[vivekrai]

In Sodium Fusion test, Why is an excess of Sodium is used?

[Arkcon]

I could look it up for you, but you'll learn more if your figure it out for yourself.  (That is in fact, this site's policy, check the Forum Rules, in red above.)  To begin to solve it yourself:  What does the Sodium Fusion test for?  What reaction is involved?  Generally, we use an excess of reagent for a few reasons, have you come up with any of those reasons before?

[Jasim]

How do you know what excess is in this case? It is an elemental analysis after all, so assuming you are doing the test because you don't know what's there.

[Arkcon]

Jasim: if you look up a typical Sodium-fusion Test, also called Lassaigne Test, you might have an insight on how you can be sure the sodium is in great access.  FWIW, I'd never even heard of this test, much less done it, but a quick Google search and Wikipedia read later, it seems pretty clear to me, at least from the standpoint of the OP's question.  But this is one crazy procedure to follow, from what I read online.

[Borek]

I'd never even heard of this test, much less done it

It was an obligatory part of an organic lab I did back in early eighties.

[Arkcon]

I'd never even heard of this test, much less done it

It was an obligatory part of an organic lab I did back in early eighties.

Really.  That is pretty far out there.  Consider -- you start with an organic compound, you react it elemental sodium (!), but then, you perform inorganic chemistry on the solution formed to analyze, qualitatively, C, N, S, and halides.  Seems more like an inorganic chemistry experiment -- and a pretty advanced one.

[vivekrai]

What does the Sodium Fusion test for?  What reaction is involved?  Generally, we use an excess of reagent for a few reasons, have you come up with any of those reasons before?

Excess because so that all of the organic compound that we are supposed to add is converted into the corresponding ionic species?

[Borek]

Excess because so that all of the organic compound that we are supposed to add is converted into the corresponding ionic species?

Yes, thsi way you can be sure whatever tests you do later, your organic compound doesn't interfere.

[Jasim]

Other than the prohibitive costs of MS, is there a reason such a test would be performed? Perhaps when dealing with completely new compounds?

Let me clarify, my rationale is that if you want the structure of an unknown substance MS (or even NMR) is the way to go. Correct me if I'm wrong.

[Borek]

This is an old test, it was a basic step in analysis long before spectroscopy of any kind became a routine. Whether it makes sense to use it or not depends on what kind of lab/hardware you have at hand. Sodium and test tubes are much easier to find than MS or NMR machine.

[vivekrai]

Yes, We can't hunt for a NMR machine is a small school lab.