Hi;
I'm just wondering, I need to write the dissocation equation for NH3 so that I can get Kb, and I just want to make sure that I am on the write track. I know that when some solids dissociate they just go from say CaCO3 --> CaO + CO2, but for this I'm wondering because it's a base it would be NH3 +H20 --> NH4+ + OH- or if it would still be NH3 --> NH2 + H2 ...
There are compounds, such as NaNH2 (sodamide) that have the negative ion, NH2^-) but you are right on track.
NH3 + HOH ==> NH4^+ + OH^-
Do you want to know a little of the history of this? When I took my first chemistry course, we were taught that
NH3 + HOH ==> produced NH4OH, and the NH4OH dissociated as follows:
NH4OH ==> NH4^+ + OH^-. But research has shown now that there is no NH4OH produced and the reaction procedes directly from NH3 to NH4^+ + OH^-. That intermediate of NH4OH was necessary in order to explain by the Arrhenius theory why NH3 was a base; i.e., NH4OH contained an OH part and that was the base. With the Bronsted-Lowry theory, however, no such intermediate is required. I think the Arrhenius theory still is useful; however, most texts now emphasize the Bronsted-Lowry theory initially.
Hi! It seems like you are trying to determine the dissociation equation for ammonia (NH3) in order to calculate its base dissociation constant (Kb).
You're correct in recognizing that when solids dissociate, they usually break up into simpler components. However, for ammonia, which is a weak base, it undergoes a different type of dissociation in water.
The dissociation equation for ammonia in water is NH3 + H2O ⇌ NH4+ + OH-. This equation shows that when ammonia reacts with water, it forms ammonium ions (NH4+) and hydroxide ions (OH-).
The arrows in the equation represent a reversible reaction, indicating that the products can react back to reform the reactants. This is because in water, some of the ammonia molecules will accept a hydrogen ion (H+) from water to form NH4+ ions, while some of the water molecules will donate a hydroxide ion (OH-) through the removal of a hydrogen ion (H+).
To calculate the base dissociation constant (Kb) for ammonia, you will need to use equilibrium expressions and the concentrations of the reactants and products. Kb is a measure of the strength of a base. It is calculated by taking the concentration of the products (NH4+ and OH-) and dividing it by the concentration of the reactants (NH3).
I hope this clarifies your understanding of the dissociation equation for ammonia (NH3) and its base dissociation constant (Kb). If you have any further questions, feel free to ask!