Calculate the percent composition by mass of each element in NaClO3

Question

% Na

% Cl

% O

Answer 1

To solve this problem, you simply find the total mass of each element in the molecule and divide by the molecular mass.

First, note the mass of the molecule and each element:

Na molar mass = 22.99 g/mol

Cl molar mass = 35.45 g/mol

O molar mass = 16.00 g/mol

NaClO₃ molecular mass = 106.44g/mol

There is 1 Na atom per 1 NaClO₃ molecule. Therefore,

% Na in NaClO₃ = molar mass 1 Na atom / molar mass NaClO₃ = (22.99g/mol) / (106.44g/mol) * 100 = 21.60% Na

There is 1 Cl atom per 1 NaClO₃ molecule. Therefore,

% Cl in NaClO₃ = molar mass 1 Cl atom / molar mass NaClO₃ = (35.45g/mol) / (106.44g/mol) * 100 = 33.31% Cl

There are 3 O atoms per 1 NaClO₃ molecule. Therefore,

% O in NaClO₃ = 3 * molar mass 1 O Atom / molar mass NaClO₃ = (3 * 16.00g/mol) / (106.44 g/mol) * 100 = 45.10% O

You can check your work by adding together the three percentages of each element, which should equal 100%. There may be slight discrepancy due to rounding. 21.60% + 33.31% + 45.10% = 100.01%