Weak Acids and Bases
What are Weak Acids and Bases?
Many common substances that we come in contact with are weak acids or bases such as vinegar Aspirin, and vitamin C. Weak acids and bases dissolve readily in water, however they do not ionize completely and instead form solutions containing unreacted molecules in dynamic equilibrium with the ions formed by the reaction of some molecules with water.
Many common substances that we come in contact with are weak acids or bases such as vinegar Aspirin, and vitamin C. Weak acids and bases dissolve readily in water, however they do not ionize completely and instead form solutions containing unreacted molecules in dynamic equilibrium with the ions formed by the reaction of some molecules with water.
LESSON OVERVIEW (SPECIFIC EXPECTATIONS E1.2, E2.1, E2.4, E3.4, E3.5, E3.6, E3.7)
Lesson Hook:
To highlight the similarities and differences of strong acids and bases versus weak acids and bases, a good opening activity would be to have students measure the pH of a few common household solutions of weak acids and bases, calculate the resulting H+ (OH-) concentration and then compare to that of a strong acid or base. A common misconception students have is that a weak acid or base will have a pH close to neutral. The above mentioned activity should negate this misconception and initiate some discussion as to the properties of weak acids and bases.
To highlight the similarities and differences of strong acids and bases versus weak acids and bases, a good opening activity would be to have students measure the pH of a few common household solutions of weak acids and bases, calculate the resulting H+ (OH-) concentration and then compare to that of a strong acid or base. A common misconception students have is that a weak acid or base will have a pH close to neutral. The above mentioned activity should negate this misconception and initiate some discussion as to the properties of weak acids and bases.
Action:
Following the opening activity, discuss the properties of weak acids and bases, the relationship between Ka, Kb, and Kw and the concept of percent ionization before having students extend their knowledge through the use of a computer simulation activity. This is a JAVA run computer simulation that allows students to investigate acids and bases. They are able to view strong and weak acids and bases on a molecular level as well as being able to determine the pH using a pH meter, pH paper and view conductivity. They can create a custom solution as well by setting the initial concentration and strength of an acid or base. Click below to download this simulation courtesy of the University of Colorado-PhET. Ideally, a worksheet or instruction document would accompany the simulation.
Following the opening activity, discuss the properties of weak acids and bases, the relationship between Ka, Kb, and Kw and the concept of percent ionization before having students extend their knowledge through the use of a computer simulation activity. This is a JAVA run computer simulation that allows students to investigate acids and bases. They are able to view strong and weak acids and bases on a molecular level as well as being able to determine the pH using a pH meter, pH paper and view conductivity. They can create a custom solution as well by setting the initial concentration and strength of an acid or base. Click below to download this simulation courtesy of the University of Colorado-PhET. Ideally, a worksheet or instruction document would accompany the simulation.
Acid-Base Simulation | |
File Size: | 1349 kb |
File Type: | jar |
Misconceptions Addressed:
1. Students commonly believe that when a `proton donor' acid reacts, the nucleus of an atom loses a proton.
2. Students commonly believe that a weak acid is a diluted acid or that strength and concentration mean the same thing.
Debrief:
Have students preform a 3-2-1 using the following headings:
List 3 Differences between strong bases and weak bases
List 2 Similarities between strong acids and weak acids
List 1 Question you still have
to hand in at the end of class as an assessment for learning before continuing on to acid-base properties of salt solutions.
FOPP: Commitment to students and student learning, professional knowledge, professional practice and ongoing professional learning
1. Students commonly believe that when a `proton donor' acid reacts, the nucleus of an atom loses a proton.
2. Students commonly believe that a weak acid is a diluted acid or that strength and concentration mean the same thing.
Debrief:
Have students preform a 3-2-1 using the following headings:
List 3 Differences between strong bases and weak bases
List 2 Similarities between strong acids and weak acids
List 1 Question you still have
to hand in at the end of class as an assessment for learning before continuing on to acid-base properties of salt solutions.
FOPP: Commitment to students and student learning, professional knowledge, professional practice and ongoing professional learning
The concept of Weak Acids and Bases can be reinforced in a variety of ways to appeal to all forms of multiple intellegences. Click below for a few resources that can be used in conjunction with a lesson to further demonstrate the concept of Weak Acids and Bases.