Why the alcohol thermometer is less precise than the mercury one?

In summary, ORFI thinks that the alcohol thermometer is less precise because the thermal expansion coefficient of alcohol is not constant. Additionally, the error sources would be the meniscus and linearity of the equation.
  • #1
ORF
170
18
Hi,

Why the alcohol thermometer is less precise than the mercury one?

If I remember correctly, it is because the thermal expansion coefficient of alcohol is not constant, but I am not sure.

Thank you for your time.

Regards,
ORF
 
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  • #2
I think it's because alcohol wets the walls of the thermometer making the reading less accurate.
 
  • #3
My first thought was coefficient of expansion; maybe mercury is higher so a bigger change in volume per change in temperature. But this is wrong. A little internet searching shows volumetric coefficients for "ethyl alcohol" as 1100 (x10-6 per degree C), compared to 180 for mercury. So the alcohol expands ~6 times as much.
 
  • #4
ORF said:
Why the alcohol thermometer is less precise than the mercury one?
Do you know for sure that it is? I thought the reason mercury is used is because it allows for reasonable sized thermometers whereas alcohol ones would be awkwardly large to get an error range similar to a mercury one.
 
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  • #5
kuruman said:
I think it's because alcohol wets the walls of the thermometer making the reading less accurate.
Do you mean that the meniscus is variable, or that it's more prone to humans misreading it consistently?
 
  • #6
Mostly the meniscus.
 
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  • #7
Since both have to be read by a human (I assume), then I'm not sure your accuracy question is complete. You are not addressing the biggest error source, IMO. This is one of many reasons everyone uses electronics to collect data these days.

Anyway, why would there not be a deterministic equation that relates temperature to liquid volume in a sealed glass tube? Granted, it might not be linear, but does that matter?

A question for those who know materials science better than I (a pretty low bar, actually). What can you do to change the volume of a liquid at a fixed thermal equilibrium and constant pressure (because the glass is thick)? Those would be the error sources, right?
 

Related to Why the alcohol thermometer is less precise than the mercury one?

1. Why is alcohol used in thermometers instead of mercury?

Alcohol is used in thermometers because it has a lower freezing point and boiling point compared to mercury, making it suitable for measuring a wider range of temperatures. Additionally, alcohol is less toxic and less expensive than mercury, making it a safer and more cost-effective option for thermometers.

2. How does the precision of an alcohol thermometer compare to a mercury thermometer?

The precision of an alcohol thermometer is typically less than that of a mercury thermometer. This is because alcohol has a higher coefficient of expansion, meaning it expands and contracts more with changes in temperature, resulting in a larger margin of error.

3. Can alcohol thermometers be used for accurate temperature measurements?

Yes, alcohol thermometers can be used for accurate temperature measurements within a certain range. However, they are not as precise as mercury thermometers and may not be suitable for scientific or medical applications where precise measurements are required.

4. What factors can affect the precision of an alcohol thermometer?

The precision of an alcohol thermometer can be affected by factors such as the quality and purity of the alcohol used, the material and construction of the thermometer, and external factors such as air pressure and humidity. These factors can cause slight variations in the expansion and contraction of the alcohol, leading to less precise temperature readings.

5. Is it safe to use an alcohol thermometer?

Yes, it is generally safe to use an alcohol thermometer. However, it is important to handle them with care as they contain flammable liquid. In case of accidental breakage, the alcohol should be cleaned up immediately to prevent any potential hazards. It is also important to note that alcohol thermometers should not be used for measuring high temperatures, as the alcohol can evaporate and cause the thermometer to break.

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