Transcript acids and bases - sukgr11chemistry

Acids and Bases
Swati Kulkarni & Rajmeet Virdi
Introduction of the topic
Acids and bases are chemical compounds that
have distinctive properties in water solution.
The sour taste of a lemon, lime, or grapefruit,
for example, is caused by citric acid. The
slippery feel of ammonia, a common base, is
characteristic of all bases. Bases tend to taste
bitter. Acids and bases show different colors
with different substances. These substances
are called indicators.
Specific
Expectations
E3.5 Explain the Arrhenius theory of acids and
bases
E3.6 Explain the difference between strong and
weak acids, and between strong and weak
bases, in terms of degree of ionization
E2.7 Determine the concentration of an acid or a
base in a solution (e.g., the concentration of
acetic acid in vinegar), using the acid–base
titration technique.
HOOK…Concept Attainment
Tomato
Milk
Vinegar
Baking Soda
Vitamin C
Toothpaste
Lemons
NaOH
Wine
Limewater
HCl
Oven Cleaner
Testers:
•Underarm Odour
•Borax
•Eggs
•Sour milk
One more HOOK…Story of Ira Remsen
This demonstration has its roots in the writings of Ira Remsen, a 19th century professor of
chemistry at Johns Hopkins University. In his memoir, Remsen writes....
"While reading a textbook of chemistry I came upon the statement, nitric acid acts upon copper. I
was getting tired of reading such absurd stuff and I was determined to see what this meant. Copper was
a more or less familiar to me, for copper cents were then in use. I had seen a bottle marked nitric acid on
a table in the doctor's office where I was then doing time. I did not know its peculiarities, but the spirit of
adventure was upon me. Having nitric acid and copper, I had only to learn what the words acts upon
meant . The statement nitric acid acts upon copper would be something more than mere words. All was
still. In the interest of knowledge I was even willing to sacrifice one of the few copper cents then in my
possession. I put one of them on the table, opened the bottle marked nitric acid, poured some of the
liquid on the copper and prepared to make an observation.
But what was this wonderful thing which I beheld? The cent was already changed and it was no
small change either. A green-blue liquid foamed and fumed over the cent and over the table. The air in
the neighborhood of the performance became colored dark red. A great colored cloud arose. This was
disagreeable and suffocating. How should I stop this? I tried to get rid of the objectionable mess by
picking it up and throwing it out of the window. I learned another fact. Nitric acid not only acts upon
copper, but it acts upon fingers. The pain led to another unpremeditated experiment. I drew my fingers
across my trousers and another fact was discovered. Nitric acid acts upon trousers. Taking everything
into consideration, this was the most impressive experiment and relatively probably the most costly
experiment I have ever performed... It was a revelation to me. It resulted in a desire on my part to learn
more about that remarkable kind of action. Plainly, the only way to learn more about it was to see its
results, to experiment, to work in a laboratory."
http://lsd.k12.mi.us/~eastchem/demonstrations/iraremsen.html
What do the students need to
know….
 Theories of acids and bases
Strong and weak acids and bases
Acid-Base reactions
Lesson Sequence
1. Introduction to Acids and Bases
2. Arrhenius concept of acids and bases
3. Strong and weak acids and bases
4. pH of acids and bases
5. Neutralization reaction
6. Titration in the lab
Lab Investigation:
The pH Rainbow Column
Teaching tips:
 Before the lab make sure students know about universal indicator
that undergoes several color changes as it’s pH changes.
 Go over Safety Precautions: The solutions of sodium carbonate
and hydrochloric acid are both irritants. Avoid skin contact. If
some does spill on your skin, wash the affected area with plenty
of cool water. Report any spills to your teacher.
 A discussion should follow up this activity, helping students to use
the color changes of Universal Indicator to monitor the
neutralization of an acid with a base.
Student difficulties and misconceptions:

Students may think that a higher pH value means more acidic-it is
the opposite!
Arrhenius concept of acids
and bases
Acids are substances which dissolved in water
dissociate to give H+ ions and bases are
substances which dissociate in water to give
OH- ions.
Inquiry based activity – Strong
and weak acids and bases
The following link is to a video which can be
used to initiate the topic:
http://www.youtube.com/watch?feature=player_
detailpage&v=kcPjY9cQpWs
Activity is performed to show that strong acids
and bases dissociate completely in water
where as for the weak acids and bases
dissociation is incomplete.
pH of substances
The pH scale measures how acidic or basic a
substance is. pH can range from 0 to 14.
A pH less than 7 is acidic. A pH of 7 is neutral.
A pH greater than 7 is basic.
Acid and Base Titration- An Interesting
Video

http://www.youtube.com/watch?v=lCrMB8
341rU&feature=related
Acids and Bases: Titration Lab
Teaching Tips


Before starting the titration lab, perform a quick review and check how well
students are at determining the concentration of a diluted solution from a
standard solution before they perform any calculations
Review safety rules such as wearing safety goggles, lab apron, handling
chemicals and clean up procedures.
Student Misconceptions

Students may think the neutralization of a substance requires just an acid
and a base, however, it must be a strong acid and a strong base to
neutralize a substance.
Acids and Bases-Computer
Animation

http://www.chembio.uoguelph.ca/educmat/ch
m19104/chemtoons/chemtoons.htm
Student difficulties and
misconceptions


Students may think that a higher pH value means
more acidic-it’s the opposite!
Students may use concentrated and strong
interchangeably- this is wrong! Reinforce that
‘concentrated’ (having a high concentration of
particles in mol/L) is different from ‘strong’
(dissociates 100%) and ‘weak’ (dissociates much
less than 100%) is different from ‘dilute’(having a
low concentration of particles in mol/L).
Accommodation for special need students
and English Language Learners
Following accommodations will be made:
1)
providing additional time to complete tests or assignments
2)
permitting oral responses
3)
computer options and use of technology
4)
preferential sitting as outlined in their Individual Education Plans
(IEPs). Gifted students can be challenged to complete extensions
of topics covered in class to their everyday lives such as using
green alternatives for chemicals
5)
extensive use of visual clues such as - graphic organizers, preteaching vocabulary, pre-viewing text books, peer tutoring, using a
variety of learning resources such as bi-lingual dictionaries and
simplified simplified texts.
Assessment & Evaluation








Quiz on Acids and Bases (Knowledge/Understanding)
Pre Lab Revise Lab Safety Rules
Formal Lab Acid – Base Titration (Thinking/Inquiry)
Activity for strong and weak acids and bases (Inquiry/investigation)
Reflective Response on Demonstration (Communication)
Lab Report (Titration/Inquiry) (Communication)
Culminating Task Rubric for research project and oral
presentations (Communication, Application)
Unit Test (Knowledge/Understanding, Application, and
Communication) with emphasis on Application of the concepts
learned.
Practical Application and Societal
Implications









Neutralization has many practical applications. Reclamation (restoration) of land
once used for mining also involves neutralization reactions
Neutralization is also used to deal with environmental problems.
Acids and bases are used in the manufacture of fertilizers, synthetic fabrics,
pigments, petroleum, iron and steel, explosives, dyes, plastics, pesticides,
soaps and detergents, paper, film, and many other chemicals
They are also used for various other purposes, including cleaning surfaces,
refining oil and sugar, electroplating metals, and treating food products.
Sulfuric acid is the chemical most widely used in industry.
Nitric acid, another important industrial acid, is used in the manufacture of
fertilizers, plastics, photographic film, and dyes and explosives as dynamite and
TNT.
Hydrochloric acid is used to clean metals, brick and tile; it is used in the
manufacture of sugar and glue.
pH plays an important role in the chemistry of the body.
Softening of water using soda lime process by municipalities and wastewater
treatment.
Cross curricular links





Biology/Life Sciences - Students know enzymes are proteins that
catalyze biochemical reactions without altering the reaction
equilibrium and the activities of enzymes depend on the
temperature, ionic conditions, and the pH of the surrounding, pH of
the mouth, tooth decay, acidity in stomach, cure of bee and wasp
sting.
Mathematics - Calculation of pH of a given solution(extension)
Environment - pH of the soil, acid rains due to environmental
pollution
Music- A rap song on pH and another on properties of acids and
bases
Home Science- The salts in the kitchen and usage of the salts for
various household activities.
Internet sites which can be
referred for this topic
http://www.scienceclarified.com/A-Al/Acids-and-Bases.html
This web site is an excellent resource for practical applications of acids and bases.

http://www.sciencebyjones.com/acids_bases_salts.htm
This web site leads to different areas of interest such as properties, definitions, questions
and problems about acids and bases.

http://www.ehs.pvt.k12.ca.us/projects/9798/science6/Stephanie
This is a web page containing information about litmus and pH

http://www.chembio.uoguelph.ca/educmat/chm19104/chemtoons/chemtoons.htm
The variety of animations about acids and bases are self-explanatory

http://www.youtube.com/watch?v=PCM5IwJ8wcs
A very informative video on acids and bases

http://www.visionlearning.com/library/module_viewer.php?mid=58
This site is a step by step guide to teach acids and bases

http://library.thinkquest.org/10429/low/acidbase/acidbase.htm
This web site is an excellent source to learn about the theories of acids and bases.
