1. **State the problem:** Find the molar mass of ammonium phosphate, which has the chemical formula $\mathrm{(NH_4)_3PO_4}$. 2. **Formula and important rules:** The molar mass is the sum of the atomic masses of all atoms in the formula. Use the atomic masses: $\mathrm{N = 14}$, $\mathrm{H = 1}$, $\mathrm{P = 31}$, $\mathrm{O = 16}$. 3. **Calculate the number of each atom:** - Nitrogen (N): 3 ammonium ions, each with 1 N, total $3 \times 1 = 3$ N atoms. - Hydrogen (H): 3 ammonium ions, each with 4 H, total $3 \times 4 = 12$ H atoms. - Phosphorus (P): 1 atom. - Oxygen (O): 4 atoms. 4. **Calculate molar mass:** $$\text{Molar mass} = 3 \times 14 + 12 \times 1 + 1 \times 31 + 4 \times 16$$ $$= 42 + 12 + 31 + 64$$ $$= 149$$ 5. **Answer:** The molar mass of $\mathrm{(NH_4)_3PO_4}$ is **149 g/mol**.