9. Carboxylic Acids and Derivatives
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What is the functional group of carboxylic acids?
R - COOH
Are carboxylic acids weak or strong acids?
Weak
Why do carboxylic acids not fully dissociate in water?
As they are weak acids
What equations can be used to show how carboxylic acids do not fully dissociate in water?
• R-COOH + H2O ⇋ RCOO- + H3O⁺ * R-COOH ⇋ R-COO- + H⁺
How is a proton released in the equation R-COOH ⇋ R-COO- + H⁺?
The polarised C=O group attracts electrons away from the O-H group, weakening the OH bond enabling the proton to be released
Why do carboxylic acids dissociate in water, but alcohols do not?
In the carboxylic acid OH group the C=O group attracts electrons away, weakening the OH bond so a proton can be released - but there is no C=O group in an alcohol so there is nothing to weaken the OH bond
What are carboxylic acids produced by?
The oxidation of primary alcohols or aldehydes
What happens when ethanol is exposed to air?
It oxidises to ethanoic acid
Why can wine taste vinegary if left open?
The ethanol oxidises to ethanoic acid
Where is methanoic acid found naturally?
In an ant bite; it can cause irritation
Where is ethanedioic acid found naturally?
As a metal salt in rhubarb and gives it a sour taste
What is ethanedioic acid?
A poisonous white crystalline solid
Where is benzene carboxylic acid (benzoic acid) found?
Raspberries and some tree barks
How is benzoic acid used?
As a preservative and an antioxidant in numerous foods
How are carboxylic acids named?
Using the suffix -oic acid
What do carboxylic acids react with alkalis to form?
Water and carboxylate salts
In the reaction of carboxylic acids with alkalis, what happens in terms of hydrogen ions?
The acid donates a hydrogen ion (from -COOH) which is replaced by the metal in the alkali
Equation for ethanoic acid with sodium hydroxide?
CH3COOH + NaOH → CH3COONa + H2O
In the products from carboxylic acids with alkalis, what is the nature of the bond between the carboxylate ion and the metal?
Ionic
How are carboxylate salts named?
The prefix is the name of the metal and the suffix is -oate instead of -oic acid
What do carboxylic acids react with carbonates and hydrogen carbonates to form?
Salt, water and carbon dioxide
Are carbonates and hydrogen carbonates weak or strong bases?
Weak
What is a general equation for the reaction of carboxylic acids with sodium carbonates?
R-COOH + Na2CO3 → RCOO⁻⁻Na⁺ + CO2 + H2O
What is a general equation for the reaction of carboxylic acids with sodium hydrogencarbonates?
R-COOH + NaHCO3 → RCOO⁻⁻Na⁺ + CO2 + H2O