Mass Fraction: The mass fraction of a component in a mixture is the ratio of the mass of that component to the total mass of the mixture. It is used when dealing with processes that focus on the weight or mass of substances, such as in engineering or industrial chemistry.
Mole Fraction: The mole fraction of a component in a mixture is the ratio of the number of moles of that component to the total number of moles of all components in the mixture. It is common in chemical thermodynamics and reactions, as it provides information about the number of particles (molecules, atoms) involved, which is important for stoichiometric calculations.
1. Mass Fraction Example:
Suppose you have a mixture containing:
- 20 g of ethanol (C₂H₅OH)
- 80 g of water (H₂O)
- Total mass of the mixture = 20 g (ethanol) + 80 g (water) = 100 g
The mass fraction of ethanol = 20/100 = 0.2
The mass fraction of water = 80/100 = 0.8
This means 20% of the mass of the mixture is ethanol, and 80% is water.
2. Mole Fraction Example:
Using the same mixture with 20 g of ethanol and 80 g of water, we calculate the moles for each component.
- Molar mass of ethanol (C₂H₅OH) = 46.07 g/mol
- Molar mass of water (H₂O) = 18.02 g/mol
The number of moles of ethanol = 20/46.07 = 0.434 mol
The number of moles of water = 80/18.02 = 4.44 mol
Now, the total number of moles = 0.434 mol (ethanol) + 4.44 mol (water) = 4.874 mol
The mole fraction of ethanol = 0.434/4.874 = 0.089
The mole fraction of water = 4.44/4.874 = 0.911
This means that 8.9% of the moles in the mixture are ethanol molecules, and 91.1% are water molecules.
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