Which of the following processes will determine the number of moles of a sample? a. dividing the mass of the sample by its molar mass b. multiplying the mass of the sample by its molar mass c. dividing the mass of the sample by avogadro's number d. multiplying the mass of the sample by avogadro's number

The answer is: A. Dividing the mass of the sample by its molar mass.

For example, sample of ammonia:

m(NH₃) = 17.031 g; mass of ammonia.

M(NH₃) = Ar(N) + 3 · Ar(H) · g/mol.  

M(NH₃) = 14.007 + 3 · 1.008 · g/mol.  

M(NH₃) = 17.031 g/mol.  

n(NH₃) = m(NH₃) ÷ M(NH₃).

n(NH₃) = 17.031 g ÷ 17.031 g/mol.

n(NH₃) = 1.0 mol; amount of ammonia.

The molar mass (M) is the mass of a given substance (in this example ammonia) divided by the amount of substance.