A compound composed of only carbon and hydrogen is 25.2% hydrogen by mass. The empirical formula for this compound is ?

Since the compound contains 25.2% Hydrogen by mass and the compound is made of only carbon and hydrogen

Mass% of carbon = 100 - (mass% of hydrogen)

Mass% of carbon = 100 - 25.2

Mass% of carbon = 74.8%

Mass of each element in a given sample:

Let us take a 100 g sample of this compound

Since there is 25.2% hydrogen by mass, there is 25.2g hydrogen for every 100g of the compound

Similarly, there is 74.8 g carbon for every 100g of the compound

So, in a 100g sample:

Mass of Hydrogen = 25.2 grams

Mass of Carbon = 74.8 grams

Number of moles of each element in the 100g sample:

Moles of Carbon:

Molar mass of carbon = 12 g/mol

Number of moles = Given mass / molar mass

Number of moles = 74.8 grams / 12 g/mol

Moles of Carbon = 6.24 moles

Moles of Hydrogen:

Molar mass of Hydrogen = 1 g/mol

Number of moles = given mass / molar mass

Moles of Hydrogen = 25.2 / 1

Moles of Hydrogen = 25.2 moles

Empirical Formula:

The empirical formula of a compound is the simplest whole number ratio of the number of moles of the elements in the compound

Empirical formula  = Moles of Carbon : Moles of Hydrogen

Empirical formula = 6.24 / 25.2

Since we need a whole number ratio, and these numbers don't simplify to be whole numbers. we will multiply both of them with a common number which will make them both whole

Multiplying both the numbers by 25 makes them whole

Empirical formula = 6.24 * 25 / 25.2 (25)

Empirical formula = 156 / 630

further simplifying the numbers, we can divide them both by 2

Empirical formula = 78 / 315

dividing these numbers by 3

Empirical formula = 16 / 105

Therefore, the ratios of the moles of carbon to the moles of Hydrogen in the empirical formula is:   16 : 105

Empirical formula = C16H105