Question

Vanilla is an olfactory indicator. It looses it's pleasant smell when a base is added to it. So, my question is, what happens when we first add base to vanilla extract and then add acid to the solution. Will it regain it's smell?

Answer 1

Answer:

That will depend on How much acid you put in.

Ok, let me explain.

First you took around 5moles of NaOH, you added the vanilla extract, and observed loss of smell. Well and good.

Now, I took an acid, lets take HCl, but I was short of it and I took 3 moles.

Look at the reaction below,

$NaOH+ HCl$ → $NaCl + H_{2} O$

You must be familiar with it, it is the Neutralization reaction.

This reaction states, 1 mole of NaOH reacts with 1 mole of HCl to form 1 mole of NaCl and 1 mole of water.

So, If I add 3moles of HCl in 5 moles NaOH only 3 moles of NaOH shall be neutralised. All HCl is used up and we are left with excess 2 moles of NaOH. Sadly, my Vanilla smell does not come back.

Now I called my chemical supplier to bring 5 moles of HCl, to put in the Vanilla+ 5 mole NaOH solution. Now, with this all the NaOH reacts to form Salt and water! My pleasant smell of Vanilla comes back!

But, since I'm careless I inverted 5 moles of HCl in the beaker which had 2moles of NaOH left, (the first experiment where I added 3 mole HCl in5 mole NaOH, to give 3 mole of salt and water). But, no worries, Vanilla Smell persists even after excess of acid remaining in the solution!

So, what do we learn by this experiment?

You must put the acid just enough to either to neutralise the base or make the pH acidic.

That's why I said, It would depend on how much Acid to put into.

Kudos!