Fundamentals of Soil Science (1+1)

Exercise 10: Determination of Sesquioxides( Fe₂O₃ and Al₂O₃)

Exerise : Determination of sesquioxides( Fe₂O₃ and Al₂O₃)

Material required
Equipment and glassware

• Beaker (100ml)
• Whatman No. 40 filter paper

Reagents

• HCl
• Methyl red indicator
• Liquid Ammonia
• Ammonium nitrate (2% solution)

Procedure

• Take 50 ml of the solution A in a beaker. Add 10 ml of HCl and a few drops of methyal red indicator.
• Heat to gentle boiling and add ammonia until the precipitate is formed and the colour of the indicator just changes to distinct yellow. Boil not longer than 2 minutes and filter rapidly through a Whatman No. 40 filter paper.
• Wash the precipitate 6-8 times with hot 2% ammonium nitrate solution. Return the precipitate and filter to original beaker. Add 10 ml of HCl and macerate filter paper with a policeman. Dilute with water and heat to dissolve the precipitate. Dilute to about 20 ml and reprecipitate as directed above.
• Wash throughly with the hot ammonium nitrate solution as above until free of chlorides. Combined the first and second filterate and save them for Ca and Mg determinations.
• Ignite the precipitate gently, cool and weigh. Calculate the percentage of sesquioxide (Fe₂O₃, Al₂O₃, P₂O₅ and TiO₂ )
• If the percentage of P₂O₅ is substracted from the total remainder will be sesquioxides.

Calculations

Tare of crucible = W₁
Crucible + residue = W₂
Residue = W₂ - W₁

W₂ - W₁

= -------------------- x 100 = Y

2

Percentage of sesquioxide other than P₂O₅ = Y% P₂O₅