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Why might a bunsen burner heat slowly?

  1. Sep 10, 2012 #1
    I was heating water in lab and it took approximately 25 minutes to raise the temperature of my water by 65 degrees Celsius; perhaps the flame wasn't sufficient? I made certain that I could the the reducing and oxidizing flame, yet the liquid heated quite slowly. In addition, the flame was approximately 1/2-1 inch from the wire gauze supporting my beaker (ring stand apparatus). Perhaps there was not a sufficient supply of gas (i.e. gas flow valve not loosened properly)?

    Any ideas?
     
  2. jcsd
  3. Sep 10, 2012 #2

    Simon Bridge

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    "Slowly" compared with what?

    The rate of heating depends on how much heat is being supplied - which depends on the rate that the energy is available from the gas and the losses (bunsen flames are quite open so not all their heat goes into the water for eg. This is why gas stoves use lots of small flames in a ring instead of just one big one in the middle.)

    Raising the bunsen so the hot part of the flame touches the gauze will help.
    If you are describing a common lab setup, then it sounds like the gas supply is weak.
     
  4. Sep 10, 2012 #3
    Are bunsen burners normally used to boil water? Is there any reason not to use a hot plate?
     
  5. Sep 10, 2012 #4

    Simon Bridge

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    Yes, it is very common, in a school laboratory for eg., to use a bunsen to heat and boil water... and all kinds of other things besides.
     
  6. Sep 10, 2012 #5
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    When an experiment calls for boiling water (500 mL+) to be boiling, I use a hot plate. Some profs do not mind letting their students waste 25 minutes waiting for water to boil. I agree with your trouble shooting for the bunsen burner flame proximity issue.
     
  7. Sep 11, 2012 #6

    Simon Bridge

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    500ml is a lot of water - I've seldom seen more than 100mL in a teaching laboratory... especially since Occupational Health and Safety types had a look-see. 250-300ml would be max. Boiling water is the most dangerous substance we handle (by number and severity of injuries that is).

    I did campaign for and get a class set of hot-plates for the junior (college) labs ... mostly the burners are used because they are there. At secondary level - there are so many other things to spend the money on.

    OTOH: having to work with old and faulty equipment is a deliberate ploy to force students to think their way through problems (and write down what they actually did and not what their manuals say they should do). If it's too easy you don't learn. Whenever I'm in charge of a well-equipped teaching lab I sabotage it.

    Kiwis tend to have a "so what if we don't have all the right tools" attitude:
    http://www.stuff.co.nz/world/middle-east/5268312/NZ-crew-tows-US-helicopter-to-safety
     
  8. Sep 11, 2012 #7
    I'm an undergraduate and my school has quite a small chemistry department and lacks the resources of many other schools (i.e. we have less than "ideal" equipment). Are you saying that a hot plate would supply a more even and efficient heat (i.e. less heat dissipating into the environment)?

    At the moment, I do not require rapid heating of large volumes of water (500 mL+) but if I'm forced to use an older bunsen burner, I want to troubleshoot. Are you saying that I should move the flame closer to my wire gauze to aid in heating?
     
  9. Sep 11, 2012 #8

    Simon Bridge

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    Yes - a small hot-plate, or a camping-style gas burner, will be more efficient at heating stuff.

    That is exactly correct - open the holes so the flame makes a roaring noise. The tip of the blue part of the flame is the hottest bit. You want to position that bit just under the gauze.
    The gauze should glow red-orange.
    If you run the bunsen off fitted gas-taps, you can try adjusting the tap to maximize the flow (also check the nozzle for debris).

    If you are using the tripod setup I'm thinking of, you cannot adjust the tripod. So you'll need to put the bunsen on something. Preferably something stable that doesn't burn easy.

    This is the sort of learning you'd never get if the equipment was up-to-date and worked properly ;)
     
  10. Sep 11, 2012 #9
    1) Yes. I have received better results boiling water with a hot plate dan rather a bunsen burner.

    2) Good troubleshooting skills come from playing with the equipment at an early age. Call it work if you want, but I love this hands on stuff. Either way, have you tried to adjust the flame by altering the air flow on the burner unit?

    3) Yes you should move the flame closer. I'd put that bad boy right on the wire and let the flame's surface area increase.

    The only problem with this is most students don't realize that they have the freedom to go beyond what the lab manual says. This is why understanding the experiment and rewriting the stepwise procedure is crucial.

    Side note: Today is my physics day. WEEE!
     
  11. Sep 11, 2012 #10

    Simon Bridge

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    Which is why it is crucial for the teacher to spell out this freedom early.

    Part of introductory work involves exercises like giving stepwise instructions in the wrong order - the student's first task is to sort them out ;)

    My biggest problem is usually keeping the students close enough to the curriculum to pass the exams.

    biochem850 now gets to find out about the soot you get from too much spread in the flame, how the blue flame can melt a hole in the beaker if it boils dry, how there's no heat to speak of inside the blue cone, and to be careful washing up afterwards ... lots of fun.
     
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