How many grams of KNO_3 (formula weight 101.1 g/mol) are required to prepare 1.00 L of a solution containing 125 mg/L of nitrogen (N)?

• A. 1.26 g
• B. 0.125 g
• C. 0.225 g
• D. 0.505 g

Answer: (C)

Verified step by step guidance

1. Identify the given information: the solution volume is 1.00 L, and the nitrogen concentration is 125 mg/L. The formula weight of KNO_3 is 101.1 g/mol.
2. Convert the nitrogen concentration from mg/L to grams per liter: 125 mg/L = 0.125 g/L. Since the solution volume is 1.00 L, the total mass of nitrogen in the solution is 0.125 g.
3. Calculate the moles of nitrogen present using its atomic mass (approximately 14.0 g/mol): moles of N = mass of N / atomic mass of N = 0.125 g / 14.0 g/mol.
4. Determine the moles of KNO_3 needed. Since each formula unit of KNO_3 contains one nitrogen atom, moles of KNO_3 = moles of N.
5. Calculate the mass of KNO_3 required using its molar mass: mass of KNO_3 = moles of KNO_3 × 101.1 g/mol.