Ammonium hydroxide is commonly advertised as an ingredient in some window cleaners. Rank the following in order of decreasing concentrations in these solutions:
NH4OH, NH4+, OH-, NH3.
Explain your reasoning. (Note that kb for ammonia = 1.8 x 10^-5.
So does an unionized ion have a higher concentration?
Is the answer:
NH4OH > NH3> NH4+>OH- ?
To rank the following species in order of decreasing concentrations in window cleaners, we need to consider their relative ionization and equilibrium in solution.
First, let's break down the species:
1. NH4OH: This is ammonium hydroxide, which can be considered a weak base. In solution, it dissociates into NH4+ (ammonium ion) and OH- (hydroxide ion).
2. NH4+: This is the ammonium ion, a positively charged ion.
3. OH-: This is the hydroxide ion, a negatively charged ion.
4. NH3: This is ammonia, which is the unionized form of ammonium hydroxide.
Next, let's consider the equilibrium reaction for NH4OH in solution:
NH4OH ⇌ NH4+ + OH-
In this reaction, NH4OH can dissociate into NH4+ and OH- ions. However, since NH4OH is a weak base, it does not completely dissociate.
To determine the concentrations, we need to compare the relative amounts of NH4+ and OH- ions formed from the dissociation, as well as the concentration of un-ionized NH4OH. This can be done using the equilibrium constant (Kb) for ammonia:
Kb = [NH4+][OH-] / [NH4OH]
Given that Kb for ammonia is 1.8 x 10^-5, we can conclude that the concentrations of NH4+ and OH- ions are much smaller than that of NH4OH.
Based on this information, the correct ranking, from highest to lowest concentration, is:
NH4OH > NH4+ > NH3 > OH-
Explanation:
- NH4OH has the highest concentration as it is the undissociated form of ammonium hydroxide. Although it partially dissociates, the concentration of NH4OH is greater than the concentration of its dissociated ions.
- NH4+ has the next highest concentration as it is formed from the dissociation of NH4OH. However, the concentration of NH4+ is smaller than that of NH4OH due to the incomplete dissociation.
- NH3 (ammonia) is the unionized form of NH4OH, so its concentration will be lower compared to NH4+.
- OH- has the lowest concentration as it is formed from the dissociation of NH4OH, but its concentration is smaller compared to NH4+ due to the incomplete dissociation.
So, the correct ranking is: NH4OH > NH4+ > NH3 > OH-.
I'm not sure how to answer this question. Technically there is no such compound as NH4OH and I hope your prof is teaching you that. Based on that being zero, then
NH3 > NH4^+ = OH^- > NH4OH = 0
What this should tell you is that the the NH3 gas dissolves in the solvent and when it ionizes (it's a weak base--look at the Kb) it produes small amount of NH4^+ and an equal amount of OH^-. Most of the NH3 stays as NH3 gas dissolved in the solvent.