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Question 29

Calculate the molarity of a solution of ethanol in water in which the mole fraction of ethanol is 0.040 (assume the density of water to be one).


Mole fraction of C2H5OH=   .................1

Let the moles of C2H5OH= X

Now density of water = 1 (given)

And the weight of 1000ml of water = volume * density (from density = mass/volume)

= 1000 x 1=1000g

Therefore moles of water = 1000/18= 55.55 mol (18g is molecular mass of water)

Also mole fraction of C2H5OH= 0.040 (given)

Putting the values in equation 1,we get


=0.040X+2.222 = X

OR X= 2.3145 mol

Molarity of solution = 2.314 M



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