What is the percent by mass of a solution prepared by dissolving 25 g of KNO_3 in 400.0 g of H_2O?

• A. 12.5%
• B. 0.062%
• C. 6.3%
• D. 5.9%

Answer: (D)

Verified step by step guidance

1. Identify the mass of the solute and the solvent. Here, the solute is KNO_3 with a mass of 25 g, and the solvent is H_2O with a mass of 400.0 g.
2. Calculate the total mass of the solution by adding the mass of the solute and the solvent: \(\text{mass}_{\text{solution}} = \text{mass}_{\text{solute}} + \text{mass}_{\text{solvent}}\).
3. Use the formula for percent by mass: \(\% \text{ by mass} = \left( \frac{\text{mass of solute}}{\text{mass of solution}} \right) \times 100\%\).
4. Substitute the known values into the formula: \(\% \text{ by mass} = \left( \frac{25}{25 + 400.0} \right) \times 100\%\).
5. Perform the division and multiplication to find the percent by mass of KNO_3 in the solution.