Chemistry A - level : H2SO4 concentrated or dilute?

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Zetnie
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Hi, I have three questions to do with H2SO4 in oxidation of alcohols:

When primary alcohols are oxidised to carboxylic acid, is the H2SO4 used dilute or conc?

When alcohols oxidised to aldehydes and ketones is the H2SO4 conc or dilute?

When aldehyde oxidised to carboxylic acid is the H2SO4 conc or dilute?

Any help is appreciated.
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Davies Chemistry
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(Original post by Zetnie)
Hi, I have three questions to do with H2SO4 in oxidation of alcohols:

When primary alcohols are oxidised to carboxylic acid, is the H2SO4 used dilute or conc?

When alcohols oxidised to aldehydes and ketones is the H2SO4 conc or dilute?

When aldehyde oxidised to carboxylic acid is the H2SO4 conc or dilute?

Any help is appreciated.
It is always dilute H2SO4 because it is in a solution (aqueous) of the oxidising agent, potassium dichromate K2Cr2O7.

Your confusion may have come from the fact that when you make up the solution of acidified potassium dichromate, sometimes it is made up by adding a few drops of conc H2SO4 into a solution of K2Cr2O7. However, the is a lot of water in the K2C2O7 solution so the resulting H2SO4 solution is dilute.

You do use conc H2SO4 in a-level organic chemistry for:
1. In electrophilic addition to alkenes - add conc H2SO4, make a sulphonated intermediate which is then reacted with water to give an alcohol.
2. Dehydration of alcohols to give alkenes
3. Mixed with conc HNO3 to make the electrophile NO2+ for reaction with benzene.
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medicnia20
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(Original post by Davies Chemistry)
It is always dilute H2SO4 because it is in a solution (aqueous) of the oxidising agent, potassium dichromate K2Cr2O7.

Your confusion may have come from the fact that when you make up the solution of acidified potassium dichromate, sometimes it is made up by adding a few drops of conc H2SO4 into a solution of K2Cr2O7. However, the is a lot of water in the K2C2O7 solution so the resulting H2SO4 solution is dilute.

You do use conc H2SO4 in a-level organic chemistry for:
1. In electrophilic addition to alkenes - add conc H2SO4, make a sulphonated intermediate which is then reacted with water to give an alcohol.
2. Dehydration of alcohols to give alkenes
3. Mixed with conc HNO3 to make the electrophile NO2+ for reaction with benzene.
Hi, for the dehydration of alcohols to form alkenes, can any concentrated strong acid be used or just H2SO4?
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Zetnie
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(Original post by Davies Chemistry)
It is always dilute H2SO4 because it is in a solution (aqueous) of the oxidising agent, potassium dichromate K2Cr2O7.

Your confusion may have come from the fact that when you make up the solution of acidified potassium dichromate, sometimes it is made up by adding a few drops of conc H2SO4 into a solution of K2Cr2O7. However, the is a lot of water in the K2C2O7 solution so the resulting H2SO4 solution is dilute.

You do use conc H2SO4 in a-level organic chemistry for:
1. In electrophilic addition to alkenes - add conc H2SO4, make a sulphonated intermediate which is then reacted with water to give an alcohol.
2. Dehydration of alcohols to give alkenes
3. Mixed with conc HNO3 to make the electrophile NO2+ for reaction with benzene.
Thanks for this great explanation that has really helped me a ton.
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Zetnie
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(Original post by Davies Chemistry)
It is always dilute H2SO4 because it is in a solution (aqueous) of the oxidising agent, potassium dichromate K2Cr2O7.

Your confusion may have come from the fact that when you make up the solution of acidified potassium dichromate, sometimes it is made up by adding a few drops of conc H2SO4 into a solution of K2Cr2O7. However, the is a lot of water in the K2C2O7 solution so the resulting H2SO4 solution is dilute.

You do use conc H2SO4 in a-level organic chemistry for:
1. In electrophilic addition to alkenes - add conc H2SO4, make a sulphonated intermediate which is then reacted with water to give an alcohol.
2. Dehydration of alcohols to give alkenes
3. Mixed with conc HNO3 to make the electrophile NO2+ for reaction with benzene.
Also, do you also use concentrated H2SO4 for esterification
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cefox
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(Original post by medicnia20)
Hi, for the dehydration of alcohols to form alkenes, can any concentrated strong acid be used or just H2SO4?
You can also use concentrated phosphoric acid for this reaction...it also acts as a dehydrating agent.
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cefox
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(Original post by Zetnie)
Also, do you also use concentrated H2SO4 for esterification
Yes, usually you do.
This acts as a catalyst so doesn’t appear in the main equation for the reaction.
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Zetnie
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(Original post by cefox)
Yes, usually you do.
This acts as a catalyst so doesn’t appear in the main equation for the reaction.
ok thanks!
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