Introduction
Making chemistry concepts “stick” can sometimes require a memorable chemical demonstration or a cross-curricular concept, or even both at the same time! In this activity, students revisit acid-base reactions and net-ionic equations with a little help from the Sharks and the Jets from West Side Story.
The demonstration highlights two concepts: testing for electrolytes and acid-base indicator solutions. Students are able to determine qualitatively the concentration of electrolytes in solution by observing the brightness of the conductivity bulb. Students are also able to determine the equivalence point between the reaction of an acid and a base by observing color changes of the indicator solution.
Below is a lesson plan from warm-up to ticket-out1 that
I have used in my junior-year (11th grade) college-preparatory chemistry class.
Warm-Up
Students should be able to predict the products (in both words and formulas) for the double replacement reaction of the following: barium hydroxide dissolved in water reacts with an aqueous solution of sulfuric acid. Students are asked to use their solubility rules and include states!
The lab set up is drawn in student lab notebooks.2
Targets
Students will be able to write a net-ionic equation of an acid-base reaction. They will observe evidence of the chemical reaction and write a net-ionic equation for the reaction between an acid and a base.
Demonstration
Students will be observing an acid-base titration. With the demonstration, students will observe the conductivity of the solution. As shown in the setup, 5 g of barium hydroxide is added to a beaker of distilled water. Phenolphthalein is added.
A burette will slowly deliver 0.5 M sulfuric acid. As the titrant is added, students will observe and record the intensity of the light, color of solution and the formation of a precipitate (if one forms).
Observations
Students should observe the light on the conductivity tester decrease in brightness as the titrant is added and the solution approaches equilibrium. Students will also observe the formation of a white precipitate — it should look like milk. At equilibrium, students should be able to observe a color change — pinkish-white to white — and the conductivity light goes off. Then as the acid continues to be added, the light will turn on and begin to increase in intensity.
Student questions
- What observation(s) indicate a chemical change has occurred?
- For the reaction, use chemical formulas and ions with the given diagram to help describe the following scenarios: the light goes on, the light goes off and the light goes on again.
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Use the model of the ions above to answer the questions below:
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Why does the light initially go on when the barium hydroxide is dissolved in the beaker?
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Why does the light dim and eventually go out as the sulfuric acid from the burette is added to the beaker?
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Why does the light go back on as the burette is left open indefinitely?
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- Why does the phenolphthalein indicator solution turn pink at the outset of the experiment?
- Why does the solution change color as the sulfuric acid is added?
- What do you notice about the timing of the bulb’s brightness and the solution’s color change?
- Write the ionic equation for the chemical reaction between barium hydroxide and sulfuric acid.
- Write the net-ionic equation for the chemical reaction.
West Side Story analogy
Ticket Out (your ticket out of class): Watch the YouTube clip of West Side Story and write the net-ionic equation for "West Side Story".
Teacher’s notes
In this scene of West Side Story, the Jets and the Sharks, two opposing gangs in New York City, show up at the same dance hall. Once the Mambo dance begins, all participants are dancing on their own on the dance floor (soluble ions in solution). At the 3:00 minute mark on the video, Tony (of the Jets) and Maria (of the Sharks) see each other from across the room (beaker) and are the only dancers to pair off (insoluble compound). The net-ionic equation is shown below:
Tony (aq) + Maria (aq) --> Tony-Maria (s)
A little suspension of belief is required here!
Reference and notes
- Ticket-out is exactly what it sounds like. If students finish the task, they can leave class.
- “Acid/Base Light Demonstration”, Doug Zimmer, Wheaton Warrenville South High School, Wheaton, IL. This demonstration was presented at a ChemWest Teacher meeting in May 2012 at Doug’s school. Doug saw this demonstration at a sharing session years earlier but was unsure of its origins.
Handout:
https://docs.google.com/file/d/0B_mH8xKqPXAmQy00T1pabGxILW8/edit (need to use gmail account to access this document)
Video: (3 minute) of presentation (recommended) https://vimeo.com/42904123
