use this equation

.. dTbp = kb * m * i

where

.. dTbp = change in bp = bp solution - bp pure solvent

.. kb = ebullioscopic constant (boiling point elevation constant) for the solvent

... .m = molality = moles solute / kg solvent

.. . i = van't hoff factor = # ions 1 particle dissociates into in solution

examples of i

.. 1 NaCl ---> 1 Na+ + 1 Cl-... 1 particle ---> 2 ions... i=2

.. 1 MgCl2 --> 1 Mg2+ + 2 Cl-... 1 particle --> 3 ions.. i=3

.. 1 glucose ---> 1 glucose.. glucose doesn't dissociate.. 1 particle --> 1 particle... i=1

and..

.. since like dissolves like.. non-polar solvents dissolve non-polar solutes and non-polar solutes don't usually

.. .. . .... dissociate. So IF the solvent is non-polar, assume i=1

.. anything that dissolves in water and doesn't dissociate.. assume i=1

.. non-electrolytes means the species doesn't dissociate... i=1

.. non-volatile means it stays in solution.

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that out of the way... do this

.. (1) rearrange dTbp = kb * m * i.... to solve for "m"

.. (2) use the results from (1) along with the kg of H2O to solve for moles solute

.. (3) molar mass = mass / mole

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and if you still need help..

.. m = (100.635°C - 100.000°C) / (0.512°C/m * 1) = 1.240m.. ... (3 sig figs + 1 extra for intermediate calcs)

.. 0.2006 kg H2O * (1.240 mol solute / 1kg H2O) = 0.2487 mol solute... (3 sig figs)

.. molar mass solute = 14.96g / 0.2487mol = 60.2 g/mol... .(3 sig figs)