The residue left after the burning of coal is known as ash. It is generally composed of inorganic substances. The total sulphur content of coal can be determined gravimetrically by the Eschka method. In this method, a coal sample is heated with the Eschka mixture (2:1 calcined magnesia and anhydrous sodium carbonate by weight) in an oxidizing atmosphere. This removes majorly all combustible matter and converts all forms of sulphur (pyritic’ and ‘organic, sulphur) to sulphate

1. SHREE MALLIKARJUN COLLEGE CLASS:SYBSC
SAFETY: Refer to MSDS of charcoal, barium chloride, hydrochloric acid, sodium carbonate, magnesium carbonate, magnesia
-Dr. Mithil S. FalDesai
Aim: Determination of sulphur and ash content in the sample of Coal/Charcoal.
Chemicals: Charcoal, barium chloride, hydrochloric acid, sodium carbonate, magnesium carbonate/
magnesia
Apparatus/Instrument: Standard volumetric flask, beakers, funnel, measuring cylinder, dropper, crucible.
Theory: The residue left after burning of coal is known as ash. It is generally composed of inorganic
substances. The total sulphur content of coal can be determined gravimetrically by Eschka method. In
this method, a coal sample is heated with the Eschka mixture (2:1 calcined magnesia and anhydrous
sodium carbonate by weight) in an oxidizing atmosphere. This removes majorly all combustible matter
and converts all forms of sulphur (pyritic’ and ‘organic, sulphur) to sulphate.
Procedure: A) Determination of ash content
1) Weigh 1 g of coal is weighed in a previously weighed silica crucible.
2) Crucible is heated in a muffle furnace at 800°C for 2 h. (disturb while heating.)
3) After incineration, cool the crucible and keep in a desiccator for 1 h.
4) Crucible is weighed and ash content is determined.
B) Determination of sulphur content
1) Weigh 1 g of coal is weighed in a silica crucible.
2) Add and mix 1 g of Na2CO3 and 2 g of MgO (Eschka mixture) in the crucible.
3) Crucible is heated in a muffle furnace at 800 °C for 2 h.
4) Cool the crucible and add 10 mL of 2N HCl and transfer the content in a beaker.
5) Filter the content and transfer in 50 mL standard flask and dilute up to the mark.
6) Pipette out 10 mL of the solution and add 10 mL of 10% BaCl2 solution to the beaker.
7) Keep the white precipitate for 20 min on the water bath for digestion.
4) Cool the precipitate and filter through ash-less filter paper.
8) Wash the precipitate with cold distilled water until filtrate is free from chloride ions.
9) Transfer the precipitate along with filter paper in a previously weighed silica crucible and heat it at 900
◦C.
10) Cool it and keep it in a desiccator for 15 min and weigh the precipitate as BaSO4.
Results: i) % of ash (inorganic residue) =____%
ii) i) % of Sulphur (total) =____%
Further reading
1) Experiments in Applied Chemistry, S. Rattan, S. K Kataria, and Sons.
Questions.
1) What are the different forms of sulphur present in charcoal?
2) Why calcine magnesia is used in Eschka mixture.
3) Why sulphuric acid is not used to dissolve the residue?
4) Can you use nitric acid for dissolving the residue?
5) What is ash?
6) How you can determine the presence of barium in the ash?
7) Name any one naturally occurring ore of sulphur.