Results are out! Find what you need...fast. Get quick advice or join the chat
x

Unlock these great extras with your FREE membership

  • One-on-one advice about results day and Clearing
  • Free access to our personal statement wizard
  • Customise TSR to suit how you want to use it

Acid-base indicators: what does "end-point colour" mean?

Announcements Posted on
Find your uni forum to get talking to other applicants, existing students and your future course-mates 27-07-2015
Win top prizes in our mega results day giveaway... 24-07-2015
  1. Offline

    ReputationRep:
    Example:

    Phenolphthalein
    Colour in acid: colourless
    Colour in alkali: purple
    End-point colour: pale pink

    Methyl orange
    Colour in acid: red
    Colour in alkali: yellow
    End-point colour: orange
  2. Offline

    ReputationRep:
    (Original post by Alpha-Omega)
    Example:

    Phenolphthalein
    Colour in acid: colourless
    Colour in alkali: purple
    End-point colour: pale pink

    Methyl orange
    Colour in acid: red
    Colour in alkali: yellow
    End-point colour: orange
    When the acid/base have been neutralised.
  3. Offline

    ReputationRep:
    (Original post by thegodofgod)
    When the acid/base have been neutralised.
    Is it when the pH is 7 (neutral)?


    Or is it the colour change that we're looking for during acid-base titration?
  4. Offline

    ReputationRep:
    (Original post by Alpha-Omega)
    Is it the colour change that we're looking for during acid-base titration?

    Or is it when the pH is 7 (neutral)?
    No, as GOG says it is the point when exactly all of the acid has been neutralised by the correct amount of base (or vice versa)

    If you have chosen the correct indicator you will also see the colour change here. It is NOT pH 7 (unless you have strong acid and strong base)
  5. Offline

    ReputationRep:
    (Original post by charco)
    No, as GOG says it is the point when exactly all of the acid has been neutralised by the correct amount of base (or vice versa)

    If you have chosen the correct indicator you will also see the colour change here. It is NOT pH 7 (unless you have strong acid and strong base)
    Is the given end-point colour (e.g., pale pink for phenolphthalein) only true for an acid titrant? or is it also the same for a base titrant?

    Edit: I've done a bit of googling, does the end-point colour show when the concentration of the unionised indicator is equal to the concentration of ionised indicator?


  6. Offline

    ReputationRep:
    (Original post by Alpha-Omega)
    Is the given end-point colour (e.g., pale pink for phenolphthalein) only true for an acid titrant? or is it also the same for a base titrant?

    Edit: I've done a bit of googling, does the end-point colour show when the concentration of the unionised indicator is equal to the concentration of ionised indicator?

    Yes, but don't forget that in titration there is such a radical change of pH with tiny additions near the endpoint that it is virtually impossible to assure that you are exactly at the endpoint.

    For example, with phenolphthalein titrating a base with an acid, you would look for the colour disappearing.

    The other way round and you look for the colour appearing (the first permanent hint of pink).

    Hence the equal concentration of both indicator forms being equal in concentration is a theoretical concept that is pretty unlikely in practise.

Reply

Submit reply

Register

Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. By joining you agree to our Ts and Cs, privacy policy and site rules

  2. Slide to join now Processing…

Updated: January 8, 2012
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

Poll
Do you think you'll do better or worse than your predicted grades?
New on TSR

Results are coming...

No sweat. Here's all you need to make sure you're ready

Study resources
x

Think you'll be in clearing or adjustment?

Hear direct from unis that want to talk to you

Get email alerts for university course places that match your subjects and grades. Just let us know what you're studying.

Quick reply
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.