Calculate the moles of 257.354 g of K2CrO4.
The correct answer and explanation is:
To calculate the moles of K2CrO4 (potassium chromate), follow these steps:
Step 1: Find the molar mass of K2CrO4
First, determine the atomic masses of each element in the formula:
- Potassium (K) has an atomic mass of approximately 39.1 g/mol.
- Chromium (Cr) has an atomic mass of approximately 52.0 g/mol.
- Oxygen (O) has an atomic mass of approximately 16.0 g/mol.
Now, calculate the molar mass of K2CrO4:
- 2 atoms of potassium (K): 2×39.1=78.22 \times 39.1 = 78.2 g/mol.
- 1 atom of chromium (Cr): 1×52.0=52.01 \times 52.0 = 52.0 g/mol.
- 4 atoms of oxygen (O): 4×16.0=64.04 \times 16.0 = 64.0 g/mol.
The total molar mass of K2CrO4 is: 78.2+52.0+64.0=194.2 g/mol.78.2 + 52.0 + 64.0 = 194.2 \, \text{g/mol}.
Step 2: Calculate the moles of K2CrO4
Now, use the formula for moles: moles=massmolar mass.\text{moles} = \frac{\text{mass}}{\text{molar mass}}.
Given the mass of K2CrO4 is 257.354 g, and the molar mass is 194.2 g/mol: moles=257.354 g194.2 g/mol≈1.326 mol.\text{moles} = \frac{257.354 \, \text{g}}{194.2 \, \text{g/mol}} \approx 1.326 \, \text{mol}.
Conclusion:
The number of moles in 257.354 g of K2CrO4 is approximately 1.326 moles.
This calculation involves first determining the molar mass of a compound by adding the atomic masses of each element in the compound. Then, to find the moles, you divide the given mass by the molar mass. This process allows you to relate the amount of substance in grams to the number of moles, which is important in chemical reactions and stoichiometric calculations.