Activity
Materials, for teacher:
Two beakers, any size
Triple-beam or any kind of balance
Glass stirrer
NaOH pellets
Two 1-L volumetric flasks
HCl, 15 M (molarity is commonly found on liquid reagent bottles.
HCl is usually 15M when purchased through chemical supply
companies. Some local companies may be able to prepare solutions
of a specific molarity for a fee)
Funnel
Droppers
Wash bottle
Teacher prep:
Solution preparation: CAUTION: Wear goggles, apron and rubber gloves when preparing
these solutions. HCl solution must be prepared under a hood.
NaOH
Weigh 40.0g of NaOH in a beaker, add enough distilled water
to dissolve it; do not add more than 200 or 300 ml. Transfer
to 1-L volumetric flask using a funnel and wash bottle.
Bring water level up to the 1-liter mark on the neck of
the flask using a dropper. Label flasks clearly with NaOH,
1M, include date.
HCl
Measure 15ml of 15M HCl using a pipette and transfer into
1-L volumetric flask. Bring water level up to the 1-liter
mark on the neck of the flask using a dropper. Label flask
clearly with HCl 1M, include date.
Class Demo:
1. Ask each student to generate a list of 15-20 words/ideas
they relate to chemical reactions. Organize these into a
concept or mind map.
2. In a 500mL-graduated cylinder, pour about 200mL of 1M
NaOH. Add three or four drops of phenolphthalein. Gradually
add 1M HCl, until the pink color disappears. The color
change of phenolphthalein from pink to clear indicates
an acidic solution. Use 1M NaOH to bring the color back
to pink and then add more 1M HCl to make a clear solution
again. Do this a few times. Write out the formula for HCl
and NaOH, on the board.
3. Ask students to pair up and come up with an explanation
for what they saw. Have them speculate about the reactants,
concentration and what it takes for the color to change.
4. Add three or four drops of methyl red indicator to the
mixture used in steps 1 and 2 above, and gradually add
1M NaOH until the color of the solution changes from red
to yellow. The color change to yellow indicates that the
solution now has a basic pH.
5. Repeat steps 1-3 a couple of times so students can see
how the reaction goes back and forth, noting the color
change. Have students make predictions about the color
change (Will it turn pink, red, etc.?) as the demonstration
progresses. Identify HCl and NaOH as an acid and a base.
Class discussion
6. Start asking students: “What happens between HCl and NaOH?”, “Why
do acids and bases matter to us?”, “What are some acids and bases
used at home?”, “How do we discard them?”. Present facts
about production of acids and bases by local businesses using provided teacher
background. Ask students if they live, or know anyone, who lives near one of
these businesses.
7. Have students add more terms on their concept maps this time using the demo
and including class discussion.
Closure
Students will exchange their concept maps with a classmate.
They will write down three main ideas represented on
their classmate’s concept map on a separate piece
of paper. Teacher will ask students to volunteer some
of the ideas.
Homework
Find three
examples of acids and three examples of bases commonly used
at home. Determine how each is discarded. Answer the question: “What
actually happens to them?”
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Embedded
Assessment
The
lesson will be assessed using the concept map. Collect and save
concept maps for future reference.
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