Which of the following graphs best represents the relationship between the amount of solute (in moles) and the volume of solution (in liters) for a solution with constant molarity?

• A. A horizontal line above the x-axis
• B. A curve that increases exponentially
• C. A straight line passing through the origin
• D. A straight line parallel to the y-axis

Answer: (C)

Verified step by step guidance

1. Recall the definition of molarity (M), which is the concentration of a solution expressed as moles of solute per liter of solution. It is given by the formula: \[ M = \frac{\text{moles of solute}}{\text{volume of solution in liters}} \]
2. Rearrange the formula to express the moles of solute in terms of molarity and volume: \[ \text{moles of solute} = M \times \text{volume of solution} \]
3. Since the molarity (M) is constant, the relationship between moles of solute and volume is a direct proportionality, meaning the moles increase linearly as volume increases.
4. A direct proportionality between two variables is represented graphically by a straight line passing through the origin (0,0), because when the volume is zero, the moles of solute must also be zero.
5. Therefore, the graph that best represents this relationship is a straight line passing through the origin, with the slope equal to the constant molarity.