Law of Definite Proportions

Lesson on the Law of Definite Proportions, one of the laws that led to modern atomic theory.

[Halfricky]

For anyone struggling: On the periodic table the mass of one hydrogen atom is 1.0078 g but we’re just gonna round it down to 1 g. The periodic table also says the mass of one oxygen atom is 15.999 g but we’re just gonna round it to 16 g. In every water molecule there is 2 Hydrogen and 1 Oxygen (H2O). So the mass of 2 Hydrogen is 2 g (1 g+1 g) and the mass of Oxygen is still 16 g because we only have 1 Oxygen in the formula for water. So in H2O, for every 16 g of Oxygen there are 2 g of Hydrogen. You can simplify this and say for every 8 g of Oxygen there is 1 g of Hydrogen. (16:2 = 8:1)

[mrJimmylavor]

i didn't understand but thanks for trying to explain...chemistry is very difficult for me...

[BensChemVideos]

@chromeney The decomposition of 18 g of water results in 16 grams of oxygen and 2 g of hydrogen because water always has the same 8:1 ratio of oxygen to hydrogen by mass.

Since each hydrogen atom weighs about 1 amu (and there are two of them in a water molecule), and each oxygen atom weighs about 16 amu (and there is one of them in a water molecule). The mass RATIO of oxygen to hydrogen is 16 amu / 2 amu = 8:1.

I hope this is helfpul.

[jammiedornan]

Sir amazing way of teaching simple sober and easy to understand

[DoctorWiley]

This video can confuse people, because you're comparing a compound on a mass level, instead of it's molecular level. That 8g:1g ratio is really .5mol (oxygen) for every 1 mol (hydrogen). So, to make them into real numbers, you say that for every 1 mol of oxygen there is 2 mols of hydrogen in any amount of pure water. It is better to be explained Chemistry on a molecular level because that is how it is always dealt with. The law of definite proportions is based on a molecular composition, not a mass composition.

[RealChipz]

I'm still kinda confused on the last part when you explained why it is always that ratio.

[amjaadharbi]

I understand so so .. anyway thank you so much!! You are better than my teacher 🙄

[zoyakhan-mlnx]

great video, thanks a lot. you saved my life. I couldn't understand the concept by reading

[smileyNUR]

what about the ratio of atomic weight?

[princeekwuribe]

What if its nitrogen and oxygen/ Is it still 8:1?

[aryangarg]

If I would take water 26g then what will happen??

Will it be decomposed only 18g leaving behind 8g or it will react as 26g

[MinTz]

what if its 16g of water? would it decomposes to 2g of hydrogen and 14g of oxygen?
wouldn't that makes the ratio 7:1?
I don't quite understand...

[zekroelite]

What is there not to It was so easy ... Thanks 😊

[joanangelicaholgado]

if i have 30grams of water would the ratio still be 8:1?

[eyeblue]

I'm Japanese.I learned law of definini proportions and it proust 1799.I don't know what is right.Which is correct
1797 or 1799？

[uification]

great video! i also like how you can hear a plane landing at 1:50

[chromeney]

from 18g. how did you got 2g of hydrogen and 16g of oxygen, how did you arrive at those.? can you pls explain? :)

[mahaibrahim]

thank you, this is such a helpfull vedio.

[justinyu]

can u replace my chem teacher she teaches for 45 minutes and no one gets it but i can watch this 4 minute video and i understand everything

[mariannebell]

Where does the 2.0 grams of Hydrogen come from?