Why is it necessary to convert the concentration from mg/L to molarity in chemical calculations?

• A. Molarity is always a larger value than mg/L, making calculations easier.
• B. Converting to molarity eliminates the need to know the molar mass of the solute.
• C. Molarity expresses concentration in terms of moles of solute per liter, which is required for stoichiometric calculations.
• D. Molarity is used only for solutions containing gases.

Answer: (C)

Verified step by step guidance

1. Understand that concentration can be expressed in different units, such as mg/L (mass per volume) or molarity (moles per liter).
2. Recognize that chemical reactions and stoichiometric calculations are based on the number of moles of substances involved, not just their mass.
3. Recall that molarity (M) is defined as the number of moles of solute divided by the volume of solution in liters: \(M = \frac{\text{moles of solute}}{\text{liters of solution}}\).
4. To convert from mg/L to molarity, you need to use the molar mass of the solute to convert mass (mg) to moles: \(\text{moles} = \frac{\text{mass (mg)}}{\text{molar mass (mg/mol)}}\).
5. Therefore, converting concentration to molarity is necessary because it expresses the amount of solute in moles, which is essential for accurate stoichiometric calculations in chemical reactions.