How to calculate percent composition

Percent indicates one component in a 100 or part in a entirety. Because of this, percent composition of a compound is the percent by mass of each facet in the full mass of a compound. Anvarious other way of saying the same point is just how a lot in percent each element contributes to the total mass of a compound. The higher the portion composition, the greater the mass of the element existing in the compound. Mathematically, we have the right to expush percentage complace as:

Calculating portion composition

Now, let’s usage the above formula to calculate the percentage complace of each aspect in water— H2O. From the chemical formula of water, we know that 1 mole of water consists of 2 mol of hydrogen, H and 1 mol of oxygen, O. That is, we are assuming that:

1 mol of H2O contains 2 mol of H and 1 mol of O. But we perform know that the molar mass of hydrogen is about 1.01 g/mol and the molar mass of oxygen is around 16.00 g/mol. Because of this, we can calculate the mass of 1 mol of water, H2O as:

Calculating the mass of 1 mole of water

Now that we know the molar mass of water (whole), we can then calculate the percentage composition of hydrogen and oxygen in it as adheres to. For hydrogen, we understand that its molar mass is 1.01 g/mol, yet because we have 2 mol of it in water, then it complies with that we have to multiply the 2 mol of H by its molar mass. If we carry out, we will get 2.01 g, which is as a result of doing this: 2 mol x 1.01 g/mol = 2.02 g. We have the right to then use this worth, the molar mass of water, and also the percentage composition formula shown in equation 1 above to calculate the percent composition of hydrogen in water. If you are complying with alengthy, you will certainly alert that we deserve to set this calculation as:

Calculating percentage composition of H in water

Similarly, for oxygen, we recognize that its molar mass is 16.00 g/mol, but because we have 1 mol of it in water, then it adheres to that we should multiply the 1 mol of O by its molar mass. If we do, we will gain 16.00 g, which is as an outcome of doing: 1 mol x 16.00 g/mol = 16.00 g. We can then use this worth, the molar mass of water, and the percent complace formula illustrated in equation 1 above to calculate the percent composition of oxygen in water. If you are complying with alengthy, you will certainly notification that we deserve to set this calculation as:

Calculating the portion composition of oxygen in water

From the calculation, you have the right to see that the percent complace of hydrogen and also oxygen in water are 11.21% and also 88.79% respectively. If you include these worths together, you will notification they sum as much as 100%. This means regardless of whether water is from mars or from earth, as soon as it is pure water, its composition is resolved and will certainly always consist of 11.21% H and 88.79% O.


Because we know that you will certainly acquire 100% when you include the percentage complace of all the aspects in a chemical formula, then it follows that we deserve to subtract the percent composition of H from 100% to obtain that of oxygen. If you do, you will certainly get:

100% -11.21% = 88.79%.

Once you know the portion composition of all the aspects in a chemical formula, except one. You have the right to constantly usage this shortreduced to find its portion complace.

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Filed Under: Percentage composition Tagged With: Percentage composition, Percentage complace of H in water, Percentage composition of O in water


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