Question

In 2006, a Russian team discovered an interesting molecule they called "sulflower" because of its shape and because it was based on sulfur. It is composed of 57.17% S and 42.83% C and has a molar mass of 448.70 g/mol. Determine the empirical and molecular formulas of "sulflower."

Answer 1

Answer: The empirical and molecular formula for the given organic compound is
`C_2S` and
`C_(16)S_8` respectively.

Step-by-step explanation:

We are given:

Percentage of C = 42.83 %

Percentage of S = 57.17 %

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

Mass of C = 42.83 g

Mass of S = 57.17 g

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

• Step 1: Converting the given masses into moles.

Moles of Carbon =
`\frac{\text{Given mass of Carbon}}{\text{Molar mass of Carbon}}=(42.83g)/(12g/mole)=3.57moles`

Moles of Sulfur =
`\frac{\text{Given mass of Sulfur}}{\text{Molar mass of Sulfur}}=(57.17g)/(32g/mole)=1.79moles`

• 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 1.79 moles.

For Carbon =
`(3.57)/(1.79)=1.99\approx 2`

For Sulfur =
`(1.79)/(1.79)=1`

• Step 3: Taking the mole ratio as their subscripts.

The ratio of C : S = 2 : 1

Hence, the empirical formula for the given compound is
`C_2S_1=C_2S`

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:

`n=\frac{\text{molecular mass}}{\text{empirical mass}}`

We are given:

Mass of molecular formula = 448.70 g/mol

Mass of empirical formula = 56 g/mol

Putting values in above equation, we get:

`n=(448.70g/mol)/(56g/mol)=8`

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

`C_((8* 2))S_((8* 1))=C_(16)S_8`

Thus, the empirical and molecular formula for the given compound is
`C_2S` and
`C_(16)S_8`