Here's how to calculate the mass of 3 moles of ammonia:

1. Find the molar mass of ammonia (NH₃):

* Nitrogen (N) has a molar mass of 14.01 g/mol

* Hydrogen (H) has a molar mass of 1.01 g/mol

* Molar mass of NH₃ = 14.01 g/mol + (3 * 1.01 g/mol) = 17.04 g/mol

2. Calculate the mass of 3 moles of ammonia:

* Mass = (number of moles) * (molar mass)

* Mass = 3 mol * 17.04 g/mol = 51.12 g

Therefore, the mass of 3 moles of ammonia is 51.12 grams.