Moles and masses
The amount of substance that contains the same number of particles as there are atoms in 12 g of carbon-12., The amount of matter an object contains. Mass is measured in grams (g). and Total mass of the relative atomic masses of all the atoms in a given formula. are closely related.
\(moles = \frac{mass~(g)}{M_r} \)
You can imagine these properties of a substance in a triangle. You can reconfigure the triangle to calculate a substanceâs mass, moles or Mr.
Cover the value you want to find and perform the operation between the remaining two values
Calculating masses
Example:
Calculate the mass of 0.25 mol of carbon dioxide molecules (Mr of CO2 = 44).
Mass = mol Ă Mr
= 44 Ă 0.25
= 11 g
Calculating amounts in moles
Example:
Calculate the number of moles in 36 g of water (Mr of water = 18).
\(moles = \frac{mass~(g)}{M_r}\)
\(moles = \frac{36}{18}\)
=2 mol