Carboxylic acids

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1

Carboxylic acid functional group:

Has the structure -COOH

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Dicarboxylic acids contain 2 -COOH groups

Ethanedioic acid: HOOC-COOH

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BOILING and MELTING points of carboxylic acids:

Simple aliphatic carboxylic acids (not aromatic) are liquid at room temperature.
But the BOILING POINTS are even higher than alcohols

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Reason for REALLY HIGH boiling points:

Can form hydrigen bonds due to a hydrogen being bonded to an oxygen, however the O-H bond is more polar than in alcohols due to the adjacent C=O group so *stronger hydrogen bonds form*
There structure also allows *more hydrogen bonds* to be formed as they can form dimers.

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Dimers

Dimers are pairs of molecules bonded together, they each contain two hydrogen bonds in the case of carboxylic acids

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Other intermolecular forces in carboxylic acids:

Van der Waals forces can also be formed, this means larger molecules with more electrons/more surface area form stronger vdw's

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Smaller molecules solubility:

Small carboxylic acids are completely miscible with water as can form hydrogen bonds with the water

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Larger molecules solubility:

As the size of the carboxylic acids carbon chain increases the molecule gets less soluble as the rest of the molecule is non polar and cannot form hydrogen bonds so cannot dissolve.

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PREPARATION of carboxylic acids:

Oxidation of a primary alcohol OR an aldehyde produces a carboxylic acid.
Conditions: React with Hot Aqueous Acidic Potassium Dichromate under REFLUX!

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ALL reactions of carboxylic acids depend on...

THE FACT THAT IT IS AN ACID... so reacts with bases or reactive metals to form salts (in the same way inorganic acids do)

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Base:

A base is a species that can accept a proton

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Acid metal reaction:

Carb acid + metal → Salt + hydrogen gas

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Acid carbonate reaction:

Carb acid +carbonate → Salt + carbon dioxide + water

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Acid ammonia reaction:

Carb acid +ammonia → Ammonium salt

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Acid base reaction (KOH)

Carb acid + base → Salt + water

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Esterification:

Carb acid + alcohol → Ester + water