Relating mole fraction and molality

What is the mole fraction of glycine molecules in 0.140 m NH2CH2COOH(aq) Disregard the effects of protonation 

Strategy We consider a sample that contains (exactly) 

1 kg of solvent and hence an amount j = fej X (1 kg) of solute molecules. The amount of solvent molecules in exactly 1 kg of solvent is 

Molality is typically reported in moles of solute per kilogram of solvent (mol kg ). This unit is sometimes (but unofficially) denoted m, with 1 m = 1 mol kg . An important distinction between molar concentration and molality is that whereas the former is defined in terms of the volume of the solution, the molality is defined in terms of the mass of solvent used to prepare the solution. A distinction to remember is that molar concentration varies with temperature as the solution expands and contracts, but the molality does not. For dilute solutions in water, the numerical values of the molality and molar concentration differ very little because 1 dm of solution is mostly water and has a mass close to 1 kg for concentrated aqueous solutions and for all nonaqueous solutions with densities different from 1 g cm , the two values are very different. 

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