Analysis of a volatile liquid showed that it is 54.5% carbon, 9.1% hydrogen, and 36.4% oxygen by mass. a separate 0.345-gram sample of its vapor occupied 120. ml at 100.°c and 1.00 atm. what is the molecular formula for the compound?

The molecular formula for the given organic compound is

Explanation:

We are given:

Percentage of C = 54.5 %

Percentage of H = 9.1 %

Percentage of O = 36.4 %

Let the mass of compound be 100 g. So, percentages given are taken as mass.

Mass of C = 54.5 g

Mass of H = 9.1 g

Mass of O = 36.4 g

To formulate the empirical formula, we need to follow some steps:

Step 1: Converting the given masses into moles.

Moles of Carbon =

Moles of Hydrogen =

Moles of Oxygen =

Step 2: Calculating the mole ratio of the given elements.

For the mole ratio, we divide each value of the moles by the smallest number of moles calculated which is 2.28 moles.

For Carbon =

For Hydrogen  =

For Oxygen  =

Step 3: Taking the mole ratio as their subscripts.

The ratio of C : H : O = 2 : 4 : 1

Hence, the empirical formula for the given compound is

Mass of empirical formula =  = 2(12) + 4(1) + 16 = 44 g/eq.

Now we have to determine the molar mass of compound by using ideal gas equation.

where,

P = pressure of gas = 1.00 atm

V = volume of gas = 120 mL = 0.120 L

T = temperature of gas =

w = mass of gas = 0.345 g

M = molar mass of gas = ?

R = gas constant = 0.0821 L.atm/mol.K

Now put all the given values in the above formula, we get:

For determining the molecular formula, we need to determine the valency which is multiplied by each element to get the molecular formula.

The equation used to calculate the valency is :

We are given:

Mass of molecular formula = 88.04 g/mol

Mass of empirical formula = 44 g/mol

Putting values in above equation, we get:

Multiplying this valency by the subscript of every element of empirical formula, we get:

Thus, the molecular formula for the given compound is