Due: Monday, December 6, 2010
Rachelle Lee
Introduction
a) Objectives for the overall “unit” (no more than 3!)
Students will know how to figure out if a solution is acidic, basic or neutral.
Students will be able to neutralize an acidic or basic solution.
Students will know why acids and bases are valuable in our everyday lives.
b) Why you think this is a suitable topic
Every chemical, whether at home or in the lab, is either an acid or a base. Knowing what to expect from acid-base
reactions helps us understand if a reaction is an acid-base reaction, as well as what can happen in acid-base
reactions.
c) Curriculum fit/curriculum objectives
Science 10 – CR 5 – Investigate chemical reactions involving acids and bases
-Classify substances as acids, bases, or salts, based on observable characteristics, name, and chemical formula.
-Describe the process of neutralization and identify practical examples.
- Perform activities to investigate the characteristics of acids and bases.
d) How you will judge the overall success of the “unit”
The success of this unit will be determined by the final extend activity and the evaluation of that activity. That
activity pulls together everything they have done in this unit, as well as helps them think critically about how to
solve a problem scientifically.
e) Best estimate of an ideal time
Engage – 15-20 minutes
Explore 1 – 1 hour
Explore 2 – 1 hour
Explain – 1 hour
Extend – 1.5 hours
Engagement Activity – Alka-Seltzer Rainbow
a) Materials and safety
Alka-Seltzer, 1 tablet
Vinegar, CH3CO2H, 10 mL
Sodium hydroxide, NaOH, 0.1 M,
100 mL Beaker, 600-mL
Universal indicator, 10 mL
Graduated cylinders; 500-mL, 100-mL and 10-mL
Water, distilled, 350 mL
Stirring rod
Sodium hydroxide is a corrosive liquid, skin burns are possible and it is dangerous to the eyes. Universal indicator is
an alcohol-based solution and thus a flammable liquid. Wear chemical splash goggles, chemical-resistant gloves, and
a chemical resistant apron. Please consult current Material Safety Data Sheets for additional safety information.
b) Description of activity
1. Drop an Alka-Seltzer tablet into the 500-mL graduated cylinder containing the water, NaOH and universal indicator.
Color changes should begin to occur as soon as the first carbon dioxide bubbles are formed.
2. When the tablet rises to the top, add about 10 mL of vinegar to the solution. The solution should now be red on the
top.
c) Background info (science behind it)
The Alka-Seltzer tablets contain sodium bicarbonate and citric acid. As the Alka-Seltzer tablet dissolves in water, the
citric acid reacts with the sodium bicarbonate to produce carbonic acid (Equation 1) and carbon dioxide (Equation 2).
The carbonic acid then reacts with the basic sodium hydroxide to change the pH of the solution (Equations 3 and 4).
As the base is consumed, the solution will slowly become more acidic, resulting in the color changes.
HCO3- + H+ H2CO3 Equation 1
H2CO3-H2O + CO2 Equation 2
H2CO3 + OH- HCO3- + H2O Equation 3
HCO3- + OH- CO32- + H2O Equation 4
The Alka-Seltzer tablet initially sinks to the bottom of the cylinder. As the carbon dioxide bubbles adhere to the tablet,
the tablet begins to rise and eventually floats. The buoyancy of the tablet and the final addition of vinegar (a weak acid)
show a pH gradient. Universal indicator makes the pH gradient visible and produces the characteristic rainbow of
colors.
d) Questions to ask to stimulate thinking and assess prior knowledge (and expected answers)
-What do you know about vinegar? About alka-seltzer? (weak acid used in baking)(used to calm heartburn/neutralize
excessive stomach acid)
-What happens when vinegar reacts with baking soda? (foams and bubbles, acid-base reaction, carbon dioxide is
formed)
e) What you hope the students take away
I hope the students take away questions and possible theories for what they observed, as well as possible ways to test
their inferences.
f) Source - http://www.csun.edu/chemteach/activities/CF10456.pdf
Exploration Activity (1) – Cabbage Juice Indicator
a) Materials and safety
hot plate
1 head red cabbage
Food processor
1000 mL beaker
500 mL beaker
4-5 250 mL beakers
Sieve
Substances to test
Distilled water
Rubbing alcohol
** recommended materials: baking soda, bathroom cleaner (e.g. Formula 409™), washing soda, vinegar, lemon juice,
milk, cream of tartar, orange juice, milk of magnesia, lime, soft drinks, or ammonia
Due to the dangerous nature of the chemicals that are used, students must wear safety goggles and handle all
substances with proper care and attention to safety.
b) Description of activity
1. Chop red cabbage up finely. Boil a pint of water in a saucepan.
2. Add the red cabbage carefully to the boiling water and take the saucepan off the heat. Let it stand for 30 minutes or
until it is completely cool.
3. Strain the liquid into a jar and throw away the used cabbage. The liquid should be a dark reddish-purple color. Add
rubbing alcohol, or refrigerate, to reduce the spoilage of the indicator. Use a 1:5 ratio of alcohol to water.
4. The color will change as you add acids or alkalis. To test a substance, pour a small amount of your substance into
a small jar. Then add a drop or two of the cabbage juice indicator. A change in color indicates its acidity or basicity.
5. Disposal: All solutions can be poured down the sink. Solid bits of cabbage should be put into a solid waste
container and emptied at the end of the school day, owing to their odiferous nature.
c) Background info
The cabbage juice is an indicator. It changes from red (highly acidic) to yellow (highly basic) and is purple for neutral
substances. The lemons, vinegar, cream of tartar, orange juice and sour milk will be acidic. The baking soda,
bathroom cleaners, ammonia, washing soda, milk of magnesia and lime will be basic. Pure distilled water is the only
substance listed that will be neutral. Tap water can be slightly acidic because of the dissolved carbon dioxide.
d) Questions to ask that stimulate thinking and/or check for understanding of the activity (and expected answers)
What does the color change in the cabbage juice tell us? (That the substance is acidic/basic)
Which substances were acidic? (lemons, vinegar, cream of tartar, orange juice, tap water and sour milk)
How do you know these substances are acidic? (the cabbage juice turned a red color)
Which substances were basic? (baking soda, bathroom cleaners, ammonia, washing soda, milk of magnesia and lime)
How do you know these substances are basic? (the cabbage juice turned a yellow or green color)
Were any substances neutral? (pure distilled water)
How do you know these substances are neutral? (no color change observed)
Were the household cleaners acidic or basic? (mostly basic) Why do you think this is? (Bases convert oils to soap,
making them good cleaners)
Why is tap water slightly acidic? (Because of the dissolved carbon dioxide.)
e) What you hope the students take away
Students will understand how they can easily test to see if a solution is acidic, basic or neutral. The students will also
take away an understanding of what types of household products are acids and bases, and why they are that way.
f) Source - http://www.science-house.org/learn/CountertopChem/exp22.html
Exploration Activity (2) – Neutralization Activity
a) Materials and safety
burettes
burette stand
graduated cylinder
Erlenmeyer flask
beakers
dropper pipette
pipette
0.1M standard solution HCl
Concentrated NaOH solution
Phenolphthalein
Distilled water
Since students will be working with a highly concentrated NaOH solution, safety goggles must be worn at all times.
Also, students must hand the chemicals with due care and attention.
b) Description of activity
1. Pour about 10ml of acid into one burette and rinse the inside surface of the burette thoroughly. Allow the acid to run
out the burette tip. Fill the burette with the acid. Be sure there are no bubbles in the tip.
2. Place a 125ml Erlenmeyer flask under the acid burette as in the figure. Allow exactly a 10.0ml of acid to flow into
the flask.
3. At exactly 10.0ml of distilled water to the flask. Then add three drops of phenolphthalein. Swirl the flask to mix all
the ingredients.
4. Swirl the flask gently; begin the titration by adding NaOH to the flask drop by drop. Continue until the solution
becomes pink.
5. Note and record the exact final volume reading on the scale of the base burette.
6. If time is enough, repeat the steps 4 to 6.
c) Background info
It is sometimes necessary to determine experimentally the concentration of an acid solution or a base solution. In an
acid-base titration, a solution with a known concentration, called standard solution, is used to neutralize a solution with
an unknown concentration to which a few drops of an appropriate acid-base indicator is added. If the solution of
unknown concentration is acidic, a standard base solution is added to the acid solution drop by drop until it is
neutralized; and vice versa.
While doing an acid-base titration, you must be able to recognize when to stop adding the standard solution. A sudden
change in color indicates that neutralization has occurred. At this point, the number of hydronium ions from the acid is
equal to the number of hydroxide ions from the base. The point at which this happens is called the end point of the
titration. When this point is reached, the volume of the standard solution used must be carefully determined. Then,
measured volumes of the two solutions and the known concentration of the standard solution can be used to calculate
the concentration of the other solution.
d) Questions to ask that stimulate thinking and/or check for understanding of the activity (and expected answers)
What is created when a base is neutralized with an acid or vice-versa? (It creates a salt solution)
How did you know when the HCl was neutralized? (It was longer pink)
If we know the concentration of the acid, and the amount of acid and the amount of base used to neutralize them, can
we find the concentration of the base? (Yes, through proportional reasoning. [base]/[acid]=amount of base/amount of
acid)
Why is it important to understand how to neutralize a base or acid? (It is important to understand how acids and bases
react with each other, as well as how to neutralize a danger solution to make it safer.)
e) What you hope the students take away
Students will take away an understanding of how to neutralize a dangerous acid or base, thus making it a salt solution.
Students will also understand why it is important to know how to neutralize an acid or a base.
f) Source - http://www.siraze.net/chemistry/sezennur/subjects/experiment/028.pdf
Explain Activity
a) Questions (and expected answers)
What are some similarities between the acids we have looked at? (Corrosive/burns your skin, sour tase, has pH<7,
reacts with bases to form salt and water, most create H+ ions when dissociated in water)
Where can we find acids in everyday life? (Some household cleaners, vinegar, some citrus fruits, carbon dioxide, soda
pop)
What are some similarities between the bases we have looked at? (Corrosive/burns your skin, soapy feel, has ph>7,
reacts with acids to form salt and water, most create OH- ions when dissociated in water)
Where can we find bases? (Many household cleaners, baking soda, antacids, washing detergent)
How can you find out if a solution is acidic or basic? (Using an indicator)
What does the pH scale measure? (Acidity/basicity)
What career fields are pH measures important in? (medicine, biology, chemistry, food science, environmental science,
oceanography, civil engineering, etc.)
b) Background definitions and principles you want to be sure that you and students arrive at
Bronsted-Lowry Acid – any substance that can donate a hydrogen ion
Bronsted-Lowry Base - any substance that can accept a hydrogen ion
The BL acid donates a H+ ion, while the BL base donates a OH- ion to create water. The leftover atoms combine to
create a salt in an acid/base reaction.
Indicator – A chemical that, when used, indicates whether a given solution is acidic or basic.
Extend Activity
a) Materials and safety
burettes
burette stand
graduated cylinder
Erlenmeyer flask
beakers
dropper pipette
pipette
phenolphthalein
highly conc. acidic solution
highly conc. basic solution
1.0 M standard HCl solution
1.0 M standard NaOH solution
Since the students will be dealing with highly concentrated solutions of HCl and NaOH, safety goggles must be worn at
all times. Also, appropriate lab behaviour must be used at all times.
b) Description of activity
1. Students will design a method to test whether their given solution is acidic or basic, and then must neutralize it
using the titration method learned in the second explore activity.
2. Each student will be given either a concentrated HCl or NaOH solution. (They will not know what they have, nor will
they know that they have one of only two different solutions)
3. Students will then use the phenolphthalein to see if their solution is acidic or basic. They must then titrate until their
solution is neutralized.
c) Background info
It is sometimes necessary to determine experimentally the concentration of an acid solution or a base solution. In an
acid-base titration, a solution with a known concentration, called standard solution, is used to neutralize a solution with
an unknown concentration to which a few drops of an appropriate acid-base indicator is added. If the solution of
unknown concentration is acidic, a standard base solution is added to the acid solution drop by drop until it is
neutralized; and vice versa.
While doing an acid-base titration, you must be able to recognize when to stop adding the standard solution. A sudden
change in color indicates that neutralization has occurred. At this point, the number of hydronium ions from the acid is
equal to the number of hydroxide ions from the base. The point at which this happens is called the end point of the
titration. When this point is reached, the volume of the standard solution used must be carefully determined. Then,
measured volumes of the two solutions and the known concentration of the standard solution can be used to calculate
the concentration of the other solution.
d) Questions to ask to stimulate thinking and assess prior knowledge (and expected answers)
Why is important to understand if an unknown solution is acidic or basic? (So we can better predict what will happen if
we react it with other chemical)
e) What you hope the students take away
I hope the students take away an understanding of how to design their own experiment, as well as a furthered
knowledge of how to figure out if a chemical is an acid or a base and how to neutralize an unknown acid or base.)
f) Source – Derived from the experiments listed above
Evaluation (1) – Demo Memo for the Engage Activity
a) Aim(s) for the assessment
-Students will record observations
-Students will record their inferences and why they think that their inference is a valid response.
b) Expected responses
-Students will have recorded their observations (alka seltzer bubbled, color change, more color change when vinegar
added, tablet floats after awhile)
-Students will record their inferences (acid/base reaction, vinegar makes solution go one color while NaOH makes it go
another color, alka-seltzer floats because the carbon dioxide bubbles make it rise)
c) Rubric for assessment
Observations
Explanation
2
-All observations
recorded thoroughly
-1 or more explanations
suggested
-Thorough reasoning for
explanations stated
1
-Some observations
recorded
-1 explanation
suggested
-Some reasoning stated,
although it is not well
thought out
0
-No observations
recorded
-No explanations given
Evaluation (2) – Poster for the Extend Activity
a) Aim(s) for the assessment
-Students will record their experimentation method and results.
-Students will be able to test a solution to see if it acidic or basic
-Students will be able to successfully neutralize an acidic/basic solution
b) Expected responses
-Students will have determined if their solution is acidic or basic, as well as successfully neutralized their solution.
-Students will have created a poster as a creative way to record their process as well as their observations, results and
inferences.
c) Rubric for assessment
4 – Above and Beyond
3 – Well Done
Work Ethic
Used time well during the
class period. Consistently
focused on getting the
project done. Almost never
distracted others
Used time well during each
class period. Usually focused
on getting the project done
and almost never distracted
others.
Title
Title can be seen from 6 ft
away. Stands out. Is quite
creative.
The poster contains an
introduction, the entire
experimentation method, as
well as observations, results
and inferences as to what
you think the solution is.
The poster is interesting,
creative and very neat.
Title can be easily read from
6 ft away and stands out.
Requirements
Neatness and
Creativity
The poster contains an
introduction, the entire
experimentation method, as
well as observations and
results.
The poster is very neatly
done.
2 – OK, but Needs Some
Improvement
Used some of the time well
during the class period.
Some focus on getting the
project done, but
occasionally distracted
others.
Title is too small to be seen
from 6 ft away OR does not
stand out.
The poster contains an
introduction, most of the
experimentation process,
observations and results.
1 – Oops!
The poster is fairly neat,
although parts of it could be
neater.
Most of the poster could be
neater.
Did not use class time to
focus on the project OR
often distracted others.
No title.
The poster is completely
missing an introduction OR
the experimentation process
OR observations OR results.
Comments on this Assignment
I found this assignment really helpful in learning how to plan a unit that will be interesting to students and still help them
learn what the Ministry of Learning has said that they need to know. I really enjoyed searching for activities that will be
fun, hands-on, and educational.
The part I found most difficult was the extend activity. It took me a while to figure out how to pull everything together in a
fun and interactive way. Also, I have trouble with determining how long an activity will take, so the timing is something I
need to work on. However, I don’t think that that’s something I can learn by planning. That is something I need to learn by
being out in the field and teaching different classes. I also realize that timing will be different for every class, so to say that
this Learning Cycle will take four and a half hours is just a rough estimate.