Chemistry: Combustion?

Question

The combustion of 28.8g of ammonia consumes _______g of oxygen.

A) 94.9

B) 54.1

C) 108

D) 15.3

E) 28.8

Answer 1

4 NH3 + 5 O2 >> 4 NO + 6 H2O

is the balanced equation

Moles NH3 = 28.8 g / 17.0307 g/mol = 1.69

Moles O2 needed = 1.69 x 5 / 4 = 2.11

Mass O2 = 2.11 mol x 32 g/mol = 67.6 g

sorry but I thing that this is the correct answer

Answer 2

This question is a puzzle. I did exactly the same calculation as Dr.A with the same answer which does not appear in your options.

Because nitrogen oxides are not easy sometimes, I searched some notes of mine and I found reference to this equation:

5 NH3 (g)  +  5 O 2 (g) →  4 NO (g)  +  6 H2O  (g)

I calculated 5mol NH3 = 85.155g

5 mol of O2 = 159.99g

Therefore, 28.8g NH3 require 159.99/85.155*28.8 = 54.10g O2

Very good until I checked and found that the equation was not balanced. This equation came from some notes on the catalytic oxidation of ammonia, published by the University of Minnesota.

I am lost - anybody else got any ideas?