Question

the percentage composition of oxygen is 80percent in a molecule. what does it mean?​

Answer 1

Answer:

The formula for glucose is C6H12O6. Let us calculate the mass percent of each of the elements in glucose.

From the formula, we can see the number of moles of each of the elements. Glucose has 6 carbon atoms, 12 hydrogen atoms and also 6 oxygen atoms. Let us now multiply each of the atoms by its molar mass. Thus, we arrive at the mass of each of the element in glucose.

We now divide each mass by mass of 1 mole of glucose to arrive at the mass fraction of each element. Multiplying this value by 100 gives the mass percentage of the elements.

The Example in Detail

Each mole of carbon has a mass of 12.01g/mol of carbon. This, we know, from the periodic table. So, 6 moles of carbon will have 12.01g/mol x 6 = 72.06g of Carbon. Similarly, 1 mole of Hydrogen has a mass of 1.008g/mol of Hydrogen. Therefore, 12 moles of Hydrogen will have the mass of 12 x 1.008 = 12.096g of Hydrogen.

Going by the same logic for Oxygen, 1 mole of oxygen has a mass of 16.00g/mol. Therefore, 6 moles of oxygen will have 16.00 x 6 = 96 g of Oxygen. Thus, 1 mole of Glucose (C6H12O6) has a total mass of 72.06 +12.096 + 96 = 180.16 g/mol

Calculating the Mass Percentage

To find out the mass % of the three elements of glucose, let us first calculate the mass fraction of each element in 1 mole of glucose. So, what do we mean by the mass fraction? It is the mass that each element contributes to the total mass of glucose. By multiplying this by 100, we get the mass percentage of each element.

Mass fraction of Carbon = 72.06g/180.16g = 0.4000

Therefore, mass % of Carbon= 0.4000×100 = 40.00%

Mass fraction of Hydrogen = 12.096/180.16 = 0.06714

Therefore, mass % of Hydrogen= 0.06714 x 100 = 6.714%

Mass fraction of Oxygen =96/180.16 = 0.53286

Therefore, mass% of Oxygen = 0.53286 x 100 = 53.286%

It is interesting to note that even if carbon and oxygen have an equal number of moles of the compound, their mass percentages are different. Oxygen has a higher value in this as its molar mass is higher than that of carbon.