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Around how much do hot plate heat knobs increase per number?

  1. Jan 30, 2017 #1
    In my labs we use hot plates with a 0-10 temperature knob. The hot plates don't have a temperature monitor, so i have no idea how hot each number can increase it or how hot it is at the time. Sometimes i have labs where i have to heat something to more specific temperatures or else the reaction will change or it will boil over. My only option right now is to use a thermometer which isn't always practical, and still its easy to mess up.

    Is there a general rule with hot plates and the heat knob numbers? I know there might be factors like, room temperature. But i'm not doing anything that requires super precision, so i only really need a decent estimate. The only thing i know is the temperatures are 25°C at "1" and 550°C at "10"

    We use these http://www.sigmaaldrich.com/catalog/product/aldrich/cls6795220?lang=en&region=US

    Only thing i could think of is heating water and checking the temperature before heating anything important. But i wont have enough time for that. And my professor might say things like "watch it and don't let it boil too violently", but i just feel like theres just too much of a chance of messing up.
    Last edited: Jan 30, 2017
  2. jcsd
  3. Jan 30, 2017 #2
    The temperature of what is 25c at 1 ??? ... the temperature of the plate with nothing on it? ....or a small beaker of water ...or a large beaker of water????

    The temperature will vary depending what you have on the plate .... a big beaker of water will have a lower temperature because it has a larger surface area and dissipates the heat to the environment more effectively , a small beaker of water will get hotter , for a given setting.
  4. Jan 30, 2017 #3
    I'm not sure, i got it from the website. I'm assuming its the plate but i have no idea. And yeah the temperature would be different depending on the amount of what im heating, but i'm asking this for smaller amount substances, i should have specified that.
  5. Jan 30, 2017 #4
    I see that now from the website "25-550 °C temp. range" ...I would imagine 25c (room temp) is setting zero .... there's no way you can know the temp...every item you put on the plate has different heat transfer properties , only through experience .... as the prof says "watch it"
  6. Jan 30, 2017 #5


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    Staff: Mentor

    The only way of being sure is to use a thermometer so no maker will give other scale than the power on the plate (which is what these 0..10 marks on the knob really are).

    When you are working in a repeatable settings (air-conditioned room with a constant temperature, always the same sample/vessel size) you can prepare your own table of what settings to use. Even then occasionally checking if the temperature is what you think it is won't hurt.
  7. Feb 1, 2017 #6
    You really just need to know your hotplate. IIRC, the scale is logarithmic, not linear.
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