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Why is water boiling at 96?

  1. Nov 27, 2012 #1
    I have tested this with 3 thermometers, 2 Taylor digitals and a candy thermometer...

    My water boils at 96 celcius and I'm in Pattaya Thailand with sea elevation of 8 meters...

    Actually slow boil at 93-94 and very heavy boil at 97-97

    I'm perplexed...!
     
  2. jcsd
  3. Nov 27, 2012 #2

    AGNuke

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    Probably due to reduced atmospheric pressure.
     
  4. Nov 27, 2012 #3
    Thanks

    But if I am at sea level?

    Pressure is 1010 millibar, nothing spectacular...

    Is it normal for boiling temperatures to vary as much as 5 Celsius at see level?
     
  5. Nov 27, 2012 #4

    chemisttree

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    Are you doing this in a lab with ventilation hoods?
     
  6. Nov 27, 2012 #5
    No ventilation hoods, just in large pot, 60 liters with 50 000 btu gaz burner, I also tried a 2 liter pot in case of limited heat distribution, same result.

    Thermometers are Taylor instruments:

    1479 5* Commercial Wireless Remote Thermometer

    Plus a standard glass candy thermometer, they all agree on the readings.

    I am boiling tap water, maybe I'll try distilled or ionized to see if it makes a difference?
     
  7. Nov 27, 2012 #6

    chemisttree

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    Try using a good lab grade thermometer with an immersion depth line. Insert the good thermometer up to the immersion depth line. If it has no line you must submerge the whole thing. Candy thermometers are not very precise and I think you've just proven that a barbeque thermometer cannot be used for precise work even though the digital readout gives you a temperature to a precision of tenths of a degree..
     
  8. Nov 27, 2012 #7
    Hi Chemistree,

    I am getting an HM Digital pH meter tomorrow, so that will be the fourth instrument confirming my readings...could they ALL be defective simultaneously?

    But I agree with you, I need something more accurate, however...I'm in Thailand...where can I find a proper thermometer online and what is the ball park I should expect to pay?
     
  9. Nov 27, 2012 #8

    chemisttree

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    I don't know how much a red liquid (don't use mercury) thermometer costs in Thailand. These guys might.

    Don't measure boiling water with a pH meter... PLEASE!
     
  10. Nov 28, 2012 #9

    Hurkyl

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    This was my first thought; I would expect minerals and such in the water to affect the boiling point. Although, I'm not sure which way it should affect it.
     
  11. Nov 28, 2012 #10

    DrDu

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    Why not? For precision glass thermometers in laboratories mercury is still the gold standard.
    The digital food thermometer has just ridiculously bad precision.
    You need a calibrated precision thermometer e.g.
    http://www.greisinger.de/index.php?task=2&wg=26
    And should closely follow the instructions.

    Further points to consider:
    I would not use such a large volume. Is the vapour in equilibrium with the liquid (i.e. you should measure not in an open pot but in a closed system with only a small opening for pressure equilibration. ) ?
    Purity of the water?
    Even with a glass thermometer there are correction factors for temperature of the surrounding and the like.
     
  12. Nov 28, 2012 #11
    I have tried reducing the volume to 1 liter, the probe is fully submerged with the sensor not touching the steam. Will do a test with a closed container and ionized water later today or tomorrow and record the results.

    All 3 thermometers record the exact same temperatures in unison...one of them is glass with red liquid.

    If I can't figure this out I'll do a movie on youtube of the experiment, I'd really like to get to the bottom of this!
     
  13. Nov 28, 2012 #12

    Borek

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    Up. It is called "boiling point elevation" for a reason.
     
  14. Nov 28, 2012 #13

    russ_watters

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    I think you just calibrated your thermometers....

    Now try them in ice water....
     
  15. Nov 28, 2012 #14
    Ice water test is next with all 3
     
  16. Nov 28, 2012 #15
    Actually, something else I will do is try the thermometer in one of the local noodle soup shops pots in the street (I'm in Thailand ;) and see what boiling temperature I get with them!
     
  17. Nov 28, 2012 #16
    There may be something wrong with your thermometer. Try another thermometer.

    If you used a massive thermometer, then maybe you didn't wait for the thermometer to equilibrate. What type of thermometer did you use?


    Okay. After this, one has to consider the more exotic explanations. Maybe the water is not boiling.

    1) Maybe the water is effervescing.

    The solubility of gases decreases with temperature. If the water had a lot of air dissolved in it, then the air would be driven out of the water forming bubbles.

    If the water had just been taken out of a cold area, the water could have dissolved a lot of air. When you heated it, the air could have been driven out the air.

    If this is effervescing, then the bubbles should soon stop.

    2) Maybe the water is mixed with a more volatile liquid such as alcohol.

    Also, the water may be mixed with a more volatile liquid such as alcohol. A water-alcohol mix would have a lower boiling temperature than neat water. If you keep boiling a water-alcohol mixture, the boiling temperature will rise as the alcohol is driven off.

    3) Maybe the liquid isn't water at all !-)

    No suggestions there.
     
  18. Nov 28, 2012 #17

    chemisttree

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    The only things I can think of that would lower the BP would be some azeotrope or if the work were being conducted in a lab under slightly negative pressure, thus my question about ventilation hoods.

    If this work is being done indoors, open a door to the outside a small amount and see if you feel an inward draft of outside air. Alternatively, you could accurately measure the atmospheric pressure where the work is being conducted. The boiling point of water is affected by pressure so that a BP reading of 96C for water occurs at about .87 bar which is equivalent to an increase in elevation of about 3200 feet.
     
  19. Nov 28, 2012 #18

    chemisttree

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    You shouldn't find mercury thermometers in a food grade manufacturing facility. The manufacturing facility I'm familiar with has specific instructions against having them on the property.

    Probably better to say it has ridiculously bad accuracy. It could indeed measure temperature with an acceptable precision but just not accurately.
     
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