When a solution is diluted by adding more solvent, how does this process affect the molarity of the solution?

• A. Dilution does not affect the molarity.
• B. Dilution increases the molarity directly.
• C. Dilution increases the molarity indirectly.
• D. Dilution decreases the molarity directly.

Answer: (D)

Verified step by step guidance

1. Understand that molarity (M) is defined as the number of moles of solute divided by the volume of the solution in liters, expressed as \(M = \frac{\text{moles of solute}}{\text{volume of solution (L)}}\).
2. Recognize that when you dilute a solution by adding more solvent, the number of moles of solute remains constant because no solute is added or removed.
3. Note that the volume of the solution increases because more solvent is added, which means the denominator in the molarity expression increases.
4. Since the numerator (moles of solute) stays the same and the denominator (volume) increases, the overall molarity decreases.
5. Therefore, dilution directly decreases the molarity of the solution because molarity is inversely proportional to the volume when moles of solute are constant.