Question

Given that 0.403 g of nitrogen combines with 0.0864 g of hydrogen and H is assigned an atomic mass of 1.00 amu calculate the atomic mass of nitrogen based on the formula NH.

Answer 1

Given,

Mass of nitrogen = 0.403 g

Mass of hydrogen = 0.0864 g

Atomic mass of H = 1 amu

Moles = mass / molar mass

Molar mass of H₂ = 1 x 2 = 2 g/mol

Moles of hydrogen = 0.0864 g / 2 g/mol = 0.0432 moles

Nitrogen combines with hydrogen hence the chemical equation is:

N₂ + 3H₂ → 2NH₃

As per the balanced chemical reaction, 3 moles of H₂ combines with 1 mole of N₂

or, 1 mole of H₂ combines with 1/3rd mole of N₂

Therefore, 0.0432 moles of H₂ will combine with (1/3 x 0.0432 moles of N₂)

Moles of N₂ = 0.0144 mol

Molar mass = mass / moles

Molar mass of N₂ = (0.043 g N₂) / (0.0144 mol N₂) = 2.986 g/mol of N₂

Atomic mass of N = 2.986/2 = 1.493 amu

Answer 2

If the molecular formula is NH, then it means there are 1 molecule of nitrogen every 1 molecule of hydrogen. In this case, the hydrogen atomic mass is 1 and its weight is 0.0864 grams. The nitrogen weight 0.403 grams and we need to find the atomic mass. The calculation should be:

(1/ 0.0864 gram) * 0.403 = 4.66

I'm not sure that there is NH molecule. The molecular weight of nitrogen should be 14 so the question might be wrong. If the reaction is N2 + 3 H2 → 2 NH3
Then the answer is: (3/ 0.0864 gram) * 0.403 = 14