[~charmaine~]

This is going to sound really stupid but can water act as both acid and base? Its just that in a revision guide, it says " Hydrolysis with aqueous acid to produce...." and the equation is "CH3C00C2H5 +H2O-----> CH3COOH+ C2H5OH"

[SmilerNuts]

Yes, it's amphoteric (sp?).

[cpchem]

Water is able to act as both acid and base, yes, either forming a hydroxide if acting as an acid, or oxonium if base.
That reaction though? Hydrolysis of ethyl acetate by water? It won't happen - you need harsher conditions to hydrolyse an ester.

[~charmaine~]

So when the book say aqueous acid, does it actually mean water?

[PoisonDonna]

Yes it can be both.

2 H2O(l) <---> H3O+(aq) + OH-(aq)

It depends on conditions where the equilibrium lies, and hence whether water acts as an acid or a base.

[originalname]

Yep, water can form both hydroxide (OH-) and oxonium (H3O+).

In the first case it acts as a Bronst-Lowry acid, donating H+, in the second, a base accepting H+.

[PoisonDonna]

Originally Posted by ~charmaine~

So when the book say aqueous acid, does it actually mean water?

It means acid diluted in water. So you will have acid ions present and the water ions.

[originalname]

Originally Posted by ~charmaine~

So when the book say aqueous acid, does it actually mean water?

No, hydrolysis of an ester needs concentrated acid or base as a catalyst.

"Acid hydrolysis/ base hydrolysis of an ester."

I.e. CH3COOC2H5 + H2O, in the presence of concentrated HCl, CH3COOH + C2H5OH

Or

CH3COOC2H5 + H2O, in the presence of concentration NaOH, CH3COO- + C2H5OH

[~charmaine~]

I am just kinda confused. here's the whole thing from the revision guide

Hydrolysis with aqueous acid to produce the organic acid and the alcohol
CH3COOC2H5 + H2O <====> CH3COOH + C2H5OH
Condition: heat under reflux with dilute sulphuric acid

Hydrolysis with aqueous alkali to produce the salt of the acid and the alcohol
CH3COOC2H5 +NaOH ------> CH3COONa + C2H5OH
Condition: heat under reflux with aqueous sodium hydroxide

Why aqueous acid is water and aqueous alkali id sodium hydroxide???

[Rob801]

Originally Posted by ~charmaine~

Why aqueous acid is water and aqueous alkali id sodium hydroxide???

aqueous acid is referring to the dilute sulphuric acid (ie. an acid dissolved in water).

aqueous alkali is referring to the aqueous sodium hydroxide (ie. a base dissolved in water).

edit: the reason the first reaction only mentions the water is because the acid ions are spectator ions and therefore are left out of the equation. the second one has the NaOH in the equation because the sodium ion is used to form one of the products (a carboxylic acid is formed, but then reacts with the NaOH to form the sodium salt).

[charco]

The equation that appears to be confusing people is an equilibrium.

CH3COOC2H5 + H2O <==> CH3COOH + C2H5OH

As this is an equilibrium it can (and does) go both ways. In the forward direction the reaction is very very slow at room temperature, but it can be speeded up by using an acid (or base) catalyst (it may still take up to a week to establish equilibrium at room temp). The H+ ions are therefore a catalyst, and the forward reaction can be considered to be hydrolysis of the ester.

It will still only reach equilibrium (and not go all the way to the products) and if my memory serves me well the equilibrium constant is about 4 (dont quote me on this! I can't remember if this is the equilibrium constant for the forward or the reverse reaction, but in either case it's pretty close to 1), and if so there is about twice as much of the products as reactants at equilibrium at room temperature.

The reverse reaction also occurs (almost) equally slowly at room temperature in the presence of dilute acid or base. (remember the condition for equiliibrium is that the forward and reverse reactions proceed at the same rate at equilibrium)

However, the reason for carrying out the reverse reaction is usually to prepare a sample of ester.

In this case concentrated acid is used as it can then serve the dual purpose of catalysing the reaction AND removing water from the equilibrium, pulling the equilibrium to the left hand side and producing more ester.

[lahiru]

what happen when we put NaOH to this ,CH3COCl + C2H5OH --> CH3COOC2H5 + HCl