Lecture Notes on Calculating Mass from Moles
Introduction
- Objective: To calculate the mass needed for a given number of moles of a compound.
- Reference to previous lesson: Calculation of the number of moles from a given mass.
Key Formula
Example 1: Sodium Chloride (NaCl)
- Problem: Calculate the mass of 4 moles of sodium chloride.
- Steps to Solve:
- Calculate the relative formula mass of NaCl:
- Na (Sodium) = 23
- Cl (Chlorine) = 35.5
- Total = 58.5
- Use the formula:
- Mass = 4 moles ( \times ) 58.5
- Result = 234 grams
Practice Question 1: Potassium Oxide (K2O)
- Problem: Calculate the mass of 3 moles of potassium oxide.
- Given:
- K (Potassium) = 39
- O (Oxygen) = 16
- Solution Steps:
- Compute relative formula mass:
- 2 Potassium atoms: 2 ( \times ) 39 = 78
- 1 Oxygen atom: 1 ( \times ) 16 = 16
- Total = 94
- Calculate mass:
- Mass = 3 moles ( \times ) 94
- Result = 282 grams
Practice Question 2: Cesium Nitrate (CsNO3)
- Problem: Calculate the mass of 0.1 moles of cesium nitrate.
- Given:
- Cs (Cesium) = 133
- N (Nitrogen) = 14
- O (Oxygen) = 16
- Solution Steps:
- Compute relative formula mass:
- Cs = 133
- N = 14
- O = 3 ( \times ) 16 = 48
- Total = 195
- Calculate mass:
- Mass = 0.1 moles ( \times ) 195
- Result = 19.5 grams
Practice Question 3: Copper Sulfate (CuSO4)
- Problem: Calculate the mass of 5 moles of copper sulfate.
- Given:
- Cu (Copper) = 63.5
- S (Sulfur) = 32
- O (Oxygen) = 16
- Solution Steps:
- Compute relative formula mass:
- Cu = 63.5
- S = 32
- O = 4 ( \times ) 16 = 64
- Total = 159.5
- Calculate mass:
- Mass = 5 moles ( \times ) 159.5
- Result = 797.5 grams
Conclusion
- Additional resources available in the vision workbook for more practice.
- Goal: Understanding and ability to calculate the mass needed for any given number of moles of a compound.
Note: The relative formula masses and atomic masses are crucial for these calculations.