Molarity is defined as which ratio?

Molarity is defined as which ratio?

• A. M = moles solute / liters solution
• B. M = moles solute / kilograms solvent
• C. M = liters solution / moles solute
• D. M = solute mass / solution mass

Answer: (A)

Molarity is a measure of concentration defined by how many moles of solute are present in a given volume of solution. Specifically, it is the number of moles of solute divided by the volume of the entire solution in liters, so M = moles solute / liters of solution. This volume-based definition makes molarity directly useful for calculations involving volumes in solutions and reactions that occur in the liquid phase. The alternative using kilograms of solvent describes molality, not molarity. Molality uses the mass of solvent and is largely temperature-independent, which is important in some thermodynamic calculations. Dividing liters of solution by moles would give a reciprocal unit (L/mol), which is not a concentration unit. Using mass of solute per mass of solution would correspond to a mass-based concentration (like a mass fraction), not molarity. So, the defined ratio of moles of solute to liters of solution is the correct expression for molarity.

Molarity is a measure of concentration defined by how many moles of solute are present in a given volume of solution. Specifically, it is the number of moles of solute divided by the volume of the entire solution in liters, so M = moles solute / liters of solution. This volume-based definition makes molarity directly useful for calculations involving volumes in solutions and reactions that occur in the liquid phase.

The alternative using kilograms of solvent describes molality, not molarity. Molality uses the mass of solvent and is largely temperature-independent, which is important in some thermodynamic calculations.

Dividing liters of solution by moles would give a reciprocal unit (L/mol), which is not a concentration unit. Using mass of solute per mass of solution would correspond to a mass-based concentration (like a mass fraction), not molarity.

So, the defined ratio of moles of solute to liters of solution is the correct expression for molarity.