Question

If the density of methanol is 0.793 kg L–1, what is its volume needed for making 2.5 L of its 0.25 M solution?

Answer 1

Solution: We know that

The molarity of a solution is defined as  M = number of moles of solute/ Volume of solution (in litres)   = (mass of solute/ molar mass of solute)X (1/ Volume of solution (in litres)

Let x g of methanol (molar mass = 32g) be required to prepare a 0.25 Molar solution of methanol. 

Therefore we have  0.25 = (x/32) X (1/2.5)  

x = 20g = 0.02 Kg

Now density = Mass/ Volume 

We are given that the density of methanol is 0.793 KgL^-1. 

Therefore,   Volume = Mass/ Density  = 0.02/0.793  = 0.025 Litres

Therefore 0.025 Litres of methanol would be required.