If you are provided with 2.5M NaOH solution having density 1.5g/mL, then find the molality of solution.
A
1.17m
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B
1.79m
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C
2.27m
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D
2.47m
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Solution
The correct option is B1.79m 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
Mass of NaOH (Solute) = moles×molarmass=2.5×40=100g,
Also density of solution =mass of solution (g)Volume of solution (mL)=1.5g/mL
Mass of solution = 1500g.
Mass of solution = mass of solute + mass of solvent
1500 = 100 + Mass of solvent
Mass of solvent = 1400 g = 1.4 kg
Hence,molality(m)=moles of soluteweight of solvent(kg) =2.51.4=1.79m