Today we learned about the mole! A mole is the number of atoms f that element equal to the number of atoms in exactly 12.0 grams of carbon-12.
- For example, 1 mole of Carbon (c) atoms is 12.01 g,
- and 1 mole of Calcium (Ca) atoms is 40.1 g.
For the diatomic molecules, plus phosphorus and sulphur, are however different when not joint into a compound. The diatomic seven (hydrogen, oxygen, nitrogen, chloride, bromine, iodide, and fluoride) have 2.
- For example, hydrogen is 2, therefore 2(1.0 g) = 2.0 mol.
- Another example is oxygen. Oxygen is 2, therefore 2(16.0 g) = 32.0 mol.
When finding the molar mass in compounds, the molar mass of all atoms must be added:
- H2o (water) has 2 hydrogen atoms and 1 oxygen atom. The mass of hydrogen is 2(1.0 g) = 2.0 mol and oxygen is 1(16.0 g) = 16.0 mol. Together, the molar mass of the compound is 18 mol
To find the mass in moles of a compound we use g/mol. To find the number of moles in a compound we use mol/g. For example:
- To find the mass of 2.5 moles of water..
2.5 mol of H2O x (18.0 g / 1 mol) = 45 g
H = 2(1.0)
O = 1(16.0)
= 18.0 g / mol
- To find the number of moles in a 391 g sample of nitrogen dioxide..
391 g of NO2 x (1 mol / 46 g) = 8.5 mol
N = 1(14.0)
O = 2(16.0)
= 46 g / mol
Here's a handy clip in finding molar mass:
That is all. Mr. Doktor is the best!
-- Jael Lumba
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