danlocke
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I remember someone in my class asking this, but I can't remember exactly what my teacher said- how do you decide whether you should use a concentrated or dilute reagent in a reaction, e.g. in the esterification of a carboxylic acid, why do we use conc. HCl?

Thanks,

Dan
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lauraMarieBrooks
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(Original post by danlocke)
I remember someone in my class asking this, but I can't remember exactly what my teacher said- how do you decide whether you should use a concentrated or dilute reagent in a reaction, e.g. in the esterification of a carboxylic acid, why do we use conc. HCl?

Thanks,

Dan
I have this problem too!


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Zygroth
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(Original post by danlocke)
I remember someone in my class asking this, but I can't remember exactly what my teacher said- how do you decide whether you should use a concentrated or dilute reagent in a reaction, e.g. in the esterification of a carboxylic acid, why do we use <b>conc.</b> HCl?<br />
<br />
Thanks,<br />
<br />
Dan
I'd guess that most of the special cases where you need to specify concentrated things are due to what's diluting it - water. In this case, the reverse reaction of an ester going back to a carboxylic acid happens with water (and is catalysed by acid) so you really want to minimise the amount of water (by using concentrated acid)
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danlocke
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(Original post by Zygroth)
I'd guess that most of the special cases where you need to specify concentrated things are due to what's diluting it - water. In this case, the reverse reaction of an ester going back to a carboxylic acid happens with water (and is catalysed by acid) so you really want to minimise the amount of water (by using concentrated acid)
Ah, that makes sense.

Thanks
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gingerbreadman85
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(Original post by Zygroth)
I'd guess that most of the special cases where you need to specify concentrated things are due to what's diluting it - water. In this case, the reverse reaction of an ester going back to a carboxylic acid happens with water (and is catalysed by acid) so you really want to minimise the amount of water (by using concentrated acid)
Or when you are looking at a reaction that is otherwise very slow. Usual cases for using conc. acids or alkalis
-esterification
-oxidation using acidified dichromate
-ester hydrolysis (saphonification)
-dehydration of alcohols
-dehalogenation of halogenoalkanes
-nitration of benzene
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username913907
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(Original post by Zygroth)
I'd guess that most of the special cases where you need to specify concentrated things are due to what's diluting it - water. In this case, the reverse reaction of an ester going back to a carboxylic acid happens with water (and is catalysed by acid) so you really want to minimise the amount of water (by using concentrated acid)

(Original post by danlocke)
Ah, that makes sense.

Thanks
NO it doesn't.

It's a catalyst for both esterification and hydrolysis.

You will need a more concentrated acid to protonate weak bases such as esters enough to have a significant rate of reaction.
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danlocke
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(Original post by JMaydom)
NO it doesn't.

It's a catalyst for both esterification and hydrolysis.

You will need a more concentrated acid to protonate weak bases such as esters enough to have a significant rate of reaction.
So the decision of what concentration to use is only determined by the desired rate of reaction?
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username913907
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(Original post by danlocke)
So the decision of what concentration to use is only determined by the desired rate of reaction?
Or the required concentration to get the reaction to occur
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danlocke
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(Original post by JMaydom)
Or the required concentration to get the reaction to occur
OK, so is it really just a case of learning what you need for each of the main reactions in the course? Or is it something you're meant to be able to deduce from a question?
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Hospes
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I had this same problem and I resolved this with myself this way. Dunno if it's right
1. Hydrolysis always requires a dilute acid or alkali because the main job is done by water.
2. A reaction which needs high concentration of protons ( deduced by the half equations) such as the reductant test by dichromate ions needs a concentrated acid.

I guess it's something to do with the mechanism, half equations and the slow rate determining step.

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username913907
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(Original post by danlocke)
OK, so is it really just a case of learning what you need for each of the main reactions in the course? Or is it something you're meant to be able to deduce from a question?
ehh, i don't know tbh. The best way is to understand the mechanics of the reactions but thats uni level
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