Acid And Alkaline.docx

I.

Learning Objectives: At the end of the lesson the students should be able to: a. Differentiate an acid from an alkali. b. Classify the substances present in the materials as acid or alkali using litmus paper. c. Recognize the characteristic properties of acid and alkali.

II.

Subject Matter: A. Specific Topic: Acid and Alkaline B. Reference/s: Evelyn C. Padpad et.al. The New Science Links pages 212216, Espana, Rebecca C.Chemistry:Updated Edition pages 268-271 C. Materials: vinegar, toothpaste, lemon, baking powder, ampalaya, tomato aspirin, distilled water, soap, blue and red litmus paper, transparent plastic cups, red and blue litmus paper, forceps, tap water, soft drink

III.

Procedures: A. ENGAGE Bring different materials in class. Let the students predict the taste of the following items (vinegar, toothpaste, lemon, baking powder, ampalaya, aspirin, distilled water, soap, tomato, etc.) Inform the students that each substance has certain properties and can be identified as acidic, alkaline and neutral.

B. EXPLORE Let the students carry out an experiment to identify acidic, alkaline or neutral substances. Activity: Comparing Acid and Alkali Materials: 10 transparent plastic cups 5 pcs. forceps 10 pcs. Red and blue litmus paper 1 bar of Soap (white) 1 pack Baking powder 3 pcs. Calamansi/lemon 1 bottle Vinegar 5 pcs. Aspirin 1 bottle Soft drink (colorless) 1 tube Toothpaste (colorless) 1 bottle Distilled water 500 mL Tap water(water from the faucet)

Procedure: 1. Label the plastic cups with the name of materials or substances. 2. Place the different materials on the different containers. (Note: Powder substances should be dissolved in distilled water.) 3. Place some water in one glass. This water will be used to rinse the forceps every time you use a strip of litmus paper. 4. Taste or feel the different substances. (If you know the taste of the different substances there is no need to taste it.) Record your observation in the observation table. 5. Prepare 9 strips of red litmus paper. Dip each strip of red litmus paper in the different substances. Observe the changes in color. 6. Prepare 9 strips of blue litmus paper. Dip each strip of red litmus paper in the different substances. Observe its reaction. Record all observations in the observation table. Then dispose of the pieces of litmus paper in the waste bin. 7. Classify the substances present in the materials as acid or alkali. Table 1: Observation Data on Acids and Alkalis

Substances 1. 2. 3. 4. 5. 6. 7. 8. 9.

Taste/Feel

The change in colour of litmus paper Blue litmus Red litmus paper paper

Types of Compounds (acid or alkali)

Soft drink vinegar toothpaste soap aspirin calamansi tapwater distilled water baking powder

C. EXPLAIN The teacher will discuss the activity performed by the students using the following guide questions: 1. What materials contain acid? 2. What materials contain alkali? 3. What is the reaction of the strip of blue litmus paper when dipped into an acid containing substance? 4. How about the reaction of the strip of red litmus paper when dipped into a substance or material containing a base? 5. What did you use as an acid –alkali indicator?

Discussion Proper: How can you distinguish an acid from an alkali? Acids are compounds that contain hydrogen.When dissolvedin water, an acid releases hydrogen ions. Hydrogen ions are positively charged and have the formula (H+). Alkalis are described as the “opposite “ of acids .Alkalis or bases are substances that produce hydroxide ions when they dissolve in water. Hydroxide ions are negatively charged and have the formula (OH-). The presence of the H+ ions gives acids their characteristic properties such as sour in taste and corrosive to metals. Alkalis are compounds that can be identified by their common properties such as bitter in taste and feel soapy and slippery to touch. How can you detect the presence of acids and alkalis in some substances in a solution? The presence of acids and alkalis can be detected with the use of a complex organic substance known as indicator which shows specific color change when it comes in contact with a n acid or alkali. Common Acid and Alkali Indicators Indicator Color in Acid Color in Alkali Litmus paper red blue Universal pH paper red violet Methyl orange red yellow Phenolphthalein colorless pink If neither red nor the blue litmus paper changes colour, the substance is neutral. Note: Encourage the students to use the terms correctly. ‘Acid’ and ‘alkali’ are nouns; the words ‘acidic’ and ‘alkaline’ are adjectives. ‘A solution of vinegar is acidic. Vinegar is an acid.’

D. ELABORATE

Graphic Organizer: Make a comparison of the two words using a Venn Diagram. Using the information below, cite the similarities and differences between an acid and an alkali.

ACID

BOTH

ALKALI

Bitter Taste

Corrosive to Metals

Feel Slippery and Soapy

Fruits and Juices

Release Hydrogen Ions

Conducts Electricity

Release Hydroxide ions

Sour Taste

Change the Colour of Litmus Paper

Cleaning Products

E. EVALUATION I. 1. 2. 3. 4. 5.

Classify each of the following substances as acidic or alkaline.

Soap solution Apple Juice Cough Syrup Liquid Sosa Toothpaste II. Distinguish between : Acid and Alkali

F. EXTEND Homework:

Read and answer the following questions: Acid Rain In a polluted environment, rain can be slightly acidic or very acidic. Water dissolves carbon dioxide gas from the air forming carbonic acid (H2CO3).Gaseous air pollutants can acidify the rain . Normal rain has a pH level of 5.6 while acid rain has a pH level of less than 5.6. The main pollutants responsible for acid rain are sulphur and nitrogen oxides. These pollutants come from automobiles and industrial plants that burn coal and oil. In the atmosphere, sulphur oxide reacts with water vapour, forming sulphuric acid (H2SO4), and nitrogen oxide reacts with water vapour, forming nitric acid (HNO 3). 1. What are the compounds that contribute to the formation of acid rain? 2. What are the different acids present in the acid rain? 3. How is acid rain formed?