[Amine]

I recently did a titration in which I titrated sodium hydroxide and an excess of sodium chloride solution into a conical flask containing a known volume and concentration of hydrochloric acid, in order to find an average titre. The indicator we used was methyl orange.

I am just wondering why do the sodium chloride not effect the titre?

May you please explain to me why?
Thanks in advance!

[Hunter2]

The hydrochloric acid  react with sodiumhydroxide to which product? Then you can explain by yourself.

[Amine]

Yes the product is NaCl, and this causes the change in indicator colour. But I am unsure as to why the colour does not change in the first place because the NaOH solution contains excess NaCl also.

[Hunter2]

Thats wrong. The sodiumchloride dont change the colour of indicator. What else could it be what will change the colour.

[Amine]

Well we are adding NaOH, so is it this which changes the colour, because it is neutralising the acid?

[Hunter2]

You have 99 points. To get 100 point describe what happens at neutralisation. What is the main point of it?

[Amine]

Water is produced?

[Hunter2]

Yes and where does this water comes from. What is really changed in the solution?

[Amine]

The hydroxide ion from NaOH and the hydrogen ion from HCl.

[Hunter2]

Yeah . The indicator shows the amount of H⁺ or OH^- with one of his colour. At neutralisation this number is very low and the colour changes. So now you can answer your question by yourself.

[Amine]

Because the excess NaCl does not contribute any H⁺ ions and therefore does not affect the colour change and nor the neutralisation reaction.

[Hunter2]

Yeahhhh, you got it.

[Borek]

In other words: indicator reacts to pH changes.

[Hunter2]

Probably on that level the TES dont know pH. But you are right thats the answer.