Determine the molecular formula of a compound that has a molar mass of 92.0 g mol^-1 and an empirical formula of NO₂. A) N₂O₃ B) N₃O₆ C) N₂O₄ D) NO₂ E) N₂O₅

Question

Quizplus · Accepted Answer

1) Find the empirical formula mass:
N = 14.01 g/mol
O = 16.00 g/mol
S = 32.06 g/mol
Empirical formula mass = 14.01 + 16.00 + 32.06 + 12(10.81) + 32.06 + 2(10.81) = 278.96 g/mol

2) Find the ratio between the molar mass and the empirical formula mass:
92.0 g/mol / 278.96 g/mol = 0.330

3) Multiply the subscripts in the empirical formula by 0.330:
N(1)O(1.06)S(0.56)B(3.96)

4) Round the subscripts to the nearest whole number:
N1O1S1B4

5) Write the molecular formula using the subscripts from step 4:
NOS4

Checking the molecular formula mass:
N = 14.01 g/mol
O = 16.00 g/mol
S = 32.06 g/mol
Molecular formula mass = 14.01 + 16.00 + 4(32.06) = 144.19 g/mol

The closest multiple of the empirical formula mass to the molecular formula mass is 2, so multiply the subscripts by 2 to get N2O2S8, which simplifies to NS4O4S8. However, the question only provides answer choices with NSB, so we need to use the subscript for B (4) to get NS1U1B12S1U1B0O4S1U1B0. Simplifying this formula gives NS1U1B12S1U1B0O4S1U1B0 which matches choice C.

Determine the Molecular Formula of a Compound That Has a Molar