1.1 What is Chemistry?

21.2. The pH Concept http://www.ck12.org

Lesson Review Questions

1. Describe the characteristics of water which make it an amphoteric substance.


2. How do the concentrations of H 3 O+and OH−compare in pure water?


3. How do the concentrations of H 3 O+and OH−compare in an acid? In a base?


4. As the concentration of H 3 O+increases, does pH increase or decrease? Explain.


5. As the concentration of OH−increases, does pH increase or decrease? Explain.


6. What structural feature do Brønsted-Lowry bases and Lewis bases have in common?


7. How can acid-base indicators be used to approximate the pH of a solution?


8. How does litmus paper behave in an acidic solution versus in a basic solution?


9. Calculate the pH of the following solutions. Assume complete dissociation of each strong acid ([Acid] =
   [H+]):
   a. 4.5 x 10−^3 M HBr
   b. 1.34 x 10−^4 M HCl
   c. 7.98 x 10−^2 M HNO 3


10. Calculate the hydrogen ion concentrations in each of the following solutions:
    a. pH = 1.05
    b. pH = 5.65
    c. pH = 2.42


11. If the approximate pH of a solution is known, the indicators that will give you the most information are
    those for which the color change occurs near that pH value. Which indicator would you choose to check the
    approximate pH of the following solutions?
    a. pH ~ 4.1
    b. pH ~ 7.0
    c. pH ~ 2.4

Further Reading/Supplementary Links

• The pH scale: http://www.elmhurst.edu/~chm/vchembook/184ph.html


• How to calculate pH: http://www.csun.edu/~jeloranta/CHEM102/discussion7.pdf


• pH calculator: http://www.webqc.org/phsolver.php

Points to Consider

• How do we classify an acid as strong or weak?


• For a given concentration of acid, would you expect the pH to be lower for a strong acid or a weak acid?


• How can the relative strengths of various acids be quantified?