Scaled conversions in chemistry often involve converting between different units of measurement, such as moles, grams, liters, or other quantities. Here are three examples that are appropriate for 10th-grade chemistry:
Example 1: Moles to Grams
Problem: Convert 2.5 moles of NaCl (sodium chloride) to grams.
Solution:
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Find the molar mass of NaCl:
- Sodium (Na) = 22.99 g/mol
- Chlorine (Cl) = 35.45 g/mol
- Molar mass of NaCl = 22.99 + 35.45 = 58.44 g/mol
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Use the conversion factor: \[ \text{Mass (g)} = \text{Moles} \times \text{Molar Mass} \] \[ \text{Mass} = 2.5 , \text{moles} \times 58.44 , \text{g/mol} = 146.1 , \text{g} \]
Example 2: Liters to Moles (using molarity)
Problem: How many moles of NaOH (sodium hydroxide) are present in 3.0 liters of a 0.50 M solution?
Solution:
- Use the molarity formula: \[ \text{Molarity (M)} = \frac{\text{Moles of solute}}{\text{Liters of solution}} \]
- Rearrange the formula to solve for moles: \[ \text{Moles} = \text{Molarity} \times \text{Volume (L)} \] \[ \text{Moles} = 0.50 , \text{M} \times 3.0 , \text{L} = 1.5 , \text{moles} \]
Example 3: Grams to Moles
Problem: Convert 100 grams of CO₂ (carbon dioxide) to moles.
Solution:
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Find the molar mass of CO₂:
- Carbon (C) = 12.01 g/mol
- Oxygen (O) = 16.00 g/mol
- Molar mass of CO₂ = 12.01 + (2 × 16.00) = 44.01 g/mol
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Use the conversion factor: \[ \text{Moles} = \frac{\text{Mass (g)}}{\text{Molar Mass (g/mol)}} \] \[ \text{Moles} = \frac{100 , \text{g}}{44.01 , \text{g/mol}} \approx 2.27 , \text{moles} \]
These examples illustrate how to perform scaled conversions between moles, grams, and liters in a chemistry context.
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