Glass And Candle Experiment | Why Does Water Rise?

Glass And Candle Experiment

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Why Does Water Rise?

It's a very popular experiment, from elementary school: put a burning candle on a dish filled with water, cover the candle with an inverted glass: after a little while, the candle flame goes out and the water level inside the glass rises.

Explanation:

There are two different effects: chemical and physical.

Chemical- oxygen and paraffin react. The burning produce water and carbon dioxide. Because twice as much oxygen is burned than carbon dioxide released, the air volume decreases.

Physical- the candle heats the air and expands it. This cancels the depletion of the oxygen temporarily and the water level stays down. When the oxygen is depleted, the candle goes out and the air cools. The volume of the air decreases and the water rises.

[fredstahl]

I remember this experiment from primary school 70 years ago. I was a skeptic then, because the explanation was the candle consumed the oxygen. That was it. It didn't match my observation of the air expanding with the heat and bubbling out, nor did they teach about the combustion products. This is a far more satisfactory explanation, matching my 10-YO observations. Back then, my explanations were dismissed. In fact, there is still much discussion about the complexity of this experiment.

[DANGJOS]

Low pressure causes the water to go up. Outside atmospheric pressure is higher and pushes up the water. The gases from the candle were hot then cooled

[larsuppling]

I work as a substitute teacher, and you just helped me teach a 10 year old about vacuum and air quality.
Thank you very much.

[DANGJOS]

@World of Engineering I would argue that the Physical explanation is *by far* the dominant effect. Here's why: Paraffin wax is a mix of hydrocarbons, but on average, it should have around 30 carbons per molecule. So let's use *C30H62.* The balanced equation is *C30H62+45.5O2->30CO2+31H2O*
In order to burn, the wax has to be in vapor form, so that means we started off with 46.5 units of gas, and ended with 61 units. *61/46.5=1.31*
so we actually end up with *more* gas at the end, not less. The water vapor will remain in vapor form unless enough is released for it to condense into liquid, and I would argue that this isn't the case.

This might lead one to believe that the pressure should actually increase, and not decrease, but this is not so.
Given our equation, there should be 31% more gas in the container than we started with, but this *assumes* air is 100% oxygen. The air is only about *21% oxygen, * so we're looking at more like about 6% more gas. But hang on, in *The Royal Institution's 2012 Christmas Lecture* they demonstrated that fire *cannot burn* in air with less than 15% oxygen, which means it's even less gas released (likely a couple percent or so or more). Lastly, oxygen doesn't even burn completely with wax anyway; products like carbon monoxide and soot are released.

So in reality, the burning candle adds *very little* volume of gas to the container, and is therefore insignificant. What is significant is the *temperature.* A candle flame burns at well over *1000 Kelvin.* Maybe even close to 2000. When the candle flame is covered, it reacts with a small portion of the oxygen in the container and then goes out. When it goes out, the gas quickly cools, and this causes the pressure on the inside to drop. If the humidity in the container is high enough, then perhaps the water vapor condensing plays a role, but I suspect this is a smaller effect.

[itsdancookie]

Thank u so much, i had this as my science assignment lol and i didnt have a candle or a glass jar so i saw ur vid and it helped me!

[arctomatic]

I remember using this for a science fair. Very useful and I ended up getting 2nd place. Thanks!

[marke]

The oxygen is being consumed, but that doesn’t mean it disappears. PV = nrT. You are not removing molecules from the cup therefore the physical effect is the only one acting.

[-korinzu]

TYSM YOU ANSWERED MY SCIENCE HOMEWORK😁😁😁

[rishidesai]

Thanks, you help me in my a science exhibition in my school .
Which is a little but important for me because I love science so teacher want have to experiment with explantion of it .

Thank you so much 💐

[clarkglymour]

Not an explantation. The reaction is (solid) C + (gas) O2 -> (gas) CO2, One gas molecule produced for each gas molecule consumed. So the number of gas molecules before and after burning is the same before and after burning the candle. By Avpgadro's law, the volumes should be the same.

[pawandorderspecialkittensu]

This is almost right, but takes a shortcut around the full explanation.

Everyone gets this wrong, they forget one thing: the hydrogen in paraffin making twice the number of molecules that the carbon dioxide does (the molecule number doesn't actually change, because for every CO2 in the vapor there's an H2O!) and the single biggest contributor: condensation.

See the end for the post of how this plays out when performed for a classroom. The fact about CO2 is correct, but everyone forgets that hydrogen is there and burned, making water vapor being made in the combustion!

Let's do the easy BLUF (Bottom Line Up Front) explanation.

For every CH2 parrafin molecule...we DON'T CARE, it's about the gas volume. The solid volume has almost no volume in comparison.
- Gas from the air consumed: 4 O2 molecules. (8 Oxygen atoms)
-This returns 2 CO2 molecules to the space. (4 Oxygen atoms)
-This returns 2 H2O molecules to the space (4 Oxygen atoms)

Basically: 4 molecules in, 4 molecules produced. Like thunderdome. Aside from the tiny change from the hydrogen at the ends of the wax molecule, the molecular number of GAS molecules in this combustion reaction does not change.. Almost at all.

BOTTOM LINE: It's more about physics and condensation than combustion equations. That water vapor shrinks somewhere around 1500:1 when it condenses as things get cold..

We forget hydrogen in chem diagrams that shorhand them in molecular diagrams when we only look at the inconsequentioal fuel part.

In comes condensation, which means that all those water molecules (half of the gas produced) shrinks about 1500:1, making sudden suction. that's what drives this, not the explanation in this video. I'd be happy to help remake it.

The physics plays out like this:

1) The setup is lit and the glass is down...and the candle burns, creating CO2 and H2O vapor.
2) The heat causes an increase in pressure, making the N2 and some O2 atoms to bubble out (usually) around the edge of the glass.
3) The candle runs out of both O2 and heating power, going extinct.
4) The sudden lack of heat causes a little cooling, sucking some of the water back up. a certain percentage.
5) The water vapor (50% of the remaining consumed-oxygen fraction gas) condenses on the glass and water surface with an ~15001 volume ratio.

When you run the math with some assumed scenarios, the condensation is the source of energy (pressure * volume -= energy) sufficient to lift the column of water.

[sanskrutijagdhane]

How did u made the red colour
Is that any chemical 🤔

[PiyushKumar-llkx]

Do a experiment with a plant in jar and a candle burning

[sara.aguilar]

this literally did my science hw. thanks

[lukavlahovic]

If you would have more candles would the water level be higher?

[solacetk]

Yayaya this is my project lmao now I have answers thank youuuu

[cserranoweb]

The oxygen depletes but a new gas is been formed: carbon dioxide, which compensates the oxygen loss. So, there must be another reason to explain why the water rises.

[robertokalamares]

Have this at homework but there's a question why they use food coloring pls help it is because you can see water clearly?

[anamikadasgupta]

grt experiment.amazing result!!keep it up!

[kalpanasonar]

Sir can this be done as science project for 9th std