Different constituent elements make up any chemical compound. In some chemical reaction calculations, you'll need to figure out how much of a certain element is in a specific compound. This can be determined by using the percent composition formula to get the element's percentage composition in a particular compound.
Formula
\%CE = \left( \frac{g_E}{g_T} \right) \times 100 where
- % CE is the percentage composition of element E.
- gE is the Total mass of element E present in compound T.
- gT is the total molar mass of compound T.
Mass Percentage (w/w)%
To describe the concentration of an element in a compound or a component in a combination, we utilize the idea of mass percentage composition.
Mass percentage composition can be calculated by dividing the mass of a component by the total mass of the combination. After that, multiply the ratio by 100. The mass percent (w/w)% is another name for it.
Solved Examples
Question 1: Calculate the percent composition of each element in water.
Solution:
The chemical formula of water is H2O. It contains 2 mole of Hydrogen and 1 mole of oxygen.
1 mole of Oxygen has molar mass of 16 g/mole.
1 × 16= 16 grams.
1 mole of Hydrogen has molar mass of 1.0108 g/mol.
1.008× 2 = 2.016 grams.
Total molar mass of H2O = 16+2.016 = 18.016 g/mol.
Formula of percentage composition,
%CE = (gE/gT)×100
Percentage composition of Hydrogen = (2.0016/18.016 )*100 = 11.19%
Percentage composition of oxygen = (16/18.016)*100 = 88.81%
Therefore, the percentage composition of hydrogen is 11.19% and oxygen is 88.81%.
Question 2: Calculate the Percentage composition of Carbon and Oxygen present in Glucose.
Solution:
The chemical formula of Glucose is C6H12O6.It contains 6 molecules of carbon, 12 molecules of hydrogen and 6 molecules of oxygen.
1 mole of carbon has molar mass of 12.01grams.
6 × 12.01= 72.06 grams.
1 mole of hydrogen has molar mass of 1.008 grams.
12 × 1.008 = 12.096 grams.
1 mole of oxygen has molar mass of 16grams.
6 × 16= 96 grams
Total molar mass of glucose = 72.06+12.096+96 = 180.16 g/mol.
Formula of percentage composition,
%CE = (gE/gT) × 100
Percentage composition of Carbon =(72.06/180.16) ×100 = 40%
Percentage composition of oxygen = (96/180.16) × 100 = 53.29%
Therefore, the percentage composition of carbon is 40% and oxygen is 53.29%.
Question 3: Calculate the percentage composition of all elements present in Calcium Hydroxide.
Solution:
The chemical formula of Calcium Hydroxide is Ca(OH)2.It contains 1 molecules of calcium, 2 molecules of hydrogen and 2 molecules of oxygen.
1 mole of calcium has molar mass of 40.01grams
1 × 40.01= 40.01 grams.
1 mole of hydrogen has molar mass of 1.008 grams.
2 × 1.008 = 2.016 grams.
1 mole of oxygen has molar mass of 16grams.
2 × 16= 32 grams.
Total molar mass of Calcium Hydroxide = 40.01+2.0016+32 = 74.102 g/mol.
Formula of Percentage composition,
%CE = (gE/gT)×100
Percentage composition of Calcium =(40.01/74.102)×100 = 54.12%
Percentage composition of oxygen = (32/74.102) × 100 = 43.2%
Percentage composition of hydrogen = (2.0016/74.102) × 100= 2.7%
Therefore, the percentage composition of calcium is 54.12%, oxygen is 43.2% and hydrogen is 2.7%.
Question 4: Calculate the percentage composition of nitrogen present in nitric acid.
Solution:
The chemical formula of nitric acid is HNO3. It contains 1 molecules of hydrogen, 1 molecules of nitrogen and 3 molecules of oxygen.
1 mole of hydrogen has molar mass of 1.008 grams.
1 × 1.008 = 1.008 grams.
1 mole of nitrogen has molar mass of 14.01grams.
1 × 1401= 14.01 grams.
1 mole of oxygen has molar mass of 16 grams
3 × 16= 48grams.
Total molar mass of nitric acid = 14.01+1.008+48 = 63.02 g/mol.
Formula of percentage composition,
%CE = (gE/gT)×100
Percentage composition of nitrogen =(14.01/63.02) ×100 = 22.23%.
Therefore, the percentage composition of nitrogen is 22.23%.
Question 5: Calculate the Percentage composition of potassium present in potassium permanganate .
Solution:
The chemical formula of potassium permanganate is KMnO4. It contains 1 molecules of hydrogen, 1 molecules of nitrogen and 3 molecules of oxygen.
1 mole of hydrogen has molar mass of 1.008 grams.
1 × 1.008 = 1.008 grams.
1 mole of nitrogen has molar mass of 14.01grams
1 × 14.01= 14.01 grams.
1 mole of oxygen has molar mass of 16grams.
3 × 16= 48grams.
Total molar mass of nitric acid = 14.01+1.008+48 = 63.02 g/mol.
Formula of percentage composition,
%CE = (gE/gT)×100
Percentage composition of nitrogen =(14.01/63.02) × 100 = 22.23%
Therefore, the percentage composition of nitrogen is 22.23%.
Question 6: Calculate the Percentage composition of Chlorine present in Hydrochloric acid.
Solution:
The chemical formula of Hydrochloric acid is HCl. It contains 1 molecules of hydrogen and 1 molecules of chlorine.
1 mole of hydrogen has molar mass of 1.008 grams.
1 × 1.008 = 1.008 grams.
1 mole of chlorine has molar mass of 35.45 grams.
1 × 35.45 = 35.45 grams.
Total molar mass of hydrochloric acid = 1.008+35.45 = 36.458 g/mol.
Formula of Percentage composition,
%CE = (gE/gT)×100
Percentage composition of chlorine = (35.45/36.458)×100 = 97.23%
Therefore, the percentage composition of chlorine is 97.23%.