Lesson 1: Introduction using acidic and basic food and household items
Objectives: The students will be able to apply prior knowledge of the characteristics of food and household substances to the topic of acid-base chemistry.
The students will be able to the identify pH of substances.
The students will be able to describe acidic and basic properties.
The students will be able to identify acidic and basic substances.
Standards Addressed by Lesson: Standards
Concept: This lesson is an introduction to acid-base concepts. The students will observe the properties of acids and bases through activities. Theories and properties of acids and bases will be addressed.
Exploration Activity: 1 In groups of four, students will observe the reaction between baking soda (sodium hydrogen carbonate) and fruits and vegetables. Those with sour or tart tastes will react to produce carbon dioxide gas, observable as bubbles. Students will refer to prior knowledge and observations of the reaction to identify the fruits and vegetables with acidic properties.
Materials: lemon, orange, grapefruit, tomato, celery, banana, and apple sliced (1 slice of each per group); 1 box of baking soda (NaHCO3); paper towels; 6 beakers
Data Collection: Students should observe and record the type of reaction that occurs between each food item and the baking soda.
Concept Introduction: Which foods reacted with the baking soda? The lemon, orange, grapefruit, and tomato react. What is similar between them? They all have a tart or sour taste. What happened when the baking soda and the foods reacted? Bubbling occurs from the carbon dioxide gas that is produced. Introduce vocabulary, theories, and concepts. Refer to Teacher Notes and Student Notes.
Application Activity:1 In groups of four, students will use a pH indicator to observe the color changes that occur at various pH’s and classify common substances as acids or bases. The indicator (red cabbage juice) is purple. When the indicator is added a neutral substance will remain purple; acidic, red; basic, green. The cleaning items will test mostly basic. Hygienic substances will test mostly neutral. Identify, compare, and contrast the chemical components of the known acidic and basic substances. Household pH lab
Materials: red cabbage juice indicator (prepared prior to lab); 54 beakers (9 per group); 18 sheets of white paper (3 per group); 1 bottle of white vinegar (CH3COOH); 1 box of baking soda (NaHCO3); household ammonia (NH3); 6 droppers; laundry detergent; milk of magnesia; mouthwash; carbonated beverage; shampoo; dish soap
Indicator prep: Combine 3 cups of chopped red cabbage leaves and 3 cups of hot water. Stir and crush leaves until water is distinctly colored purple. Strain extract through a cloth into a clean container.
History: Acid and Base Theories:
1887- Swedish chemist Svante Arrhenius
1923- Danish chemist Johannes Brønsted and English chemist Thomas Lowry
1923-American chemist Gilbert Lewis
Websites:
Visionlearning, Acids and Bases: An Introduction http://www.visionlearning.com/library/module_viewer.php?c3=&mid=58&l
Chemical & Engineering News, “An Eye on Food”
http://pubs.acs.org/cen/coverstory/83/8327food.html
Oregon State University, Food Resource
http://food.oregonstate.edu/learn/ph.html
References:
1. Wilbraham, A.C., et.al. “Chapter 19.1: Acids, Bases, and Salts.” Chemistry. Prentice Hall: 2005. 586-593, 604.