Calculate the mass % water in beryllium phosphite heptahydrate.
The correct answer and explanation is:
To calculate the mass percent of water in beryllium phosphite heptahydrate (BeHPO₃·7H₂O), follow these steps:
Step 1: Determine the molar mass of the compound.
First, calculate the molar masses of the components:
- Beryllium phosphite (BeHPO₃):
- Be = 9.012 g/mol
- H = 1.008 g/mol (x1 for 1 hydrogen atom)
- P = 30.974 g/mol
- O = 16.00 g/mol (x3 for 3 oxygen atoms)
- Water molecules (H₂O):
- H = 1.008 g/mol (x2 for 2 hydrogen atoms)
- O = 16.00 g/mol
- Water in beryllium phosphite heptahydrate (BeHPO₃·7H₂O):
There are 7 water molecules, so:- Molar mass of water in heptahydrate = 7 × 18.016 = 126.112 g/mol.
Step 2: Calculate the total molar mass of BeHPO₃·7H₂O.
The total molar mass of beryllium phosphite heptahydrate is the sum of the molar masses of BeHPO₃ and the water molecules:
Total molar mass = 89.994 g/mol (BeHPO₃) + 126.112 g/mol (7H₂O) = 216.106 g/mol.
Step 3: Calculate the mass percent of water.
The mass percent of water is calculated as: Mass percent of water=(Mass of waterTotal mass)×100\text{Mass percent of water} = \left( \frac{\text{Mass of water}}{\text{Total mass}} \right) \times 100 Mass percent of water=(126.112216.106)×100≈58.4%\text{Mass percent of water} = \left( \frac{126.112}{216.106} \right) \times 100 \approx 58.4\%
Explanation:
In this compound, beryllium phosphite heptahydrate contains seven molecules of water for every formula unit of BeHPO₃. By calculating the molar masses of both the anhydrous part (BeHPO₃) and the water molecules, and determining the ratio of the mass of water to the total mass, we find that approximately 58.4% of the mass of beryllium phosphite heptahydrate is due to water. This calculation is crucial in understanding how much water is present in the hydrated form compared to the anhydrous form.