Equations and Stoichiometry on SATII Chemistry


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Diatomic molecules

For the test, we must first memorize diatomic molecules. Some elements can not exist in nature on their own, and therefore form diatomic molecules. These molecules are: O2, I2, H2, N2, Cl2, F2, Br2.

Formula weight ( Molar mass)

We can calculate formula weight or molecular weight of a molecule by adding up the weight of each element, taken from the periodic table time the number of atoms of each element.

For example: H2O

H = 2*1 = 2

O = 1*16 = 16

2+16 = 18 g/mol

% Composition

(Mass of part/ total mass) * 100%

For example percent mass of Hydrogen in water is (2/18)*100%

Converting moles to atoms/molecules

When converting between moles and atoms or molecules, we must use Avogadro's number (6.02* 10^23 atoms or molecules per mole).

We always start with what is given to us. Then the units we want to get rid of go in the denominator to cancel and units we want to get go in the numerator.

For example, how many molecules of water are in 3 moles?

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