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Percentage Composition, Exams of Chemistry

1 mol Cl molar mass NaCl = 58.44 g/mol. 22.99 g Na x 100 = 39.34 % Na. 58.44 g NaCl. Find the percentage composition of sodium nitrate.

Typology: Exams

2021/2022

Uploaded on 09/12/2022

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Dont forget to
multiply mass
by #of Moles
Percentage Composition
% Composition is the % by mass of each element in a
compound.
Ex: Find the percentage composition of sodium in sodium
chloride:
Na+ Cl - : formula is NaCl
1 mol Na x 22.99 g Na = 22.99 g Na
1 mol Na
1 mol Cl x 35.45 g Cl = 35.45 g Cl
1 mol Cl
molar mass NaCl = 58.44 g/mol
22.99 g Na x 100 = 39.34 % Na
58.44 g NaCl
Find the percentage composition of sodium nitrate.
Na+ NO3 - : formula is NaNO3
1 mol Na x 22.99 g Na = 22.99 g Na
1 mol Na
1 mol N x 14.01 g N = 14.01 g N
1 mol N
3 mol O x 16.00 g O = 48.00 g O
1 mol O molar mass NaNO3 = 85.00 g/mol
pf2

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Don’t forget to multiply mass by #of Moles

Percentage Composition

% Composition is the % by mass of each element in a

compound.

Ex: Find the percentage composition of sodium in sodium

chloride:

Na+^ Cl -^ : formula is NaCl

1 mol Na x 22.99 g Na = 22.99 g Na 1 mol Na 1 mol Cl x 35.45 g Cl = 35.45 g Cl 1 mol Cl molar mass NaCl = 58.44 g/mol 22.99 g Na x 100 = 39.34 % Na 58.44 g NaCl

Find the percentage composition of sodium nitrate.

Na+^ NO 3 -^ : formula is NaNO 3

1 mol Na x 22.99 g Na = 22.99 g Na 1 mol Na 1 mol N x 14.01 g N = 14.01 g N 1 mol N 3 mol O x 16.00 g O = 48.00 g O 1 mol O molar mass NaNO 3 = 85.00 g/mol

Once you find molar mass, you are just dividing the part (element) by the whole (compound) to get the percent composition 22.99 g Na x 100 = 27.05 % Na 85.00 g NaNO 3

  1. 01 g N x 100 = 16.48 % N 85.00 g NaNO 3 48.00 g O x 100 = 56.47% O 85.00 g NaNO 3

Why mass instead of moles? Isn’t 2/3 of the water molecule

hydrogen?

 Moles indicate the amounts of each atom needed to

make the molecule stable from an electron

standpoint.

2.02 g H x 100 = 11.21 % H 18.02 g H 2 O