determine the formula or molecular mass of lead (II) phosphate.
The correct answer and explanation is:
The formula for lead (II) phosphate is Pb₃(PO₄)₂.
To explain this, let’s break down the components:
- Lead (II) refers to lead with a +2 charge. This means that a single lead ion (Pb²⁺) will need to combine with other ions in such a way that the total charge is neutral.
- Phosphate (PO₄)³⁻ is a polyatomic ion with a -3 charge. Phosphate contains one phosphorus atom bonded to four oxygen atoms, and this ion has an overall charge of -3.
Now, we need to balance the charges of the lead and phosphate ions in the formula. Since lead (II) has a +2 charge and phosphate has a -3 charge, it will take more than one phosphate ion to balance the charge of lead.
To achieve charge neutrality:
- Three Pb²⁺ ions will give a total positive charge of +6.
- Two PO₄³⁻ ions will give a total negative charge of -6.
Therefore, the formula must include three lead ions (Pb) and two phosphate ions (PO₄), resulting in the formula Pb₃(PO₄)₂.
Next, to calculate the molecular mass:
- The molar mass of lead (Pb) is approximately 207.2 g/mol.
- The molar mass of phosphorus (P) is approximately 30.97 g/mol.
- The molar mass of oxygen (O) is approximately 16.00 g/mol.
The molecular mass is calculated as follows:
- For lead: 3 × 207.2 = 621.6 g/mol
- For phosphate: 2 × (30.97 + 4 × 16.00) = 2 × (30.97 + 64.00) = 2 × 94.97 = 189.94 g/mol
Now, add these together:
- 621.6 + 189.94 = 811.54 g/mol
Thus, the molecular mass of lead (II) phosphate (Pb₃(PO₄)₂) is approximately 811.54 g/mol.