Question

Calculate the molality of the solution. (assume a density of 1.08 g/ml for the solution.)an aqueous nacl solution is made using 140 g of nacl diluted to a total solution volume of 1.20

Answer 1

molality is moles solute / kg of solvent

 

moles of NaCl = mass / molar mass

molar mass NaCl = 58.44 g/mol

moles NaCl = 140 g / 58.44 g/mol = 2.40 mol NaCl

 

The total volume of the solution is 1.2L or 1200 ml

The density of the solution is 1.08 g/ml

 

Therefore the total mass of the solution is 1.08 g/ml x 1200 ml

= 1296 g

 

But there are140 g of NaCl in this solution

 

So mass H2O = 1296 g - 140 g

= 1156 g

= 1.156 kg

 

molality = moles solute/ kg solvent

= 2.40 mol / 1.156 kg

= 2.08 molal