Gravimetric Determination of Sulfate Content

First-Hand Investigation – Determination of the Sulfate Content (Gravimetric Determination) of a Lawn Fertiliser

Aim of Determination of the Sulfate Content of a Lawn Fertiliser
The sulfate content of ammonia fertiliser can be determined gravimetrically by converting the sulfate in a weighed sample of fertiliser to barium sulfate.
The highly insoluble barium sulfate is collected, dried and weighed of Gravimetric Determination.

    1. Dissolve 1.00 g of fertiliser in 500 mL of water in a volumetric flask.

Procedure of Determination of the Sulfate Content

    1. Transfer 100 mL of the fertiliser solution from the volumetric flask to a large beaker using a burette. Acidify with hydrochloric acid and bring to the boil.

Procedure 2

    1. Add a 5% w/w solution of barium chloride until precipitation of barium sulfate is complete.

Procedure 3

    1. Filter through a weighed filter paper. Wash the precipitate with several aliquots of hot water and dry the precipitate.

Procedure 4

    1. Reweigh the dry precipitate and filter paper. Calculate the mass of barium sulfate collected.

Procedure 5

Analysis

Analysis
0.329 g of dry barium sulfate was collected after treating 100 mL of the fertiliser solution with barium chloride.

Validity

Validity
Validity of the analysis depends on the assumptions:

  • precipitation is quantitative i.e. the filter has collected all BaSO4 particles
  • no other species present in the fertiliser are precipitated by barium ions

Accuracy

Accuracy
Can be improved by using:

  • an electronic balance rather than a beam balance
  • a fine analytical grade quantitative filter paper rather than a qualitative filter paper
  • precipitation from hot solution also helps in preventing occlusion of other species in the barium sulfate precipitate

Reliability

Reliability
Can be improved by:

  • repeating the analysis several times and averaging the results
  • precipitate must be thoroughly washed with warm water to remove any soluble species
  • then thoroughly dried in a desiccators
  • filtration must be complete otherwise the percentage of sulfate will be too low.
  • in order to achieve high accuracy, a pre-weighted filtering crucible is used so that no filter paper is needed