Bubbles in a glass of water?

i think the bubble is produced by the air that contained in the water.just like soda water.

vaporisation?

DUE TO DENSITY DIFFERENCE, AIR WILL TAKE TIME TO COME OUT OF WATER.

MORE THE DIFFERENCE , MORE WILL BE TIME TAKEN BY AIR TO COME OUT

All tap water (and other water) has air disolved in it... in the mains supply maybe the ressure keeps the air disolved, when the water is left at ambient pressure and temperature some of the the air will precipitate out of solution. Well that's my view of it anyway!

John.

Mains water pressure should be a large part of it. The water possibly warms up when you have it standing around, which would reduce the solubility of the gases. (I think that electroman already implied this)

Dissolved CO2. If you measure the PH you will find it has lowered, become more acidic, as well.

CO2 makes the water acidic. So expelling it should make the water less acidic (unless changes in polarisability due to the temperature rise are more significant. This would initially be surprising - perhaps a chemist could confirm the situation?)

Perhaps it has something to do with cavitation?

As you fill up the glass bubbles form in the water due to its movements in the glass, which reduce the local pressure to below the vapor pressure of the water. Then the surface tension around the perimeter of the bubble holds it in place. That would mean the bubbles are not air, but H₂0 in its gaseous form.

This could explain why these bubbles are usually only found on the sides of the glass (the water pressure which would bring the bubble back into its liquid form is only being exerted on a half-sphere).

It could also explain why these bubbles behave differently from soda bubbles, which are dissolved CO₂ coming out of solution. The soda bubbles will dissapear after the soda has "gone flat" meaning all the CO₂ has come out of solution. The bubbles in the water will remain there almost indefinitely, as you have observed.

I could be wrong though; any thoughts?

Sorry, but this is entirely wrong. The vapour pressure of H2O near room temperature is very low (<0.03 atmospheres at 30-degC), so it could not sustain a bubble on its own. Even its contribution to an air or CO2 bubble would be trivial (~3% of volume at 30-degC for a large bubble, less in small ones because of surface effects). You can find more detail in contributions ##23,26,27&28 to the newsletter challenge question of 17 October.

WoW!! what is all this talk of CO2 and gaseous form of H2O??

Its air!!

Where did CO2 come from or 'gaseous water'...???

All water has dissolved air in it (unless its been boiled out or put in a vacuum to remove the air)... This air when subjected to temperature and pressure changes comes out of solution... Simple!

John.

"H2O in gaseous form" was pretty odd. And you would need a great deal of CO2 for it to come out as bubbles, due to its very high solubility. Perhaps it could be a significant contributor if you live somewhere that has suitable (?) untreated spring water.

Two thirds of the bubbles are made up of Hydrogen, and the other third are Oxygen. You can write anything here.

You can write anything here....

You've just proved it by writing RUBBISH!

I believe that was his point exactly!

IF you leave a glass of water alone long enough all the water will evaporate

out of it leaving an empty glass hence your bubbles

That must be the best reply yet....