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

[AMan24]

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 won't 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 there's just too much of a chance of messing up.

 

[oz93666]

The only thing i know is the temperatures are 25°C at "1" and 550°C at "10"
.

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.

 

[AMan24]

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.

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 I am heating, but I'm asking this for smaller amount substances, i should have specified that.

 

[oz93666]

I'm not sure, i got it from the website. I'm assuming its the plate but i have no idea

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"

 

[Borek]

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 I am heating, but I'm asking this for smaller amount substances, i should have specified that.

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.

 

[Kevin McHugh]

You really just need to know your hotplate. IIRC, the scale is logarithmic, not linear.