Equilibrium and indicator equation

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    Equilibrium
In summary, the equilibrium will move to the right as the [In-] concentration increases. This is because the reaction will try to minimize the effect of the change, and so In- will be increased.
  • #1
haha0p1
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The equation for indicator is:
HIn ⇌H+ + In-
Which reaction (forward or reverse) will be preferred when I increase the Alkali.
According to me, The reverse reaction should be preferred as the reaction will try to minimize the effect of the change. Hence In- (i.e the conjugate base) will be increased as it will react with H+ to form HIn.
But the coursebook says that the position of the equilibrium will move to the right. Kindly explain why is that so?
 

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  • #2
How would the reverse reaction minimise the effect of the change?
How is [In-] increased by reacting with H+?
 
  • #3
Not enough information to answer. Alkali what? Alkali salt? Alkali base?
 
  • #4
haha0p1 said:
The equation for indicator is:
HIn ⇌H+ + In-
Which reaction (forward or reverse) will be preferred when I increase the Alkali.
According to me, The reverse reaction should be preferred as the reaction will try to minimize the effect of the change. Hence In- (i.e the conjugate base) will be increased as it will react with H+ to form HIn.
But the coursebook says that the position of the equilibrium will move to the right. Kindly explain why is that so?
The question should be in the homework section. I think it is a good question, deserving some attention by chemistry teachers. I think when I first met this subject at school I felt confused, the reason being what I saw as ambiguous expressions like "the equilibrium will move to the right" I was thinking of equilibrium as weights on a lever… but never mind.

Help yourself by writing out the equation for the equilibrium constant relating [HIn] to the dissociation products molarities [H+] and [In-]. "Adding alkali" means adding something like NaOH, I.e. essentially adding OH- to the solution, which will react with H+ there, and directly or indirectly with HIn (it matters not which) to do - what? So think again through what will happen – you have got it wrong.

I think it is better to work out your own way of thinking and talking about these things (which you are likely to meet again again) rather than someone else's way of expressing it.
 

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