Molarity vs. molality - 4 | Chemical Calculations for Solutions
General Chemistry 2 - Molarity vs. molality - 4
A concentrated sodium hydroxide solution is 30.0% NaOH by mass and has a density of 1.325 g.mL-1 at 25°C.
Calculate the molarity of this solution.
mass% = x 100
⇒ in the solution, there are 30.0 g of NaOH in 100 g of solution
Step 1: determine the mass of NaOH mNaOH in one liter of solution:
mNaOH (in g) = V (in mL) x d (in g.mL-1) x = 1000 x 1.325 x 0.300 = 397.5 g
Step 2: determine the molarity of the solution:
nNaOH = and nNaOH = Msol x Vsol
⇒ Msol x Vsol =
⇒ Msol (in mol.L-1) = = = 9.94 mol.L-1