The Naked Scientists

The Naked Scientists Forum

Author Topic: How do I calculate the number of atoms in a given amount of something?  (Read 48071 times)

Offline jaiii

  • Sr. Member
  • ****
  • Posts: 114
    • View Profile
Hello.

 How to calculate how many atoms a particular element is located in one liter?

 Thank you
 goodbye
« Last Edit: 15/12/2011 08:10:32 by chris »


 

Offline bumblebee

  • First timers
  • *
  • Posts: 5
    • View Profile
You can use Avogadro's constant (6.0221415 10^23 mol-1) to work out the number of atoms there are :)
 

Offline widereader

  • Jr. Member
  • **
  • Posts: 25
    • View Profile
Convert liter to mole then mole to number of particles using Avogadro's number.
 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
You'll have to know what you're dealing with.

If it is a pure substance, then you can convert liters to grams using the density.  Then grams to moles using the atomic mass of the item.  Then, as mentioned above, moles to atoms or molecules.

If it is a mixture and you are only interested in a single solute, often it is already expressed in either grams per liter, or moles per liter.

An example:
1L of Ethanol has a density of 0.789 g/cm3.
So, 1L Ethanol * 1000 cm3/L * 0.789 g/cm3 = 789 g

Now, if you go to the Periodic Table for the atomic weights.
H = 1
C = 12
O = 16

So the molecular weight of Ethanol (CH3CH2OH) = 12 * 2 + 1*6 + 16*1= 46

So, you get:
789g /46 g/mol = 17.2 mol

17.2 mol * 6.022 x 1023 molecules / mol = 1.03 * 1025 molecules.

Your question was about atoms.  Ethanol has 9 atoms / molecule.

And you would get: 1.03*1025 molecules * 9 atoms/molecule = 9.3*1025 atoms.
 

The Naked Scientists Forum


 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums