Video: Atoms and Structure

Two aqueous complex ions react according to the equation: [Cu(H₂O)₅(OH)]⁺ + [Al(H₂O)₆]³⁺ ⟶ [Cu(H₂O)₆]²⁺ + [Al(H₂O)₅(OH)]²⁺. (a) Which species is the Brønsted-Lowry acid in this reaction? (b) Which species is the conjugate base of the Brønsted-Lowry acid? (c) Which species is the Brønsted-Lowry base of this reaction? (d) Which species is the conjugate acid of the Brønsted-Lowry base in this reaction?

03:29

Video Transcript

Two aqueous complex ions react according to the equation. Which species is the Brønsted-Lowry acid in this reaction?

In the equation, we have a copper complex reacting with an aluminum complex. And some form of exchange is occurring between their ligands. And we form two different complexes. The question asks us to identify the Brønsted-Lowry acid. So, we should go back to the definition of a Brønsted-Lowry acid.

Commonly, if something is called an acid, it’s likely to be a Brønsted-Lowry acid. A Brønsted-Lowry acid is a substance that does or can lose protons in a reaction. This is what a reaction might look like. An acid molecule with a proton interacts with a base and donates its proton. So, the question is, in the reaction we’ve been given, which component is acting as a Brønsted-Lowry acid?

Let’s have a look at the copper ion pair. The product, the hexaaquacopper(II) cation, has one extra proton than the pentaaquahydroxocopper(II) cation. The hydroxo ligand gains a proton, forming the sixth aqua ligand. Meanwhile, the hexaaquaaluminum ion loses a proton to form pentaaquahydroxoaluminum(III). Now that we know which species loses a proton, we can express it in this form. And we know that the Brønsted-Lowry acid in this reaction is the hexaaquaaluminum(III) cation.

Which species is the conjugate base of the Brønsted-Lowry acid?

In the context of a Brønsted-Lowry acid, a conjugate base is a substance that is or can be formed by the loss of protons from a Brønsted-Lowry acid. The species in this reaction that is formed by loss of a proton is the pentaaquahydroxoaluminum(III) cation. So, this is the conjugate base of our Brønsted-Lowry acid.

Which species is the Brønsted-Lowry base of this reaction?

The definition of a Brønsted-Lowry base is a substance that does or can gain protons in a reaction. We already know from part a that the pentaaquahydroxocopper(II) cation gains a proton during the reaction. So, this is our Brønsted-Lowry base.

Which species is the conjugate acid of the Brønsted-Lowry base in this reaction?

In the context of a Brønsted-Lowry base, a conjugate acid is a substance that is or can be formed by the gaining of protons by a Brønsted-Lowry base. The hexaaquacopper(II) cation is formed by the gaining of a proton in this reaction. So, this is our conjugate acid.

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy.