mercury in glass-laboratory thermometer doesn't stick to glass?


by Fly_High
Tags: glass, glasslaboratory, mercury, stick, thermometer
daysyworld
daysyworld is offline
#2
Apr6-07, 03:45 PM
P: 12
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)
Cesium
Cesium is offline
#3
Apr7-07, 07:02 PM
P: 274
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.

daysyworld
daysyworld is offline
#4
Apr8-07, 02:55 AM
P: 12

mercury in glass-laboratory thermometer doesn't stick to glass?


Quote Quote by Cesium View Post
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.
I'm not agree whit your opinion. Water is polar and it doesn't andhere to glass.

" 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."

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.
pixel01
pixel01 is offline
#5
Apr8-07, 04:14 AM
P: 691
Quote Quote by Fly_High View Post
Why the mercury in glass-laboratory thermometer doesn't stick to glass?
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.
Cesium
Cesium is offline
#6
Apr8-07, 12:26 PM
P: 274
Water is polar and it doesn't andhere to glass.
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...pter6/main.htm

And from that page "Another reason is that water sticks to glass and mercury and alcohol don't."
C1ay
C1ay is offline
#7
Oct1-10, 01:46 PM
P: 16
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.
lightarrow
lightarrow is offline
#8
Oct13-10, 01:46 PM
P: 1,504
Quote Quote by Fly_High View Post
Why the mercury in glass-laboratory thermometer doesn't stick to glass?
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 introverted)


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