How many grams of K2Cr2O7 are required to prepare 250 mL of a 0.10 M solution?

• A. 2.45 g
• B. 3.75 g
• C. 7.36 g
• D. 5.89 g

Answer: (C)

Verified step by step guidance

1. Identify the given information: volume of solution (V) = 250 mL and molarity (M) = 0.10 M. Convert the volume from milliliters to liters because molarity is expressed in moles per liter. Use the conversion: \$1\, \text{L} = 1000\, \text{mL}\(, so \)V = \frac{250}{1000} = 0.250\, \text{L}$.
2. Recall the definition of molarity: \(M = \frac{\text{moles of solute}}{\text{liters of solution}}\). Rearrange this to find moles of solute: \(\text{moles} = M \times V\).
3. Calculate the moles of \(\mathrm{K_2Cr_2O_7}\) needed: \(\text{moles} = 0.10\, \mathrm{mol/L} \times 0.250\, \mathrm{L}\).
4. Find the molar mass of \(\mathrm{K_2Cr_2O_7}\) by summing the atomic masses: Potassium (K) = 39.10 g/mol, Chromium (Cr) = 52.00 g/mol, Oxygen (O) = 16.00 g/mol. Calculate: \$2 \times 39.10 + 2 \times 52.00 + 7 \times 16.00$ g/mol.
5. Convert moles to grams using the molar mass: \(\text{mass} = \text{moles} \times \text{molar mass}\). This will give the grams of \(\mathrm{K_2Cr_2O_7}\) required to prepare the solution.