# Why is mole 12g of carbon-12?

1. Feb 6, 2005

### Raza

Hello, I am been tinkering about chemistry and they are bunch of things I don't get. I know I am asking stupid questions; that is why I didn't ask my teacher.

First of all,

Why is mole 12g of carbon-12?

How does the mole help us?

Since everything is made out of the elements listed in the periodic table of elements, how come hydrogen and oxygen from the air doesn't turn into water?

how come (H2O) as a whole has 1 mole while there are 2 mole of hydrogen?

What is the difference between particles, atoms and molecules?

ANY HELP WOULD BE GREATLY APPRECIATED!

2. Feb 6, 2005

### dextercioby

For the first question:check the definition.The definition of a mole,that is.As for the second,well it's important enough to pop up everywhere (especially) in chemistry...

There's very little H_{2} in the air (can u see why??),but a lot more oxygen and H_{2}O molecules...Sometimes the conditions for that reaction (very explosive,IIRC) are simply not met,just as in the case of N_{2} & O_{2}.By the same logics,we would have been dead long time ago,intoxicated with NO_{2} from the reaction of N_{2} & O_{2}.

Atoms are in the first approximation particles...However,molecules assume minimum 2 atoms and therefore cannot be considered particles...Do you know whata particle is...?

Daniel.

3. Feb 6, 2005

### Raza

I read the defination of a mole:
The amount of a substance that contains as many atoms, molecules, ions, or other elementary units as the number of atoms in 0.012 kilogram of carbon 12. 6.02 x 1023

But I don't get it, why is the mole 12g of carbon-12?

For the 2nd question, this is what I meant:
For example: How can the mole help us find the number of molecules I have in a 28.55 of Acetic Acid?

For the 3rd question, this is what I meant:
For example: Lets say I have three tanks; two with hydrogen and the other with oxygen. If I open the tanks all at the same time in a one closed room, will the room be filled with water?

And the last question:
AtomS and molecules are the same but Atom and molecules arn't?

Last edited: Feb 6, 2005
4. Feb 6, 2005

### dextercioby

Merely a convention.Before 1961 it was with O atoms and the # 16.They they thought of changing it.

Denote the molar mass through M.You know that

M grams of $CH_{3}-COOH$ ----------1 mole--------N_{A} molecules

28.55 grams of $CH_{3}-COOH$ ----------x moles---------y molecules...

It's not enough data...

What does that mean...?It lacks logics...

Daniel.

5. Feb 6, 2005

### Gokul43201

Staff Emeritus
A mole just refers to a certain number of anything (that number being the Avogadro Number, N_a). One mole of tennis balls is simply a collection of N_a number of tennis balls.

6. Feb 8, 2005

### pack_rat2

The "official" SI mole is the gram-mole, often written "mol," which contains 1 Avogadro's number of particles. The atomic/molecular/formula/etc. weight of a substance, in grams, is 1 mol of that substance. In engineering, pound-moles and kilogram-moles are often used, too. You could use ounce-moles or hundredweight-moles, too, if you're weird and it turns you on...

7. Feb 8, 2005

### DaveC426913

"Since everything is made out of the elements listed in the periodic table of elements, how come hydrogen and oxygen from the air doesn't turn into water?"

1] There is virtually no free hydrogen in the air. Any that accumulates will make its way to the top of the atmosphere and get blown away by solar wind.

2] If you put some H in a room with some O, nothing will happen. They need a small kick to get them to come together. An excellent way of giving them a kick is by lighting a match. The heat from the match gives enough energy to the H and the O atoms to allow them to combine. When they do so, they release energy (as heat) and stabilize at a lower energy level - the oxygen binding with two hydrogen atoms.

It gives off a lot of heat, produces vibrations, and the gasses are convernted to a new form that prefers to be a vapour.

And it happens very fast - i.e. light a match in a room full of hydorgen and BANG!

"how come (H2O) as a whole has 1 mole while there are 2 mole of hydrogen?"

The molar volume of a gas is a function - not of how many atoms - but of how many molecules - are in its particles.

Think of cars in rush hour. If the cars all had 4 passengers they wouldn't take up any more room on the road.

"What is the difference between particles, atoms and molecules?"

A particle is a generic term. Many things are particles. It needs qualifying, eg. subatomic particles.
An atom is any single element from the periodic table.
A molecule is any particle containing two or more bonded atoms.

Last edited: Feb 8, 2005
8. Feb 8, 2005

### Moonbear

Staff Emeritus
As others have pointed out, this is just a number chosen for convenience. Carbon is very common, so it is an easy molecule to use as a reference value. That's all.

Molecular weight is provided in units of grams/mol of a molecule, which you can use the periodic table to help you calculate for your molecule. Avogadro's number tells you how many molecules/mol. So with just a few simple multiplication steps, you can determine the number of molecules per gram of a particular substance.

If you're just covering molecules and moles right now, it's probably too soon for you to have covered the material that would help you understand this. When you cover thermodynamics, remember this question.

Molecules are made of two or more atoms bonded together. Atoms are the smallest "thing" (can't think of the better word at the moment) that has all the properties of the element and is made up of smaller particles, such as electrons, protons and neutrons. Does that help? So, to look at it the other way around, particles come together to form atoms, and atoms come together to form molecules.

9. Feb 8, 2005

### DaveC426913

"...smaller particles, such as electrons, protons and neutrons. Does that help? So, to look at it the other way around, particles come together to form atoms..."

Sure, subatomic particles. There are many things that are called particles.