- #1
Fly_High
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Why the mercury in glass-laboratory thermometer doesn't stick to glass?
Mercury in glass-laboratory thermometer doesn't stick to glass?
- Thread starter Fly_High
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- Glass Mercury Thermometer
In summary: Also, glass is a highly polar material while mercury is not, so there is also a lack of attraction between the two substances. In summary, the low viscosity and nonpolar nature of mercury contribute to its inability to stick to glass in a laboratory thermometer.
- #2
daysyworld
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Hi, the reason is that the viscosity of Mercury is low 0.159*10^-2 (kg/ms).
(for water = 0.105*10^-2 (kg/ms))
You can view more intuitively if you know for example the Glicerine viscosity
(139.3 * 10^-2 ( kg/ms), three order of magnitude higher)
(for water = 0.105*10^-2 (kg/ms))
You can view more intuitively if you know for example the Glicerine viscosity
(139.3 * 10^-2 ( kg/ms), three order of magnitude higher)
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- #3
Cesium
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Viscosity more has to do with how much the molecules of a liquid "stick" to each other and not to another substance like glass. Mercury doesn't adhere to glass well because it's nonpolar while glass is polar.
- #4
daysyworld
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Cesium said:
I'm not agree whit your opinion. Water is polar and it doesn't andhere to glass.
"[URL
" Viscosity is a measure of the resistance of a fluid to deform under shear stress. It is commonly perceived as "thickness", or resistance to flow."[/URL]
Because this resistance, the fluid who have high viscosity take more time to return to inicial position, in this case, to the bottom of termometer ( for the gravity strength).
Cheers.
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- #5
pixel01
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Fly_High said:
There are two reasons : first mecury has very high surface tension, i can't remember but probably about 4 or 5 times higher than that of water. It is so strong that any adhesion force can not compete with. According to my experience, Hg does not stick to any material except for the case it react to become an amalgam. Secondly, water is polar and so is glass. If water does not stick to glass, probably be the glass surface is not clean.
- #6
Cesium
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When you pour water out of a glass container, does all the water flow out? Nope, some stays stuck against the walls of the container!
Some info about thermometers: http://home.earthlink.net/~dmocarski/chapters/chapter6/main.htm
And from that page "Another reason is that water sticks to glass and mercury and alcohol don't."
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- #7
C1ay
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Yeah, I know it's an old thread but it popped up when I was googling the viscosity of mercury and thought I would post a useful answer regarding the OP for others that end up here the same way I did.
Anyhow, high cohesion is the reason mercury doesn't wet the glass. Mercury molecules are attracted to each other more than the glass. That is why the meniscus of mercury in a glass container is convex.
Water on the other hand has a low amount of cohesion and it is attracted to the glass more than itself. That's why the meniscus of water is concave. Relative to glass, the adhesive force of the water is higher than it's cohesive force. Place it on a hydrophobic surface, like a waxed car, and it will behave as mercury does with glass and bead up from it's own cohesive force.
- #8
lightarrow
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Because Hg-Hg bonds in the liquid metal are much stronger than Hg-glass bonds, so mercury prefers to stay...with itself (it's an introvertedFly_High said:
)1. Why does the mercury in a glass laboratory thermometer not stick to the glass?
Mercury is a liquid metal with very low surface tension, meaning it does not easily stick to other surfaces. In addition, the glass used in laboratory thermometers is specifically designed to have a smooth surface that minimizes friction, allowing the mercury to easily slide up and down the thermometer.
2. Is it normal for a glass thermometer to have a gap between the mercury and the glass?
Yes, it is normal for there to be a small gap between the mercury and the glass in a laboratory thermometer. This is due to the expansion and contraction of the mercury with changes in temperature, causing it to pull away from the glass slightly.
3. Can the mercury in a glass thermometer ever stick to the glass?
In rare cases, the mercury in a glass thermometer may appear to be stuck to the glass. This is usually due to a buildup of dirt or residue on the inside of the glass, preventing the mercury from freely moving. Cleaning the thermometer with a gentle soap and water solution should solve this issue.
4. What is the purpose of the mercury in a glass laboratory thermometer?
The mercury serves as the measuring element in a glass laboratory thermometer. As it expands or contracts with changes in temperature, it moves up or down the thermometer, providing a precise measurement of the temperature.
5. Can a glass thermometer be used for both hot and cold temperatures?
Yes, a glass thermometer can be used for both hot and cold temperatures. However, it is important to note that extreme temperatures (above 500°C or below -38°C) can cause the glass to crack or the mercury to evaporate, rendering the thermometer unusable.
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