If 15.0 g ethyl alcohol (CH3CH2OH) are dissolved in 500 g water, find the molality of the solution?
Answer:
Let ethyl alcohol be called EA. Mol. wt. EA = 46
15.0gEA/500gH2O x 1molEA/46gEA x 1000g/1kg = 0.65 mol EA per kg H2O
which is molality.
first you should get the number of moles of ethyl alcohol
15/46 = 0.326
then divide it by wight of the solvent in Kg
you get 0.326/0.5 = 0.652 m
The molar mass of ethyl alcohol is 46.079. Therefore 15g will contain 15/46.079 moles of ethyl alcohol which is equal to 0.3255 moles. 500g of water is 500 mL so there are 0.3255 moles of ethyl alcohol in half a litre henc there will be twice as much in one litre which equals 0.651moles.
The molarity of te solution is thus 0.651M
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