Can you determine the molecular formula of a substance from its percent composition?
No. You may obtain the empirical formula from percent composition but not the molecular formula.
Yes, you can determine the molecular formula of a substance from its percent composition. The percent composition of a substance gives the relative mass and quantity of each element present in a compound. To determine the molecular formula, you need to follow these steps:
1. Convert the percent composition to grams: Assume you have 100 grams of the substance. Convert the percentage of each element to grams by multiplying the percentage by 100 grams. This will give you the mass of each element in the substance.
2. Convert grams to moles: Calculate the number of moles for each element by dividing the mass of each element by its molar mass. The molar mass can be found on the periodic table and represents the mass of one mole of that element.
3. Determine the empirical formula: The empirical formula represents the simplest ratio of elements in a compound. Divide the number of moles of each element by the smallest number of moles calculated. This will give you the ratio of elements in the compound.
4. Determine the molecular formula: Finally, to find the molecular formula, you need to know the molar mass of the compound. Divide the molar mass of the compound by the molar mass calculated from the empirical formula. This will give you the number (n) of empirical formula units present in the molecular formula. Multiply the subscripts in the empirical formula by n to get the molecular formula.
By following these steps, you can determine the molecular formula of a substance from its percent composition.