Aniline, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\), is a weak base, with a lone pair of electrons on the nitrogen atom. (a) According to Bronsted and Lowry, what must aniline do to act as a base? (b) Why can aniline act as a base? (c) What are the molecular formula and charge of the conjugate acid of aniline?

Understanding the nature of bases in chemistry is crucial for grasping various reactions. A Bronsted-Lowry base is a substance that accepts a proton, which is a hydrogen ion (( H^+ )). This model of acid-base reaction was proposed by Johannes Bronsted and Thomas Lowry, who redefined bases along these lines. An easy way to remember this is that bases 'befriend' protons by providing them a place to dock, which is usually on a negatively charged site or a lone pair of electrons present in the base.

Take aniline, for instance. As a weak base, it demonstrates the Bronsted-Lowry concept by having the capacity to accept a proton. This acceptance is due to the presence of a reactive site which in aniline's case, is the nitrogen atom's lone pair of electrons.

In an acid-base reaction, it's essential to recognize not just the initial reactants but also the products formed. A conjugate acid is the species formed when a base gains a proton. It's essential to see this as a family affair – the base and its conjugate acid are closely related, the only difference between them being one proton. During a reaction, a base transforms into its conjugate acid by accepting a proton.( H^+ ).

The relation between aniline and its conjugate acid is a classic example. When aniline, acting as a base, accepts a proton, it changes its identity slightly to become the conjugate acid, displaying a positive charge to account for the new proton in the family.

A lone pair of electrons refers to a pair of valence electrons that are not involved in bonding but instead belong exclusively to one atom. These electrons are like the 'unused potential' of an atom that can lead to chemical reactions involving the formation of new bonds. The presence of a lone pair on an atom allows it to act as a Lewis base in reactions by offering these electrons to bond with other atoms or ions.

In the case of aniline, the nitrogen atom holds this lone pair, making it ready and able to bond with an incoming proton. Picture these electrons as outstretched hands, ready to shake hands with a new friend (the proton) to form the conjugate acid.

To better understand reactions, knowing the participants' 'names' (or molecular formulas) is essential. The molecular formula of the conjugate acid of a base gives us specifics about the number of atoms of each element in the conjugate acid molecule. It's a chemical shorthand that tells us how many of each type of atom we're dealing with after the base has accepted a proton.

With aniline, once it embraces a proton, it becomes ( C_6H_5NH_3^+ ). We've added one hydrogen to the count and tacked on a positive charge to indicate the proton's addition. Understanding this new molecular formula is key to recognizing how aniline interacts in its environment post-reaction, now as a conjugate acid.