elevation of boiling point the boiling point of a liquid is the temperature at which it's vapor pressure becomes equal to atmospheric pressure that is 760 mm of hedgy consider a common example we all know that water boils at hundred degrees Celsius but if we dissolve some sugar in it the boiling point of the solution increases from hundred degrees Celsius to hundred and two degrees Celsius now let us understand why addition of a non-volatile solute to a pure solvent increases the boiling point of the solution the addition of a non-volatile solute lowers the vapor pressure of the solvent the vapor pressure of the solution is always lower than that of the pure solvent from roult's law hence the solution must be heated to in higher temperature to make its vapor pressure equal to atmospheric pressure we can conclude that the boiling point of the solution is higher in comparison to that of the pure solvent now let us clearly understand this concept using a graph let us plot a graph of vapor pressure versus temperature if we notice the graph we can observe that vapor pressure of the solvent is always higher than vapor pressure of the solution at a particular temperature thus the solution boils at a higher temperature than the pure solvent if T not B is the boiling point of the solvent and TB is the boiling point of the solution the difference in boiling points is called the elevation of boiling point it is represented as Delta TB thus TB minus T not B is equal to Delta TB if we increase the concentration of the solute in the solution we can observe that the solution curve shifts downwards further increasing the difference in boiling points thus we can infer that Delta TB is directly proportional to molarity of the solution this implies that the elevation in boiling point of a dilute solution is directly proportional to the number of moles of the solute hence the number of particles dissolved in a given mass of the solvent expressed in kg and it is independent of the nature of the solute hence elevation of boiling point is a colligative property Delta TB is equal to KB into M where KB is a molar elevation constant also called as a Bulow scopic constant and M as molarity of the solution determination of molar mass of solute from elevation in boiling point temperature the elevation in boiling point can be used in determining the molar mass of the solute in order to calculate the molar mass of an unknown non volatile compound a known amount of it as the salt in a known mass of some suitable solvent an elevation in boiling point is determined let W be gram of non-volatile solute B dissolved in W a grams of the solvent and M B is the molar mass of the solute therefore the molality M of the solution is moles of solute in 2000 by weight of solvent in grams when moles of solute is equal to weight of the solute WB by molar mass of the solute M be molarity of the solution M is equal to weight of the solute WB in 2000 by molar mass of the solute M be into weight of solvent W a elevation in boiling point Delta TB is equal to mole al elevation in boiling point KB into molarity of the solution M Delta TB is equal to KB into weight of solute WB in 2000 by Delta TB into weight of solvent W a from this relation molar mass of the solute can be calculated knowing the values of other quantities