Gravimetric Analysis Lecture Notes

Introduction

• Titration: A method to calculate the concentration of an unknown acid or base by reacting it with a known stoichiometric amount of acid or base.
• Gravimetric Analysis: A technique where the analyte is not an acid or base but a substance that can precipitate or separate from solution.
  • Measure mass of the precipitate or analyze some aspect of the resulting system to find concentration of the analyte.
  • One of the first quantitative chemical analysis techniques.

Example

• Objective: Determine the percent by mass of magnesium sulfate in a solid mixture.

Step-by-Step Process

1. Find Mass of the Mixture:

   • Mass = 0.455 grams.

2. Dissolve in Water:

   • Add excess barium nitrate.
   • Double displacement reaction occurs, forming water-insoluble barium sulfate (precipitate).

3. Collect Precipitate:

   • Mass of precipitate = 0.6168 grams.

4. Convert Precipitate Mass to Moles:

   • Use molar mass of barium sulfate to convert mass to moles.

5. Determine Moles of Magnesium Sulfate:

   • Each sulfate in barium sulfate came from a formula unit of magnesium sulfate.
   • The number of moles of barium sulfate = number of moles of magnesium sulfate in the solution.

6. Convert Moles Back to Mass of Magnesium Sulfate:

   • Use molar mass of magnesium sulfate.
   • Resulting mass = 0.318 grams.

7. Calculate Mass Percentage:

   • (Mass of magnesium sulfate / Mass of initial solid mixture) x 100.
   • Mass percentage = 69.91%.

Conclusion

• Gravimetric analysis allows for precise determination of the component's concentration in a mixture by using precipitation reactions and mass calculations.
• In this example, it helped determine that 69.91% of the solid mixture was magnesium sulfate.