Final answer:
To find the molecular formula of a dye, calculate the moles of each element from the given percent composition, find the empirical formula, and adjust it to match the provided molar mass.
Step-by-step explanation:
To determine the molecular formula of a dye with a given percent composition and molar mass, you first need the molar masses of individual elements (C, N, H), then use the percent composition to find the mass of each element in 100 g of the compound.
After that, you calculate the moles of each element by dividing by their respective atomic masses. Finally, you find the simplest whole number ratio of the elements to each other and then use the molar mass to determine the actual molecular formula.
As an example, consider a dye with 75.95% C, 17.72% N, and 6.33% H, with a given molar mass of 240 g/mol. In 100 g of the dye, there would be 75.95 g of C, 17.72 g of N, and 6.33 g of H.
Dividing these by the atomic masses (C: about 12 g/mol, N: about 14 g/mol, and H: about 1 g/mol) gives the number of moles of each element, and thus the ratio to find the empirical formula. Multiplying this ratio by appropriate factors to match the given molar mass of 240 g/mol would then yield the molecular formula.