T be the boiling point of solution. The increase in

T be the boiling point of solution. The increase in the boiling point b b b  T T T is known as elevation of boiling point . Experiments have shown that for dilute solutions the elevation of boiling point ( D T b ) is directly proportional to the molal concentration of the solute in a solution. Thus D T b µ m ( . ) or D T b = K b m ( . ) Here m (molality) is the number of moles of solute dissolved in kg of solvent and the constant of proportionality, K b is called Boiling Point Elevation Constant or Molal Elevation Constant (Ebullioscopic Constant) . The unit of K b is K kg mol - . Values of K b for some common solvents are given in Table . . If w gram of solute of molar mass M is dissolved in w gram of solvent, then molality, m of the solution is given by the expression: m /M / × M ( . ) Substituting the value of molality in equation ( . ) we get D T b = b × × K M ( . ) M = b b ×  K T ( . ) Thus, in order to determine M , molar mass of the solute, known mass of solute in a known mass of the solvent is taken and D T b is determined experimentally for a known solvent whose K b value is known. g of glucose, C H O , is dissolved in kg of water in a saucepan. At what temperature will water boil at . bar? K b for water is . K kg mol - . Moles of glucose = g/ g mol – = . mol Number of kilograms of solvent = kg Thus molality of glucose solution = . mol kg - For water, change in boiling point