Answer:338.7786
Explanation:The formula weight of the monovalent ion **AuCl₄⁻** (tetrachloroaurate) can be calculated as follows:
1. First, compute the number of each atom in AuCl₄⁻:
- Gold (Au): 1 atom
- Chlorine (Cl): 4 atoms
2. Look up the atomic weights for each element:
- Atomic weight of Au: 196.966569 g/mol
- Atomic weight of Cl: 35.453 g/mol
3. Compute the sum of products of the number of atoms and their atomic weights:
- Molar mass (AuCl₄⁻) = (Count (Au) × Weight (Au)) + (Count (Cl) × Weight (Cl))
- Molar mass (AuCl₄⁻) = (1 × 196.966569) + (4 × 35.453) = **338.7786 g/mol**
Therefore, the formula weight of the monovalent ion **AuCl₄⁻** is approximately **338.78 g/mol**¹.
