the molality of a solution LiF is .866m.
if its density is 1.10g/mL, what is its molarity?
im lost. how do i get mass, so i can find the moles, and the L of the solution?
Hello NeedHelp!
To find the molarity given the molality and the density:
First, since you are given the molality, let's just assume that you are working with 1 kg of water as your solvent. Use this as a conversion factor to get moles of your solute:
$\displaystyle molality (m) = \frac{moles:solute}{kg:solvent}$
1) Multiply both sides by kg to get moles.
$\displaystyle m \cdot kg = mol_{LiF} = 0.866 mols $
2) Use Molar Mass of LiF to get grams
$\displaystyle 0.866 mol \cdot \frac{25.99g}{1 mol} = 22.43 g $
3) g solute + g solvent = grams solution
$\displaystyle 1000g + 22.43g = 1022.43 g$
4) Find liters
$\displaystyle 1022.43 \cdot \frac{1 mL}{1.10g} \cdot \frac{1 L}{1000 mL} = .93 L$
5) Use your moles from #1 & your liters from #4 to get your molarity:
$\displaystyle M = \frac{mol_{LiF}}{L_{soln}} = \frac{.866 mol}{.93 L} = .932 M$
Hope that helps! Good luck!