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I dont understand what moles are in chemistry.

Im doing gcse chemistry and i dont understand the concept of moles. for example, a question states:

Oxygen gas has the formula O2.
Calculate the number of oxygen atoms in 3.50mol of oxygen gas.
(Avogadro constant = 6.02×1023)

And the answer is: 2 x 3.5 (1) (= 7(.0))
7(.0) x 6.02 x 1023 (1) (= 4.214 x 1024)

But why would you multiple 3.5 by 2? Is it because there are two oxygen atoms? But isnt O2 only one mole of oxygen? And in a mole there are 6.02 x 10*23 atoms, so what is a "mole" referring to here if there are only two oxygen atoms??? please help my chemistry exam is on tuesday and i have no idea what moles are

Reply 1

eallistar

Original post by seagull11

Im doing gcse chemistry and i dont understand the concept of moles. for example, a question states:
Oxygen gas has the formula O2.
Calculate the number of oxygen atoms in 3.50mol of oxygen gas.
(Avogadro constant = 6.02×1023)
And the answer is: 2 x 3.5 (1) (= 7(.0))
7(.0) x 6.02 x 1023 (1) (= 4.214 x 1024)
But why would you multiple 3.5 by 2? Is it because there are two oxygen atoms? But isnt O2 only one mole of oxygen? And in a mole there are 6.02 x 10*23 atoms, so what is a "mole" referring to here if there are only two oxygen atoms??? please help my chemistry exam is on tuesday and i have no idea what moles are

Hi a level chem student here - basically O2 is a molecule and O by itself is an atom so when you x2 it is because there are 2 atoms of O.

Reply 2

eallistar

Original post by seagull11

Im doing gcse chemistry and i dont understand the concept of moles. for example, a question states:
Oxygen gas has the formula O2.
Calculate the number of oxygen atoms in 3.50mol of oxygen gas.
(Avogadro constant = 6.02×1023)
And the answer is: 2 x 3.5 (1) (= 7(.0))
7(.0) x 6.02 x 1023 (1) (= 4.214 x 1024)
But why would you multiple 3.5 by 2? Is it because there are two oxygen atoms? But isnt O2 only one mole of oxygen? And in a mole there are 6.02 x 10*23 atoms, so what is a "mole" referring to here if there are only two oxygen atoms??? please help my chemistry exam is on tuesday and i have no idea what moles are

So when you X the 3.5 by 2 it tells you the number of moles of oxygen in O2 not just O

Reply 3

eallistar

Original post by seagull11

Im doing gcse chemistry and i dont understand the concept of moles. for example, a question states:
Oxygen gas has the formula O2.
Calculate the number of oxygen atoms in 3.50mol of oxygen gas.
(Avogadro constant = 6.02×1023)
And the answer is: 2 x 3.5 (1) (= 7(.0))
7(.0) x 6.02 x 1023 (1) (= 4.214 x 1024)
But why would you multiple 3.5 by 2? Is it because there are two oxygen atoms? But isnt O2 only one mole of oxygen? And in a mole there are 6.02 x 10*23 atoms, so what is a "mole" referring to here if there are only two oxygen atoms??? please help my chemistry exam is on tuesday and i have no idea what moles are

Avogadros is how many atoms are in any mol of anything in the world so you then times your total number of moles (7) by avogadros to find the number of atoms im O2

Reply 4

klafow

Original post by seagull11

Im doing gcse chemistry and i dont understand the concept of moles. for example, a question states:
Oxygen gas has the formula O2.
Calculate the number of oxygen atoms in 3.50mol of oxygen gas.
(Avogadro constant = 6.02×1023)
And the answer is: 2 x 3.5 (1) (= 7(.0))
7(.0) x 6.02 x 1023 (1) (= 4.214 x 1024)
But why would you multiple 3.5 by 2? Is it because there are two oxygen atoms? But isnt O2 only one mole of oxygen? And in a mole there are 6.02 x 10*23 atoms, so what is a "mole" referring to here if there are only two oxygen atoms??? please help my chemistry exam is on tuesday and i have no idea what moles are

A mole is just a name for a specific number of something. It's like how a 'pair' refers to 2, and a 'dozen' refers to 12. In this case, a 'mole' refers to 6.02 x 10^23, a number known as the avogadro constant

3.5 moles of oxygen gas contains (6.02 x 10^23) *3.5 oxygen molecules, because oxygen exists in its diatomic form usually. That's O₂. However, the question wants you to say how many oxygen atoms there are in 3.5 moles of oxygen gas. Since there are two oxygen atoms in one molecule of oxygen, you'd multiply by two to get the total number of oxygen atoms.
So your answer should be 3.5 * 2 * (6.02 x 10^23), which according to my trusty calculator is equal to 4.214 x 10^24.

I hope that makes sense, feel free to let me know if it doesn't 🙂

Reply 5

Nitrotoluene

Since one mole of O2 contains 2 oxygen atoms, you can multiply 3.50 mol by 2 to get:

3.50 mol x 2 = 7.00 mol of oxygen atoms
So, the correct calculation is:
3.50 mol x 2 = 7.00 mol of oxygen ==> 7.00 mol x 6.022 x 10^23 = 4.214 x 10^24 oxygen atoms