What mass of KNO_3 is required to prepare 2.5 L of a 3.25 M solution of potassium nitrate?

• A. 266 g
• B. 138 g
• C. 825 g
• D. 410 g

Answer: (C)

Verified step by step guidance

1. Identify the given information: volume of solution (V) = 2.5 L, molarity (M) = 3.25 mol/L, and the solute is potassium nitrate (KNO_3).
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 KNO_3 needed by multiplying the molarity by the volume: \(\text{moles of KNO}_3 = 3.25 \times 2.5\).
4. Find the molar mass of KNO_3 by adding the atomic masses of potassium (K), nitrogen (N), and oxygen (O): \(\text{molar mass} = 39.1 + 14.0 + (3 \times 16.0)\) g/mol.
5. Calculate the mass of KNO_3 required by multiplying the moles by the molar mass: \(\text{mass} = \text{moles of KNO}_3 \times \text{molar mass}\).