In chemistry, scaled mole conversions are used to illustrate the relationships between moles, mass, volume, and number of particles (atoms, molecules, etc.). Here are three examples of scaled mole conversions:
Example 1: Moles to Grams
Problem: Calculate the mass in grams of 3 moles of water (H₂O).
Solution:
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Determine the molar mass of water (H₂O). The molar mass is calculated as follows:
- Hydrogen (H): 1.01 g/mol × 2 = 2.02 g/mol
- Oxygen (O): 16.00 g/mol
- Total: 2.02 g/mol + 16.00 g/mol = 18.02 g/mol
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Use the number of moles to find the mass: \[ \text{Mass} = \text{Moles} \times \text{Molar Mass} \] \[ \text{Mass} = 3 , \text{mol} \times 18.02 , \text{g/mol} = 54.06 , \text{g} \]
Example 2: Grams to Moles
Problem: How many moles are in 50 grams of sodium chloride (NaCl)?
Solution:
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Calculate the molar mass of sodium chloride (NaCl):
- Sodium (Na): 22.99 g/mol
- Chlorine (Cl): 35.45 g/mol
- Total: 22.99 g/mol + 35.45 g/mol = 58.44 g/mol
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Convert grams to moles using the formula: \[ \text{Moles} = \frac{\text{Mass}}{\text{Molar Mass}} \] \[ \text{Moles} = \frac{50 , \text{g}}{58.44 , \text{g/mol}} \approx 0.855 , \text{mol} \]
Example 3: Moles to Volume (at STP)
Problem: What is the volume in liters of 2 moles of nitrogen gas (N₂) at standard temperature and pressure (STP)?
Solution:
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At STP, one mole of an ideal gas occupies 22.4 liters.
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Use the number of moles to find the volume: \[ \text{Volume} = \text{Moles} \times 22.4 , \text{L/mol} \] \[ \text{Volume} = 2 , \text{mol} \times 22.4 , \text{L/mol} = 44.8 , \text{L} \]
These examples illustrate how to perform scaled mole conversions in different contexts within chemistry.