In: Chemistry
A 0.148-M solution of X (Mm = 177 g/mol) has a density of 1.156 g/ml. What is the molality of X in the solution?
Molarity = 0.148 = (solute weightgr/mol.wt)(1/1L)
we have mol.wt = 177g/mol
Therefore, solute weight= molarity x molecular weight
= 0.148 x
177
= 26.196
g
Weight of 1000 ml of solute = 1000 mL x density
= 1000 mL x 1.156 g/mL
= 1156 g
weight of the solvent in 1156 g of solution = 1156 g - 26.196
g
= 1129.8 g
Molality = no. moles of solute present in 1 kg (or 1000 g) of the
solvent.
therefore, molality = (Weight of Solute/Mol.
weight)(1000/solvent weight in grams)
= (26.196 g/177
g/mol)(1000/1129.8 g)
= 0.131 m
Molality of the solution = 0.131 m