Question

How many moles of ammonia weigh 85 g?

• A. 5 moles
• B. 10 moles
• C. 15 moles
• D. 20 moles

Answer 1

The correct option is A 5 moles

$\bullet$ Gram molecular mass is the sum of gram atomic mass of all the constituent atoms.

$\bullet$ The gram molecular mass of ammonia = gram atomic mass of nitorgen + (3 $\times$ gram atomic mass of hydrogen) = 14 + 3 = 17 g.

$\bullet$ Number of moles = $\frac{\text{Mass in grams}}{\text{Gram molecular mass}}$
So, number of moles in 85 g ammonia = $\frac{85}{17}$ = 5

Therefore, 5 moles of ammonia weighs 85 g.