When water boils, what are the bubbles that rise, and why do you say this?

Question

don't be afraid to be wrong, but if you think your right , please explain yourself.

please explain why you think your right. your answer is correct.

Answer 1

A number of people have proposed different gas compositions for your bubbles, some of which are correct, and some of which aren't. Listen to the top contributors, for they are right on the money. The process of heating water does not provide enough energy to dissociate water into hydrogen and oxygen. (Water can dissociate by electrolysis, which requires a sufficient voltage source and two electrodes.) As a test, you can hold a lighter above the surface of the water. If hydrogen or oxygen gas were released, it would combust. What are the gas bubbles made of then? At lower temperatures, they are the same composition as air (78%N2, 21% O2, 1%Ar for the most part). Air (or any gas for that matter) dissolves in water over time, and the amount of gas that dissolves depends on the temperature of the water and the pressure of the gas. As you heat water, the solubility of air decreases, and bubbles of air start to form. At the same time, the vapor pressure of water vapor (steam) starts to increase as you raise the temperature. As you near the boiling point, the bubbles are composed almost exclusively of water vapor. If you can get your hands on a graduated cylinder (or an inexpensive champagne glass), try the following experiment. Fill it up completely with tap water, then immerse it upside down in a pot of water. Try not to let any air bubbles in. Heat the water to a high enough temperature where you start to get significant accumulation of gas in the top of the graduated cylinder. Record the temperature and volume of gas by making a mark on the cylinder. Now try the same experiment with tap water that you have previously boiled. The experiment should be done within an hour of the boiling to minimize the amount of air that dissolves back into the water. Heat the water to the same temperature and record the volume. You should see a big difference beween the two experiments. More gas should be observed for the tap water that was not boiled, because it contains dissolved air as well as water vapor.

Answer 2

As water heats, its capability to hold dissolved gasses (air) in solution diminishes and the dissolved (mostly) air then starts coming out of solution as little bubbles. These will be seen on the bottom and sides of the pot. As water begins to boil in a pot the heat is concentrated at the bottom and some of the water in contact with the hot bottom will become steam bubbles and then collapse when cooled by the cooler surrounding water. Some rising circulation (convection) of the water will begin. Those little air bubbles will be gone by then. As the water gets hotter more steam bubbles are formed and some will rise to the top as the surrounding water becomes hotter. As boiling progresses to a full boil there will be rising steam bubbles which will escape. These together with the rising superheated water from the bottom will create the rolling turbulence.
I am supposing that the slight hissing sound that water makes when it begins to heat in a pot or a coffee maker may be associated with either the dissolution of the dissolved air or with the localized collapse of the initial tiny steam bubbles in direct contact with the heating element or the hot bottom..

Answer 3

The first bubbles to rise are dissolved air bubbles which, due to the increase in temperature, the air expands and forms the bubbles.
The next is bubbles of water vapour. Even though the water is not yet boiling, water has a vapour pressure at any temperature (hence evaporation of a pool of rain water).
As temperature increases, vapour pressure increases and the vapour forms small bubbles as it escapes from the liquid.
Finally, at its boiling point, masses of steam are all trying to leave the water at the same time so the bubbling activity becomes quite violent .. like a huge crowd trying to leave a football stadium through the gates all at the same time....quite a scramble isn't it ???

Answer 4

The bubbles are actually still water that is in a heated stage called water vapor.if water is heated to its boiling point(the temperature where the atmospheric pressure is surpassed by the excited stage of the water because of the heat applied to it), the liquid form of water becomes gaseous. since the gas state and the liquid state cannot exist in the same space, the gas bubbles up to the surface to be released in the atmosphere. if you place a cooler substance on top of the vapor, it cools and returns to its liquid form(water).

Answer 5

At initial stages, air dissolved in water is expelled in form of bubbles.

Later on hot water at the bottom of the container, which is less dense takes to the top as the cold portion goes to the bottom.

The convectional current continues to flow till all the water turns into vapor at boiling point and evaporates.

Answer 6

*From The International Collaborative Boiling Point Project:

“As water boils, the water turns into steam (also known as water vapor
or water gas.)

(..)

“First the water begins to form bubbles at the bottom near the heating device (see if this happens for you.) Then, the bubbles begin to rise until the bubbles begin to pop off the surface of the water and seemingly evaporate into the air.”

Where do the bubbles come from?

“The energy from the heating device first raises the temperature of the water. At a certain temperature, that energy is used to transform the water from its liquid state to its gaseous state (that's when you start seeing the bubbles form.) As the energy from the heating device goes into heating the water, the water temperature rises.

(..)

“But at a certain temperature, the heating energy goes only to turning the water into a gas. When that point is reached, your thermometer will not get any higher and you will have found the boiling point of your water.”

(..)

“As you heat up the water, you are breaking down the liquid molecule so that it can turn into a gas. Bubbles begin to be created in the base of the heating water first. But the pressure of the outside air will squash those bubbles at first because they don't have enough pressure inside them to stand up to the outside air pressure. As more energy goes into making those bubbles though, they will begin to be
able to stand up to the outside air pressure. When they get to the point where they can stand up to the outside air pressure, you'll see massive bubbles coming off of your water, the temperature of your water will top off and your boiling point will be reached.”

Stevens Institute of Technology
http://k12science.ati.stevens-tech.edu/curriculum/bp/background.html



*Boiling, a type of phase transition, is the rapid vaporization of a liquid, which typically occurs when a liquid is heated to its boiling point, the temperature at which the vapor pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding atmospheric pressure. Thus, a liquid may also boil when the pressure of the surrounding atmosphere is sufficiently reduced, such as the use of a vacuum pump or at high altitudes. Boiling occurs in three characteristic stages, which are nucleate, transition and film boiling. These stages generally take place from low to high surface temperatures, respectively.

*http://www.seps.org/oracle/oracle.archive/Physical_Science.Physics/2000.02/000950385832.3755.html
http://k12science.ati.stevens-tech.edu/curriculum/bp/background.html
http://www.geocities.com/thesciencefiles/bubbles/page.html

Answer 7

Well, distiled water actually doesn't boil, which leads my to belief that the excitation of H20 occurs at such a low temperature, that it picks up speed, and consequently mass, much faster than impurities within the body of fluid. I believe the makeup of H20 is weak enough of a bond that the impact that system goes through is enough to break the bond composing the element, thus, , when the hydrogen and oxygen fly away, they bond to other compositions in the water that are heavier than the excited H20, and float them on out

Answer 8

Any air dissolved in the water is driven out first, and then the bubbles contain steam.

Answer 9

If you watch closely you will see that before it starts boiling there are smaller bubbles sticking to the bottom and sides of the pot. As they heat up they expand and join together with the other bubbles and eventually can't stick to the bottom and sides any more and come up.

I believe it's actually a chemical reaction happening with the heat. The oxygen and hydrogen are separating and turning into gasses.

Answer 10

It would be gaseous water, i.e. steam. With reference to what the people above said, if the intramolecular bonds broke between the hydrogen and oxygen molecules in water then there would be an explosion. There is no air in the water, so the bubbles could be nothing other than gaseous water.