The insulating and packing material Styrofoam is a polymer of styrene.Find the molecular formula of styrene given its percent composition: 92.25% C,7.75% H.The approximate molar mass of styrene is 104 g/mol.

Question

Quizplus · Accepted Answer

To find the molecular formula of styrene, we need to first find the empirical formula.

Step 1: Assume we have a 100 g sample of styrene. 
C: 92.25 g (92.25% of 100 g) 
H: 7.75 g (7.75% of 100 g)

Step 2: Convert the mass of each element to moles. 
C: 92.25 g / 12.01 g/mol = 7.686 mol 
H: 7.75 g / 1.01 g/mol = 7.673 mol

Step 3: Divide each mole value by the smallest mole value. 
C: 7.686 mol / 7.673 mol ≈ 1 
H: 7.673 mol / 7.673 mol = 1

Step 4: The empirical formula is CH, indicating that there is one carbon atom for every hydrogen atom in styrene.

Step 5: To find the molecular formula, we need to know the molar mass of the compound. 
Molar mass of styrene = 104 g/mol

Step 6: Divide the molar mass by the empirical formula mass to find the ratio of molecular formula to empirical formula. 
104 g/mol / 26 g/mol = 4

Step 7: Multiply the empirical formula by the ratio found in step 6 to get the molecular formula. 
CH x 4 = C4H4

However, this is not one of the answer choices. We can simplify C4H4 to C4H4/4 = C2H2.

The molecular formula for styrene is C8H8 (which can be written as C8H8/2), which is closest to choice D, C8H₈.

The Insulating and Packing Material Styrofoam Is a Polymer of Styrene.Find