Molality – Definition

MOLALITY IS THE MOLES OF SOLUTE IN 1 KG SOLVENT
Molality is defined as the number of moles of solute per 1 (kg) of solvent.
  • Solute = particles you dissolve
  • Solvent = the liquid you use for dissolving the particles

MOLALITY = MOLES OF SOLUTE / MASS OF SOLVENT (KG)

EXAMPLE CALCULATION
MOLALITY CARTOON

Calculate Molality of 29.8 g of glucose (C6H12O6) dissolved in 622.8 g of water

  1. Find the number of moles of sucrose

    Mass / Molar Mass = 29.8 / 180 = 0.166 moles

  2. Using formula moles/mass

    Therefore Molality = 0.166 / 0.6228 = 0.27 molal

It means there are 0.27 moles of glucose in 1 kg of water.
Molar mass of sucrose C6H12O6 = (12.01 x 6) + (1.01 x 12) + (16 x 6) = 180 g/mol

Symbol Element Atomic weight Atoms
C Carbon 12.01078 6
H Hydrogen 1.007947 12
O Oxygen 15.99943 6

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