Molecular formula of sodium nitrate $NaNO3$ consists of one sodium atom $Na$, one nitrogen atom $N$, and three oxygen atoms $O$.

The molar mass of sodium is 22.99 g/mol, nitrogen is 14.01 g/mol, and oxygen is 16.00 g/mol.

So, the molar mass of one molecule of sodium nitrate can be calculated as follows:

Molar mass = 22.99 + 14.01 + $3\ast 16.00$ = 22.99 + 14.01 + 48.00 = 86 g/mol

Therefore, the mass of one molecule of sodium nitrate is 86 g/mol.