What is the molality of a solution prepared by dissolving 12.5 g of KNO3 in 75.0 g of H2O?

• A. 2.13 mol/kg
• B. 0.213 mol/kg
• C. 0.167 mol/kg
• D. 1.67 mol/kg

Answer: (D)

Verified step by step guidance

1. Identify the formula for molality, which is defined as the number of moles of solute per kilogram of solvent: \[molality = \frac{moles\ of\ solute}{kilograms\ of\ solvent}\]
2. Calculate the moles of KNO\_3 by using its molar mass. First, find the molar mass by adding the atomic masses: K (39.10 g/mol) + N (14.01 g/mol) + 3 × O (16.00 g/mol) = 101.11 g/mol. Then, calculate moles: \[moles\ of\ KNO_3 = \frac{12.5\ g}{101.11\ g/mol}\]
3. Convert the mass of water (solvent) from grams to kilograms: \[mass\ of\ H_2O = \frac{75.0\ g}{1000} = 0.0750\ kg\]
4. Substitute the values into the molality formula: \[molality = \frac{moles\ of\ KNO_3}{0.0750\ kg}\]
5. Perform the division to find the molality in mol/kg, which will give you the concentration of the solution in terms of molality.