Derived formula of molarity is equal to

• A. (g/L) / molecular weight
• B. (moles/L) * 2
• C. (grams/L) * molecular weight
• D. (L/g) / MW

Answer: (A)

Molarity is defined as the number of moles of solute per liter of solution. If you know the mass concentration (grams per liter) and the molecular weight (grams per mole) of the solute, you can convert to molarity by dividing the mass concentration by the molecular weight. This works because moles = mass ÷ molar mass, and then you still divide by the volume in liters, giving M = (g/L) ÷ (g/mol) = mol/L.

So the correct expression is grams per liter divided by the molecular weight, since MW is in g/mol. Units check out too: (g/L) ÷ (g/mol) simplifies to mol/L. For example, if a solute has 36 g/L and a molecular weight of 180 g/mol, the molarity would be 36/180 = 0.2 mol/L.

The other forms don’t match the units or the definition: multiplying by 2 would only be correct if you had extra information, multiplying grams per liter by the molecular weight gives a unit that isn’t molarity, and using L/g divided by MW yields an incorrect unit as well.