Acompound is 7.74% hydrogen and 92.26% carbon by mass. at 100°c a 0.6883 g sample of the gas occupies 250 ml when the pressure is 820 torr. what is the molecular formula for this compound?

The molecular formula for the compound is

Explanation:

We are given:

Percentage of C = 92.26 %

Percentage of H = 7.74 %

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

Mass of C = 92.26 g

Mass of H = 7.74 g

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

Moles of Carbon =

Moles of Hydrogen =

For the mole ratio, we divide each value of the moles by the smallest number of moles calculated which is 7.68 moles.

For Carbon =

For Hydrogen =

The ratio of C : H = 1 : 1

The empirical formula for the given compound is

To calculate the molecular mass, we use the equation given by ideal gas equation:

PV = nRT

Or,

where,

P = pressure of the gas = 820 torr

V = Volume of gas = 250 mL = 0.250 L  (Conversion factor:  1 L = 1000 mL )

m = mass of gas = 0.6883 g

M = Molar mass of gas = ?

R = Gas constant =

T = temperature of the gas =

Putting values in above equation, 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 = 78.10 g/mol

Mass of empirical formula = 13 g/mol

Putting values in above equation, we get:

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

Hence, the molecular formula for the compound is

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