What is the molality of a solution of  25g of toulene dissoved in 250g of benzene?

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Molality is a measure of concentration of a solution, expressed as moles of solute per kilogram of solvent. Toluene is the solute. It has the chemical formula C7H8 and its molar mass is 92.14 grams per mole. 

Start by calculating moles of toluene:

(25 g)(1mol/92.14 g) = 0.27 moles toluene

Now find kilograms of benzene:

(250 g)(1 kilogram/1000 grams) = 0.250 kg benzene

molality = moles toluene/kilograms benzene

molality = 0.27 moles/0.250 kg = 1.08 molal

Note that molality is not the same as molarity, which is moles solute per liter of solution. Molality is used in situations in which the temperature is likely to affect the volume of a solvent, for example when determining freezing point depression or boiling point elevation. The mass of a solvent isn't affected by temperature. 

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