Final answer:
The mass percent composition of lithium in Li₃PO₄ is calculated by the molar mass of the compound and then multiplying by 100%. This gives a percentage of approximately 17.98% lithium by mass in Li₃PO₄.
Step-by-step explanation:
To calculate the mass percent composition of lithium in Li₃PO₄, we first determine the molar mass of the entire compound and the molar mass of the lithium within it. We know that the atomic mass of lithium (Li) is approximately 6.94 g/mol and there are three lithium atoms in the compound. Thus, the total mass of lithium in the compound is 3 × 6.94 g/mol. For the molar mass of Li₃PO₄, we also have to consider the atomic masses of phosphorus (P) and oxygen (O), approximately 30.97 g/mol and 16.00 g/mol respectively. Therefore, the molar mass of Li₃PO₄ is 3(6.94) + 30.97 + 4(16.00) g/mol. Finally, we divide the mass of the lithium by the total mass of the compound and multiply by 100% to get the percentage of lithium.
Using the atomic masses:
Mass of Lithium: 3 × 6.94 = 20.82 g/mol
Molar mass of Li₃PO₄: 20.82 (Li) + 30.97 (P) + 64.00 (4×16.00 O) = 115.79 g/mol
Mass percent of Lithium = (Mass of Lithium / Molar mass of Li₃PO₄) × 100% = (20.82 / 115.79) × 100% = 17.98%