Which of the following expressions correctly defines the molarity (M) of a solution?
Answer
M = \frac{\text{mass of solute (g)}}{\text{molar mass (g \; mol^{-1})} \times \text{volume of solution (L)}}
The correct answer is M = \frac{\text{mass of solute (g)}}{\text{molar mass (g \; mol^{-1})} \times \text{volume of solution (L)}} — Check each option: option (a) matches the derived expression; the others miss a factor or use incorrect units.
Step-by-step solution
- Recall that molarity is defined as the number of moles of solute per litre of solution.
- The number of moles of solute is obtained by dividing the mass of solute (in grams) by its molar mass (g \; ).
- Thus, M = \frac{\text{mass (g)}}{\text{molar mass (g \; mol^{-1})}} \times \frac{1}{\text{volume (L)}} = \frac{\text{mass of solute}}{\text{molar mass} \times \text{volume of solution}}.
- Check each option: option (a) matches the derived expression; the others miss a factor or use incorrect units.
Common mistake: Confusing molarity with molality or using volume in mL instead of L.
Concept tested: Definition of molarity
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