Indicator Question (1 Viewer)

Member
I wrote that when an acid is present, it will react with the indicator, according to the equation: $\bg_white H^{+}_{(aq)} + Ind^{-}_{(aq)} \rightleftharpoons HInd_{(aq)}$, and when a base is present, it will react with the indicator, according to the equation: $\bg_white HInd^{+}_{(aq)} + OH^{-}_{(aq)} \rightleftharpoons Ind^{-}_{(aq)} + H_{2}O_{(l)}$? Would this be acceptable?

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leesh95

Member
I wrote that when an acid is present, it will react with the indicator, according to the equation: $\bg_white H^{+}_{(aq)} + Ind^{-}_{(aq)} \rightleftharpoons HInd_{(aq)}$, and when a base is present, it will react with the indicator, according to the equation: $\bg_white HInd^{+}_{(aq)} + OH^{-}_{(aq)} \rightleftharpoons Ind^{-}_{(aq)} + H2O_{(l)}$? Would this be acceptable?
This is exactly what I did. Do you get any marks for this

superSAIyan2

Member
that looks good as well. the equation vtx gave is probably best though since its more concisse

HeroicPandas

Heroic!
That question was posted up by someth1ng on the chem marathon lol

Menomaths

Exaı̸̸̸̸̸̸̸̸lted Member
That question was posted up by someth1ng on the chem marathon lol
Yeah haha

AnimeX

Member
Would i get anything if I didnt do equilibrium arrows but I did two seperate equations?

RealiseNothing

what is that?It is Cowpea
I did Ind- + H2O <> HInd + OH-

meh

darkness70

Member
I wrote that when an acid is present, it will react with the indicator, according to the equation: $\bg_white H^{+}_{(aq)} + Ind^{-}_{(aq)} \rightleftharpoons HInd_{(aq)}$, and when a base is present, it will react with the indicator, according to the equation: $\bg_white HInd^{+}_{(aq)} + OH^{-}_{(aq)} \rightleftharpoons Ind^{-}_{(aq)} + H_{2}O_{(l)}$? Would this be acceptable?
Same equation as me for the second one. I didn't write the first.
And i said when an acid is added, it removes OH- ions favouring backwards (turning indicator red) and when base is added, OH- increase and therefore favouring forwards, turning green.

Amundies

Commander-in-Chief
Did anyone write that because it shows different colours in different pH levels then it is suitable to act as an indicator? I didn't and I think that was probably worth 1 mark...

Menomaths

Exaı̸̸̸̸̸̸̸̸lted Member
Did anyone write that because it shows different colours in different pH levels then it is suitable to act as an indicator? I didn't and I think that was probably worth 1 mark...
A lot of people would've written that lol

Amundies

Commander-in-Chief
A lot of people would've written that lol
Yeah I just didn't word it properly. Not sure what I wrote but definitely not that.

Menomaths

Exaı̸̸̸̸̸̸̸̸lted Member
Yeah I just didn't word it properly. Not sure what I wrote but definitely not that.
I reckon that'd be 1 mark

Well-Known Member
i answered it with what would happen if acid/base would be added and how it would affect the equilibrium due to LCP and how a colour change would occur. Hoping for full marks for that section.

kalstar

swag
Shit will i loose marks for not putting the equilibrium arrows?

someth1ng

Retired Nov '14
Isn't it HInd + H2O <-> Ind- + H3O+

In acid, equilibrium shift to left, so colour would be same as HInd (red i think?)
In acid, use up H3O+, shift to right, Ind- colour (green?)

Neutral in middle, forgot what red + green = tho.

Is this explanation ok?
Depends on the indicator.

someth1ng

Retired Nov '14
You need to realise that all indicators have a specific pH range.

General Formula:
HInd+H2O⇌Ind-+H3O+

Indicators work because HInd and Ind- are different colours. Within the pH range of the indicator, both exist in significant quantities and hence, both have colour effects that can be seen - that's why, within a pH range, the colour appears to be a mixture of both. When outside the pH range of the indicator, equilibrium is such that either form of the indicator is significantly more dominant. Typically, a clear colour appears when one form of the indicator is approximately 10 times more concentrated than the other.

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AnimeX

Member
sai did u get overestimation or udnerestimatiom
did the question ask to calculate overestimation/underestimation?

RealiseNothing

what is that?It is Cowpea
Same equation as me for the second one. I didn't write the first.
And i said when an acid is added, it removes OH- ions favouring backwards (turning indicator red) and when base is added, OH- increase and therefore favouring forwards, turning green.

Makematics

hwpo13
I did Ind- + H2O <> HInd + OH-

meh
i did the exact same thing :O
how many marks do you reckon we can get? i said that acids would turn the indicator red, and bases would turn it green, and explained why using LCP.

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RealiseNothing

what is that?It is Cowpea
i did the exact same thing :O
how many marks do you reckon we can get? i said that acids would turn the indicator red, and bases would turn it green, and explained why using LCP.
The question said to "write an equation that involves HInd and Ind-"

We could still be right?