If you are provided with a 2.5M NaOH solution having a density of 1.6g/mL, then find the molality of solution. (Atomic mass of Na=23g)
A
1.17m
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B
1.66m
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C
2.27m
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D
2.47m
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Solution
The correct option is B1.66m Molarity(M)=Moles of soluteVolume of solution (L) Let us assume volume of solution to be 1 litre or 1000mL. Hence moles of NaOH = Molarity of solution = 2.5moles Again, molar mass of NaOH=23+16+1=40g Mass of NaOH (Solute) = moles×molarmass=2.5×40=100g, Also the density of the solution =mass of solution (g)Volume of solution (mL)=1.6g/mL Mass of solution = 1600g. Mass of solution = mass of solute + mass of solvent 1600 = 100 + Mass of solvent Mass of solvent = 1500 g = 1.5 kg Hence,molality(m)=moles of soluteweight of solvent(kg) =2.51.5=1.66m