calculate the number of carbon-12 atoms in 20.0 g of carbon-12

Question

I have to solve this question and I have no clue how to slove it can someone please help me. I need to have details to solve it thank you.

Answer 1

Hi Tina,

 One mole of Carbon-12 is exactly 12.0g, There are (20.0/12.0)moles with each mole having 6.022 x10²³ atoms.

So 20.0g of C-12 has (20.0/12.0) x 6.022 x10²³ atoms. You can now calculate the answer.

Answer 2

First what you need to know is Avogadro's number and what it means.

 

The number is: 6.02 x 10²³

 

This is the number of atoms or molecules in 1 mole of any substance.  For example, 1 mole of water has 6.02 x 10²³ molecules.  1 mole of carbon-12 has 6.02 x 10²³ atoms.

 

Second, you need to know how many moles there are in 20 grams of carbon-12.  One mole of anything is the same number of grams as the molecular mass.  Since the molecular mass of carbon-12 is 12, there are 12 grams in 1 mole of it, and therefore 20/12 = 5/3 moles in 20 grams.

 

So multiply 5/3 by 6.02 x 10²³ to get the number of atoms, and that gives you 10.03 x 10²³ or 1.003 x 10²⁴