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Calculating Equilibrium Concentrations And Ph From Ka

Trent You

1. Synopsis:

This ChemWiki page begins with an introduction of a typical acidic dissociation equation, and describes how to write a Ka formula based on it with Ka = [Products]/[Reactants]. Next, it describes how to find the concentration of hydrogen ions from the pH with [H3O+] = 10-pH. The author then procedes with five examples. The first example involves finding the pH of the weak acid HOBr with a given Ka this involved using ICE tables and a demonstration of the quadratic formula. Next, the author gives another example with a weak acid and a given Ka, but this time requiring just the concentration of hydrogen ions, this again required ICE tables and the quadratic formula. The third example looks for the amount of the weak acid, benzoic acid, at equilibrium, involving the ICE table and the Ka, with a subtraction of the amount of hydrogen ions in equilibrium from the initial concentration of benzoic acid. The fourth example is similar to the third, given a weak acid and a Ka value; it required all equilibrium values, not just the hydrogen ion concentration or the undissolved acid concentration. Finally, the fifth example uses the equilibrium concentrations from example four and requires the pH value of each concentration.

2. Review Details

Content:

It works well that the main content of your wiki page is made up of examples, as it is easier to learn from. However, all of your examples involve weak acids, which may not be representative of what professors might provide on a test. There may be strong acids, weak bases, or strong bases that we may need to find the pH of from the Ka. It might be helpful to explain how to determine Kb from Ka and to use that to determine equilibrium concentrations of a basic equation. Perhaps before each example you could explain what the example entails, and the point you are attempting to teach in it.

In the introduction "General Guide to Solving Problems involving Ka", as a reader who does not understand Ka, it would help if you explained what ICE is and what "x" means. It is only after the reader scrolls down to the examples that he or she will understand the steps. Also, it might be better to place the "How to write the Ka formula" before the "General Guide to Solving Problems involving Ka", as the progression makes more sense to know what Ka actually is before solving problems with Ka.

Formatting errors:

The page guideline that contains the links to each section of the wiki has many errors, as section 1.4 simply has a long underline. Also, section 5.1 is also simply an underline. The section numbers should start at 1, rather than 1.1. You also need to use the subscript and superscript buttons on the top of the page, as opposed to writing Ka or 10^(-pH). However, the sections in which you used an image to write a chemical equation works very well and should be used more often. Your quadratic equations are also extremely clear due to the use of an image rather than regular text. Furthermore, I believe the ice tables were a good choice in explaining ice tables and are quite effective in describing change from an initial state to equilibrium; mirroring the formal in which professors generally teach.

Example #5:

I believe the fifth example is confusing, as you ask for the pH of all the molecular concentrations in the solution. The concentration of the weak acid HOCl does not actually contribute to the pH of the solution, rather that the hydrogen ions dissociated from the acid contributes to the pH. Therefore, finding the pH of the concentration of HOCl and OCl- should not be in the example, nor should the example ask for the pH of all equilibrium concentrations, as that in itself is confusing.

4. Plagiarism Checks:

1. http://www.articlechecker.com/ : No plagiarism
2. http://www.dustball.com/cs/plagiarism.checker/ :No plagiarism
3. http://www.plagiarismchecker.com/url: No plagiarism