enough to make us work, and good enough to teach us well.

 

[PyRo999]

Our Teacher is a fucken moron, hooked up a rubber house and a glass pipe to the gas tap, was a kool flamethower untill he sat the pipe down to turn if off, at least he couldn't give us the sheets we were supposed to do anymore...