Acids and Bases

1. Acids and Bases Swati Kulkarni & Rajmeet Virdi

2. Introduction to 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.

3. 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.

4. HOOK…Concept Attainment • Testers: • Underarm Odour • Borax • Eggs • Sour milk

5. 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

6. What do the students need to know….  Theories of acids and bases Strong and weak acids and bases Acid-Base reactions

7. 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

8. 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!

9. 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.

10. 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.

11. 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.

12. Acid and Base Titration- An Interesting Video • http://www.youtube.com/watch?v=lCrMB8341rU&feature=related

13. 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.

14. Acids and Bases-Computer Animation • http://www.chembio.uoguelph.ca/educmat/chm19104/chemtoons/chemtoons.htm

15. 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).

16. Accommodation for special need students and English Language Learners Following accommodations will be made: • providing additional time to complete tests or assignments • permitting oral responses • computer options and use of technology • 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 • extensive use of visual clues such as - graphic organizers, pre-teaching vocabulary, pre-viewing text books, peer tutoring, using a variety of learning resources such as bi-lingual dictionaries and simplified simplified texts.

17. 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 forresearch project and oral presentations (Communication, Application) • Unit Test (Knowledge/Understanding, Application, and Communication) with emphasis on Application of the concepts learned.

18. 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.

19. 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.

20. 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.