Which statement concerning solution concentration is true?

• A. Molarity is defined as the number of moles of solute per liter of solution.
• B. A saturated solution always contains more solute than an unsaturated solution at the same temperature.
• C. Percent by mass is calculated as the mass of solute divided by the volume of solution, multiplied by 100%.
• D. Molality is defined as the number of moles of solute per liter of solution.

Answer: (A)

Verified step by step guidance

1. Review the definitions of common concentration units: molarity, molality, and percent by mass.
2. Recall that molarity (M) is defined as the number of moles of solute divided by the volume of the solution in liters, expressed as \(M = \frac{\text{moles of solute}}{\text{liters of solution}}\).
3. Understand that molality (m) is defined as the number of moles of solute divided by the mass of the solvent in kilograms, expressed as \(m = \frac{\text{moles of solute}}{\text{kilograms of solvent}}\).
4. Recognize that percent by mass is calculated as the mass of solute divided by the total mass of the solution, multiplied by 100%, expressed as \(\% \text{ by mass} = \frac{\text{mass of solute}}{\text{mass of solution}} \times 100\%\).
5. Evaluate the statements given in the problem by comparing them to these definitions to identify which one is true.