Phthalocyanine is a large molecule used in printing inks and dyes for clothing due to its insolubility in most solvents, its chemical stability, and its intense blue color. Elemental analysis showed that it consists of 74.69% C, 3.525% H, and 21.77% N, and has a molar mass of 514.54 g/mol. What is the molecular formula for phthalocyanine? A)C₁₆H₉N₄ B)C₃₀H₈N₁₀ C)C₃₂H₁₈N₈ D)C₃₂H₄N₉ E)C₁₆H₁₈N₄

Question

Quizplus · Accepted Answer

1) Calculate the empirical formula: 
- C: 74.69 g / 12.01 g/mol ≈ 6.22 ≈ 6 
- H: 3.525 g / 1.008 g/mol ≈ 3.5 ≈ 3 
- N: 21.77 g / 14.01 g/mol ≈ 1.55 ≈ 2 
Empirical formula: C6H3N2 
2) Calculate the molecular mass: 
- Empirical formula mass: (6 x 12.01) + (3 x 1.008) + (2 x 14.01) = 226.26 g/mol 
- Actual molecular mass: 514.54 g/mol 
- Factor: 514.54 g/mol / 226.26 g/mol ≈ 2.28 ≈ 2 
3) Multiply the empirical formula by the factor: 
Empirical formula: C6H3N2 
Molecular formula: (C6H3N2) x 2 = C12H6N4 
The only choice that matches the molecular formula is C.

Phthalocyanine Is a Large Molecule Used in Printing Inks and Dyes