Final answer:
To find a compound's molecular formula, use its percent composition to establish the empirical formula. Calculate the empirical formula mass and divide the compound's molar mass by this value. Multiply the empirical formula by the resultant whole number to get the molecular formula.
Step-by-step explanation:
Finding the Molecular Formula of a Compound
To determine the molecular formula of a compound, you first need to establish its empirical formula. This can be done by using its percent composition to calculate how many moles of each element are present in a specified mass of the compound. Assuming we have 100 g of the compound, this will simplify calculations, as the percentages can be directly converted to grams.
Once the amount of each element in grams is known, you then convert to moles using the atomic masses of these elements. This step provides you with the molar ratio of the elements, which is used to derive the empirical formula. Next, calculate the empirical formula mass (EFM), which is the sum of the atomic masses of all atoms in the empirical formula.
To find the molecular formula, divide the molar mass of the compound by the empirical formula mass to get a ratio, which should be a whole number or very close to one. Multiply all the subscripts in the empirical formula by this whole number to obtain the molecular formula of the compound.
In the context of comparing substances X and Y, if they have different compositions of carbon and hydrogen, it might indicate an example of the law of multiple proportions, providing insights on their chemical nature.