Question

A major textile dye manufacturer developed a new yellow dye. The dye has a percent composition of 75.95% C, 17.72% N, and 6.33% H by mass with a molar mass of about 240 g/mol. Determine the molecular formula of the dye.

Answer 1

Given:

Percentage composition:

C = 75.95%

N = 17.72%

H = 6.33%

Molar mass = 240 gm

To Find:

The molecular formula of the dye.

Calculation:

- Let the mass of compound be 100 gm.

⇒ Mass of C = 75.95 gm

⇒ Mass of N = 17.72 gm

⇒ Mass of H = 6.33 gm

- No of moles:

C = 75.95/12 = 6.33

N = 17.72/14 = 1.27

H = 6.33/1 = 6.33

- Simplest ratio

C = 6.33/1.27 = 4.98 ≈ 5

N = 1.27/1.27 = 1

H = 6.33/1.27 = 4.98 ≈ 5

- Empirical formula = C5NH5

- Empirical formula mass = 12 × 5 + 14 + 1 × 5 = 79 gm

- n = Molar mass/ Empirical formula mass

⇒ n = 240/79 = 3.04 ≈ 3

- Molecular formula = Empirical formula × n

⇒ Molecular formula = C15N3H15

(Note: The molar mass given is approximate. Actual molar mass is 237 gm/mol)

Answer 2

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