Calculate the molar mass for Cr(NO3)2 (show calculation): b. Calculate the number of moles of Cr(NO3)3 contained in 25.0 grams of Cr(NO3)3:
The Correct Answer and Explanation is:
a. Molar mass of Cr(NO3)2:
To calculate the molar mass of Cr(NO3)2, we need to add up the atomic masses of each element in the compound.
- Chromium (Cr): The atomic mass of chromium is 52.00 g/mol.
- Nitrogen (N): The atomic mass of nitrogen is 14.01 g/mol. There are 2 nitrogen atoms in the compound, so the total mass contributed by nitrogen is 2×14.01=28.02 g/mol2 \times 14.01 = 28.02 \, \text{g/mol}2×14.01=28.02g/mol.
- Oxygen (O): The atomic mass of oxygen is 16.00 g/mol. There are 6 oxygen atoms (since each nitrate group has 3 oxygen atoms, and there are 2 nitrate groups), so the total mass contributed by oxygen is 6×16.00=96.00 g/mol6 \times 16.00 = 96.00 \, \text{g/mol}6×16.00=96.00g/mol.
Now, we can calculate the molar mass of Cr(NO3)2:Molar mass=52.00 g/mol (Cr)+28.02 g/mol (N)+96.00 g/mol (O)=176.02 g/mol.\text{Molar mass} = 52.00 \, \text{g/mol (Cr)} + 28.02 \, \text{g/mol (N)} + 96.00 \, \text{g/mol (O)} = 176.02 \, \text{g/mol}.Molar mass=52.00g/mol (Cr)+28.02g/mol (N)+96.00g/mol (O)=176.02g/mol.
b. Calculate the number of moles of Cr(NO3)3 in 25.0 grams:
To calculate the number of moles, we use the formula:Moles=Mass (g)Molar mass (g/mol).\text{Moles} = \frac{\text{Mass (g)}}{\text{Molar mass (g/mol)}}.Moles=Molar mass (g/mol)Mass (g).
Given:
- Mass = 25.0 grams.
- Molar mass of Cr(NO3)3 = (52.00 g/mol for Cr) + (3 × 14.01 g/mol for N) + (9 × 16.00 g/mol for O).
Molar mass of Cr(NO3)3=52.00+42.03+144.00=238.03 g/mol.\text{Molar mass of Cr(NO3)3} = 52.00 + 42.03 + 144.00 = 238.03 \, \text{g/mol}.Molar mass of Cr(NO3)3=52.00+42.03+144.00=238.03g/mol.
Now, calculate the moles:Moles=25.0 g238.03 g/mol≈0.105 moles.\text{Moles} = \frac{25.0 \, \text{g}}{238.03 \, \text{g/mol}} \approx 0.105 \, \text{moles}.Moles=238.03g/mol25.0g≈0.105moles.
Final Answers:
- a. The molar mass of Cr(NO3)2 is 176.02 g/mol.
- b. The number of moles of Cr(NO3)3 in 25.0 grams is approximately 0.105 moles.
