We have 1L of 0.1mol/l solution of ammonium chloride, with pKa 9.2 for NH4+/NH3
Place in an increasing order on a pKa axis the different conjugate acid /base pairs present in the solution.
Write the equation of the different reactions that may take place
dH rxn = (n*dHo products) - (n*dHo reactants)
To determine the different conjugate acid/base pairs present in the solution and write their reactions, we need to understand the acid-base behavior of ammonium chloride (NH4Cl) and its components.
The ammonium chloride (NH4Cl) solution contains two main species: ammonium ion (NH4+) and chloride ion (Cl-). We consider NH4+ as the acid, which can donate a proton (H+) to form its conjugate base, ammonia (NH3). On the other hand, Cl- is considered a spectator ion as it does not participate in acid-base reactions.
First, let's determine the pKa value for the NH4+/NH3 system. The pKa is the negative logarithm of the acid dissociation constant (Ka), and it represents the tendency of an acid to donate a proton. Since we know that pKa(NH4+/NH3) = 9.2, we can conclude that the conjugate acid/base reaction is as follows:
NH4+ ⇌ NH3 + H+
Now, let's consider the different reactions that can occur in the solution:
1. NH4+ ⇌ NH3 + H+
This reaction represents the dissociation of the ammonium ion (NH4+) into ammonia (NH3) and a proton (H+). This is an acid dissociation reaction.
2. NH3 + H2O ⇌ NH4+ + OH-
In this reaction, ammonia (NH3) acts as a base and reacts with water (H2O) to form ammonium ion (NH4+) and hydroxide ion (OH-). This is an example of base-catalyzed hydrolysis.
3. NH4+ + H2O ⇌ NH3 + H3O+
Here, the ammonium ion (NH4+) reacts with water (H2O) to yield ammonia (NH3) and hydronium ion (H3O+). This is the reverse reaction of reaction 2 and represents an acid-base reaction.
4. Cl- (spectator ion)
As mentioned earlier, chloride ion (Cl-) does not participate in any acid-base reactions in this system.
Finally, let's arrange the conjugate acid/base pairs in increasing order of their pKa values:
1. NH4+/NH3 (pKa = 9.2)
To summarize, the ammonium chloride (NH4Cl) solution contains the NH4+/NH3 conjugate acid/base pair. The reactions that may occur include the dissociation of NH4+ into NH3 and H+, the hydrolysis of NH3 with water to form NH4+ and OH-, and the reaction of NH4+ with water to produce NH3 and H3O+.