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
Calculate Molality of 29.8 g of glucose (C6H12O6) dissolved in 622.8 g of water
-
Find the number of moles of sucrose
Mass / Molar Mass = 29.8 / 180 = 0.166 moles
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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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