sodium extract

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zippy_leo:
pls tell me
a)what is the use of it in salt analysis?
b) It's given in the book that it's(sodium extract) prepared by "boiling mixture and Na2CO3 (1:3) in H2O and filtering. Filterate has soluble sodium salt of anions." What mixture are they talking of and what is this filterate, i mean from where it came?

abhishek:
sodium extract is used in popularly known test "Lassaigne's Test". It is used in salt analysis to detect nitrogen, sulphur and halogens.

Sodium extract in actual is prepared starting with sodium. It is flamed first by pressing between the folds of filter paper and then putting in ignition tube. This tube is heated very gently until sodium melts. Remove the tube from flame. Now You need to take the compound for which you are preparing the test. Put 2-3 grains of that compound if solid or 2-3 drops of liquid compound so that it comes into contact with molten sodium.  Now again the tube is slowly heated and then harshly until the tube is red hot. The red hot tube is now plunged into distilled water(~ 10 ml) in dish or beaker. Now the tube only cracks doesnt break completely. It is then crushed and boiled for 5 mins. It is then filtered which is called the sodium extract.

zippy_leo:
Thanks i got u. I actually did the same u said in XI class.
But, what happens at the end of filtering. I mean what does filterate contain? "It contains sodium sodium salt of anions" does this mean if the salt was KCl before after all this extract process it will NaCl??? Is this what it does.
And yes if it does then what's the use of it? Why cannot we apply Cl test directly? What is the use of converting into sodium salt?   

abhishek:
If making NaCl directly would have been so simple then salt would have become much much more cheaper, than it is now. It is exothermic reaction and there are more chances to accidents. So for lab purposes you need to prepare safe samples as well as reactive enough. So thats why we need to prepare sodium extract.

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