Answer
$AlBr_3$: Lewis acid;
$NH_3$: Lewis base;
Work Step by Step
1. Determine if each reactant can act as a Lewis base, acid or both.
- $AlBr_3$: The $Al$ is making 3 covalent bonds with the bromines, and, it has naturally 3 electrons in its valence shell, which gives us a total of 6 electrons in its valence shell. Therefore. this atom is capable of receiving 2 more electrons (To complete 8), making it a Lewis acid.
- $NH_3$: The $N$ has, naturally, 5 electrons, and it is making 3 covalent bonds with the hydrogens, leaving 2 free electrons, which the nitrogen is capable of donating. Therefore, $NH_3$ is a Lewis base.
2. So, we just have one option:
$AlBr_3$ as an acid, and $NH_3$ as a base.
