Question

Which is a Lewis acid but not a Brønsted acid? Select one: a. Fe3+ b. H3O+ c. HSO4– d. NH3 e. H2O

Answer 1

Answer : The correct option is, (a)
`Fe^(3+)`

Explanation :

According to the Bronsted Lowry concept, Bronsted Lowry-acid is a substance that donates one or more hydrogen ion in a reaction and Bronsted Lowry-base is a substance that accepts one or more hydrogen ion in a reaction.

According to the Lewis concept, an acid is defined as a substance that accepts electron pairs and base is defined as a substance which donates electron pairs.

(a)
`Fe^(3+)`

It is a Lewis-acid because it can accepts electron pairs but not a Brønsted acid because it can not donates hydrogen ion.

(b)
`H_3O^+`

It is not a Lewis-acid because it can not accepts electron pairs but a Brønsted acid because it can donates hydrogen ion.

(c)
`HSO_4^-`

It is not a Lewis-acid because it can not accepts electron pairs but a Brønsted acid because it can donates hydrogen ion.

(d)
`NH_3`

It is not a Lewis-acid because it can not accepts electron pairs but a Brønsted acid and a base because it can donates and accept hydrogen ion.

(e)
`H_2O`

It is not a Lewis-acid because it can not accepts electron pairs but a Brønsted acid and a base because it can donates and accept hydrogen ion.

Hence, the
`Fe^(3+)` is a Lewis acid but not a Brønsted acid.

Answer 2

`Fe^(3+)`

Step-by-step explanation:

Brønsted acid:-

Acids are the substances which dissociate in the aqueous medium to produce electrically charged atoms ( may be molecule). Out of these species furnished, one must be a proton or the hydrogen ion,
`H^+`.

Lewis acid:-

Compound or the ionic species that can accept electron pair from the donor compound or the ionic species.

Thus, out of the given options,
`NH_3` is a base,
`H_2O` is neutral,
`H_3O^+` and
`HSO_4^-` are Brønsted acid.

The lewis acid is :-
`Fe^(3+)`