Detection of Mg from HCl extract of Plant Ash solution

 

Detection of Magnesium in HCl extract of Plant Ash

General Test 

To detect Mg from  an unknown sample Disodium Hydrogen Phosphate test is performed.

Experiment	Observation	Inference
To about 20 ml of HCl extract of Plant Ash filtrate a drop of dil.NH4OH is added to make the solution alkaline.  The mixture is heate for 2-5 minutes and then cooled.     Finally 10% Disodium Hydrogen Phosphate is added to it.	A white ppt is formed.The ppt is of insoluble Ammonium Magnesium Phosphate.	Mg is present in the solution.

Reactions:-

MgCl2+Na2HPO4+NH4OH →Mg(NH4)PO4 (white ppt) + 2NaCl +H2O

      Or,

MgSO4+ Na2HPO4 + NH4OH → Mg(NH4)OH (white ppt) + Na2SO4 +H2O

Confirmatory Test 

Mg may be detected by the following experiments:-

  At first Ammonium Oxalate Test is performed.

Experiment	Observation	Inference
To about 20 ml of HCl extract of Plant Ash solution a drop of  dilute NH4OH is added.  then saturated Ammonium Oxalate solution is added.	A white ppt of Calcium oxalate is formed.	Ca  is present in the solution.

 

Then , Calcium oxalate is removed by filtration. With this filtrate the following test is performed:-

Experiment	Observation	Inference
The filtrate is first heated for 2-5 minutes ,then cooled. After cooling 10% Disodium Hydrogen Phosphate is added to it.	A white ppt of Ammonium Magnesium Phosphate is formed.	Mg is present in the plant Ash extract.

Reactions:-

1. Ca2+(aq) + (NH4)C2O4 (aq) →CaC2O4 (white ppt)+ 2 NH4+

2. MgCl2 + Na2HPO4 + NH4OH → Mg(NH4)PO4 (white ppt) +2 NaCl + H2O