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is the molarity is greater than molallity ??????????????

is the molarity is greater than molallity ??????????????

Grade:11

1 Answers

Aziz Alam IIT Roorkee
askIITians Faculty 232 Points
9 years ago
molarity is moles solute / litres of solution
molality is moles solute / kg solvent

For molality, you find the mass of solution, then subtract the mass of solute to get the mass of H2O
So you use a slightly lower figure for kg of water then you would litres of solution.
Thus molality will always be slightly higher.

eg
1.00 M NaCl
moles NaCl = 1.00 moles
Volume solution = 1.00 L
molarity = 1.00 M

mass NaCl in 1L 1.00 M solution = molar mass x moles = 58.44 g/mol x 1.0 moles= 58.44 g
mass H2O (assuming density = 1 g/ml) = 1000 g - 58.44 g = 941.56 g = 0.94156 kg
molality = 1.00 mol / 0.94156 kg = 1.06 m


The more dilute the solutution, the lower the mass of solute and the more similar kg solvent will be to Litres solution,
thus the more dilute the solution the closer molality and molarity will be.

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