A solution of salt water raised the boiling point of water from 100 degrees celsuis to 107.5 degrees celsius. What is the molality of the solution?

Question

I need help on this i do not get it at all..............................

 

Answer 1

This is a problem concerned with raising the boiling point of water by the addition of a solute.  This is a colligative property and obeys the equation:

 

∆T = imK

∆T = change in temperature

i = van't Hoff factor = 2 for NaCl (Na⁺ and C^-)

m = molality (moles solute/kg solvent)

K = boiling point constant = 0.512 deg/m

 

7.5 deg = (2)(m)(0.512)

m = 7.5 deg/(2)(0.512 deg/m)

m = 7.32 molal