Sulphate Gravimetric Analysis Virtual Lab

Theoretical Background/Context

• Gravimetric analysis of sulphate is a quantitative method for accurately determining the amount of a substance by selective precipitation of the substance from an aqueous solution. 
• The precipitate is separated from the remaining aqueous solution by filtration and is then weighed.
• The principle behind the gravimetric analysis is that the mass of an ion in a pure compound can be determined and then used to find the mass percent of the same ion in a known quantity of an impure compound.

In order for the analysis to be accurate, certain conditions must be met:

1. The ion being analyzed must be completely precipitated.
2. The precipitate must be a pure compound.
3. The precipitate must be crystalline and easily filtered.

The steps of gravimetric analysis include:

1. Precipitation

1. Colloidal ppt.

•  Tiny particles pass through filter paper.
•  Show no tendency to settle from a solution.

2. Amorphous ppt.

• Large surface area.
• Aggregates of nuclei easily transform into the colloidal state.

3. Crystalline ppt.

• Particles with large size.
• Tend to settle spontaneously.
• Easily washed and retained on the filter paper.

Obtained by precipitation from hot dilute solution with stirring and adding the precipitating agent slowly dropwise.

2. Ageing (crystal growth):

• This happens when a freshly formed precipitate is left in the solution from which it precipitates.
• It results in cleaner and bigger particles.

3. Filtration

• Done by decantation or using ash-less filter paper.

4. Washing

• To remove surface adsorbed impurities

5. Drying  ( < 250 oC ) Or Ignition ( > 250oC -1200oC).

6. Weighing

7. Calculation

Principle of Work

• In the Sulphate Gravimetric Analysis Virtual Lab, you will determine the percentage (by mass) of sulfate in an unknown sulfate salt by gravimetric analysis. 
• In BaSO₄ gravimetric analysis, sulfate salt is precipitated by barium chloride as barium sulphate. 
• After filtration and drying the precipitate, calculations should be made to determine the percent of sulphate in the sample.