The molecular mass of the compound is 90 amu. what is the molecular formula for c2h5o?

First let us get the molecular mass of the compound C2H5O.

C has molar mass of 12 amu, H is 1 amu, while O is 16 amu, therefore:

C2H5O = 12 amu * 2 + 1 amu * 5 + 16 amu = 45 amu

So to get 90 amu, simply double all the elements, therefore:

C4H10O2

Let us assume that the given formula of elements is empirical formula where elements have simplest whole number ratio

The empirical mass =  2 X atomic mass of carbon + 5 X atomic mass of hydrogen + at mass of O

The empirical mass = 2 X 12 + 5 + 16 = 45

The ratio of molecular mass and empirical mass = 90 / 45 = 2

Molecular formula is obtained by multiplying the empirical formula with this ratio / factor

molecular formula = 2 X (C2H5O) = C4H10O2

every chemical equation adheres to the law of conservation of mass, which states that matter cannot be created or destroyed. therefore, there must be the same number of atoms of each element on each side of a chemical equation.