I'm trying to reach a more thorough understanding of what's going on when we calculate equilibrium concentrations and was wanting to understand more what assumptions we make in order to follow through with the calculations.(adsbygoogle = window.adsbygoogle || []).push({});

Let me ask off of an example:

Consider mixing equal amounts of NH3 and HCl, each having the concentration ofαupon mixing.

The general way I've seen taught is to assume via being a strong acid that the HCl fully ionizes and causes the following equation to occur:

NH3 + H30^{+}→ NH4^{+}+ H2O

Then to recognize that NH4^{+}is a weak acid, so we'll need to set up the reverse equation as an equilibrium to run an ICE problem off of:

NH4^{+}+ H2O ←→ NH3 + H30^{+}

Wherein we take the initial concentration of NH4^{+}to beα, and can use it's K_{a}to find the final hydrogen ion concentration of the entire solution.

Here then are my questions directly:

1) In the first equation, we seem to assume that all the hydrogen ions from HCl jump onto our NH3, thus allowing us to use our initial α concentration also as the initial concentration of NH4^{+}. How so? Could it not be that some hydrogen ions tend to stick around as H30^{+}, thereby reducing the actual concentration of NH4^{+}to slightly less thanα? What knowledge/assumptions do we use to reduce this complexity from our calculations?

2) Are there any other important assumptions we make when working similar equilibrium problems? As I work them myself, I constantly feel like the scenarios are a bit oversimplified (even if I acknowledge they give us answers very proximal to reality).

Thanks much!

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# Assumptions Built in to Solving Titration Equilibria?

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