Posted by Maddie on .
The pH of an 0.0870 M solution of weak acid A is 2.20. The pH of an 0.0830 M solution of weak acid B is 4.07. The pH of an 0.0890 M solution of weak acid C is 5.13. Identify the three acids from among those listed below (the Ka values are listed in Appendix E of your textbook).
J None of the above
I'm not exactly sure what to do with the molarities... Any help please?
We will call weak acid A as HA.
pH = 2.20; therefore, H^+ = 6.31E-3
...........HA ==-> H^+ + A^-
You know x = 6.31E-3; therefore,
Ka = (H^+)(A^-)/(HA)
Ka = (6.31E-3)(6.31E-3)/(0.08069) = ?
Now look up the Ka values in Appendix E of your text and find the acid with the value you have above. That will identify the acid. Textbooks differ in what they print for the Ka/Kb values for weak acids and weak bases but I suspect acid A is HNO2.