GRE Subject Test: Chemistry : Lewis, Brønsted-Lowry, and Arrhenius Definitions

Example Questions

Example Question #1 : Lewis, Brønsted Lowry, And Arrhenius Definitions

What is the definition of a Brønsted-Lowry base?

A compound that donates protons in solution

A compound that accepts an electron pair in solution

A compound that donates an electron pair in solution

A compound that accepts protons in solution

A compound that accepts protons in solution

Explanation:

A Brønsted-Lowry base is any compound that accepts protons in solution. Lewis acids and bases refer to the accepting or donating of an electron pair, respectively.

Example Question #2 : Lewis, Brønsted Lowry, And Arrhenius Definitions

Acids and bases can be described in three principal ways. The Arrhenius definition is the most restrictive. It limits acids and bases to species that donate protons and hydroxide ions in solution, respectively. Examples of such acids include HCl and HBr, while KOH and NaOH are examples of bases. When in aqueous solution, these acids proceed to an equilibrium state through a dissociation reaction.

All of the bases proceed in a similar fashion.

The Brønsted-Lowry definition of an acid is a more inclusive approach. All Arrhenius acids and bases are also Brønsted-Lowry acids and bases, but the converse is not true. Brønsted-Lowry acids still reach equilibrium through the same dissociation reaction as Arrhenius acids, but the acid character is defined by different parameters. The Brønsted-Lowry definition considers bases to be hydroxide donors, like the Arrhenius definition, but also includes conjugate bases such as the A- in the above reaction. In the reverse reaction, A- accepts the proton to regenerate HA. The Brønsted-Lowry definition thus defines bases as proton acceptors, and acids as proton donors.

In the reverse reaction of , the proton is acting as a(n) __________, and is thus a __________.

electron donor . . . Lewis base

electron donor . . . Brønsted-Lowry base

electron donor . . . Lewis acid

electron acceptor . . . Lewis base

electron acceptor . . . Lewis acid

electron acceptor . . . Lewis acid

Explanation:

In terms of the passage, the lone proton can be considered a proton donor and would, therefore, be a Brønsted-Lowry acid. This is not an answer choice.

The third acid-base definition is the Lewis definition, which states that acids are electron acceptors and bases are electron donors. The negative charge on the signifies that it is a Lewis base with available electrons to donate. The proton is accepting these electrons from , and is thus acting as a Lewis acid.

Example Question #3 : Lewis, Brønsted Lowry, And Arrhenius Definitions

Which of the following molecules or ions have the greatest ability to act like a Lewis acid?

Explanation:

Lewis acids are electron pair acceptors. Molecules and ions that have a full octet cannot act a Lewis acid, therefore  and  are not lewis acids.  is very stable and insoluble and cannot accept an electron pair.  is a well known base and has extremely weak acidity.  is a transition metal ion. Transition metal are known to be Lewis acids because of their positive charge which gives them the ability to accept electron pairs.

Example Question #4 : Lewis, Brønsted Lowry, And Arrhenius Definitions

Which of the following is not a strong electrophile?

All of these are strong electrophiles.