Calculate the formula (molar) mass of Na2S2O3.5H2O.
The Correct Answer and Explanation is:
To calculate the molar mass of sodium thiosulfate pentahydrate (Na₂S₂O₃·5H₂O), we need to sum the atomic masses of all the elements in the formula.
- Sodium (Na): Sodium has an atomic mass of approximately 22.99 g/mol. Since there are 2 sodium atoms, we multiply: 2×22.99=45.98 g/mol2 \times 22.99 = 45.98 \, \text{g/mol}2×22.99=45.98g/mol
- Sulfur (S): Sulfur has an atomic mass of approximately 32.07 g/mol. There are 2 sulfur atoms, so: 2×32.07=64.14 g/mol2 \times 32.07 = 64.14 \, \text{g/mol}2×32.07=64.14g/mol
- Oxygen (O): Oxygen has an atomic mass of approximately 16.00 g/mol. There are 3 oxygen atoms in Na₂S₂O₃, so: 3×16.00=48.00 g/mol3 \times 16.00 = 48.00 \, \text{g/mol}3×16.00=48.00g/mol
- Water (H₂O): For the 5 water molecules (5H₂O), we need to calculate the mass of each water molecule first.
- Hydrogen (H) has an atomic mass of approximately 1.008 g/mol, and oxygen (O) is 16.00 g/mol. The molar mass of H₂O is: 2×1.008+16.00=18.016 g/mol2 \times 1.008 + 16.00 = 18.016 \, \text{g/mol}2×1.008+16.00=18.016g/mol
- Since there are 5 water molecules: 5×18.016=90.08 g/mol5 \times 18.016 = 90.08 \, \text{g/mol}5×18.016=90.08g/mol
Now, summing up the masses of all components:45.98 (Na)+64.14 (S)+48.00 (O)+90.08 (H₂O)=248.20 g/mol45.98 \, (\text{Na}) + 64.14 \, (\text{S}) + 48.00 \, (\text{O}) + 90.08 \, (\text{H₂O}) = 248.20 \, \text{g/mol}45.98(Na)+64.14(S)+48.00(O)+90.08(H₂O)=248.20g/mol
Therefore, the molar mass of Na₂S₂O₃·5H₂O is approximately 248.2 g/mol.
Explanation:
The molar mass is the sum of the masses of all atoms present in a compound. To calculate this, you need to know the atomic masses of each element and multiply them by the number of atoms of each element in the compound. For hydrates, you also include the mass of water molecules in the calculation, as water is part of the crystalline structure of the compound. The final result gives you the mass of one mole of the compound, which can be useful for stoichiometric calculations in chemistry.
