Like water, liquid ammonia undergoes autoionization:
(a) Identify the Brønsted acids and Brønsted bases
in this reaction. (b) What species correspond to H and OH and what is the condition for a neutral solution?
H2O + HOH ==> H2O^+ + OH^-
NH3 + HNH2 ==> NH4^+ + NH2^-
NH4+ is the acid.
NH2- is the base.
Neutral solution for H2O is for H+ = OH-
Neutral soln for NH3 is for NH4+ = NH2-
To identify the Brønsted acids and Brønsted bases in the autoionization of liquid ammonia, we first need to understand the reaction itself.
The autoionization reaction of liquid ammonia (NH3) can be represented as follows:
2 NH3 ⇌ NH4+ + NH2-
In this reaction:
- The NH3 molecules act as both Brønsted acids and Brønsted bases.
- The NH4+ ion acts as a Brønsted acid.
- The NH2- ion acts as a Brønsted base.
Now, let's answer the given questions:
(a) Identifying the Brønsted acids and bases:
- Brønsted acids: In this reaction, the NH3 molecules act as both Brønsted acids and Brønsted bases. When NH3 donates a proton (H+) to another NH3 molecule, it acts as a Brønsted acid.
- Brønsted bases: The NH3 molecules also act as Brønsted bases since they can accept a proton (H+) from another NH3 molecule.
(b) Identifying the species corresponding to H and OH and the condition for a neutral solution:
- Species corresponding to H: In the autoionization of liquid ammonia, the NH4+ ion corresponds to H+. This means that when NH3 acts as a Brønsted acid, it donates a proton (H+) to another NH3 molecule, forming NH4+.
- Species corresponding to OH: In this reaction, there is no OH- ion produced. Instead, the NH2- ion corresponds to the negative charge (OH-) found in solutions of water.
- Condition for a neutral solution: A neutral solution would occur when the concentration of H+ ions (from NH4+, which acts as a Brønsted acid) is equal to the concentration of OH- ions (from NH2-, which acts as a Brønsted base). In other words, the NH3 molecules are balanced in donating and accepting protons.
To summarize, in the autoionization of liquid ammonia:
- NH3 acts as both a Brønsted acid and a Brønsted base.
- NH4+ is the species corresponding to H+.
- NH2- is the species corresponding to OH-.
- A neutral solution occurs when the concentrations of NH4+ (H+) and NH2- (OH-) are equal.