To solve a mass-mass stoichiometry problem, you need to convert the mass of a given substance to the mass of a different substance in the same chemical equation. Here's a step-by-step approach, incorporating information from the provided video reference:
Steps to Solve Mass-Mass Stoichiometry Problems
The core process involves converting between mass and moles, utilizing molar masses and mole ratios from a balanced chemical equation.
1. Start with the Given Mass
- You begin with the mass of a substance that's part of a balanced chemical equation.
2. Convert Mass to Moles
- Find the molar mass: Determine the molar mass of the substance using the periodic table.
- Convert to moles: Divide the given mass by its molar mass to convert it into moles. The video explains, "You would find the molar mass of that substance. And use that to convert to moles of the substance."
3. Use the Mole Ratio
- Identify the mole ratio: From the balanced chemical equation, determine the mole ratio between the given substance and the substance you're trying to find.
- Convert to moles of the target substance: Multiply the moles of the given substance by the mole ratio to find the moles of the target substance.
4. Convert Moles back to Mass
- Find the molar mass: Find the molar mass of the target substance.
- Convert to mass: Multiply the moles of the target substance by its molar mass to convert it into grams of the target substance.
Summary Table
| Step | Action | Conversion |
|---|---|---|
| 1 | Start with the known mass (grams) | Given mass in grams |
| 2 | Convert mass to moles using the molar mass of the known substance | Mass (g) / Molar mass (g/mol) = Moles |
| 3 | Use the mole ratio from the balanced equation | Moles of Known * (Moles of Unknown / Moles of Known) |
| 4 | Convert moles of target substance to mass of the target substance | Moles * Molar mass (g/mol) = Mass (g) |
Example
Let’s say you have a balanced chemical equation: 2H₂ + O₂ → 2H₂O
- If you’re given 4 grams of hydrogen (H₂) and want to find how many grams of water (H₂O) will be produced:
- Given Mass: Start with 4 grams of H₂.
- Mass to Moles: Molar mass of H₂ is approximately 2 g/mol. So, 4 g / 2 g/mol = 2 moles of H₂
- Mole Ratio: The ratio from the equation is 2 moles H₂ : 2 moles H₂O, which simplifies to 1:1. Therefore, 2 moles of H₂ produces 2 moles of H₂O
- Moles to Mass: Molar mass of H₂O is approximately 18 g/mol. So, 2 moles * 18 g/mol = 36 grams of H₂O.
Therefore, 4 grams of hydrogen will produce 36 grams of water.
Key Takeaways
- Mass-mass stoichiometry problems always involve converting between grams and moles.
- The mole ratio from the balanced chemical equation is crucial for relating different substances.
- Pay close attention to units and ensure they cancel correctly.
By following these steps, you can successfully solve mass-mass relationship problems in stoichiometry.
