Both molarity and molality are measures of concentration, or how much solute is dissolved in solvent. Let's first get acquainted with a couple of terms.

Solute - what gets dissolved

Solvent - what the solute dissolves in

Solution - solute and solute together

Now, we can write out formulas for our two terms.

Molarity(M) = moles of solute/ Liters of solution

Molality(m) = moles of solute/ kg of solvent

As evident from the formulas, molarity and molality equations both have the same top term. However their denominators are different. For molarity calculation, we need to find liters of solution and divide by it.

For molality, we need to find kilograms of solvent.

The units for molarity are mol/L or M

The units for molality are mol/kg

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