CR5 Investigate chemical reactions involving acids and bases

Suggested time: 3-5 hours

Learning Objectives

1. Perform activities to investigate the characteristics of acids and bases. (IL)
   
2. Work co-operatively with team members to develop and carry out a plan, and troubleshoot problems as they arise. (CD 2.3)
   
3. Evaluate and select appropriate instruments for collecting evidence and appropriate processes for problem solving, inquiring, and decision making. (CCT, TL)
   
4. Classify substances as acids, bases, or salts, based on observable characteristics, name, and chemical formula.
   
5. Name and write formulas for common acids and bases, using the periodic table, a list of ions, and rules for naming acids and bases.
   
6. Describe the process of neutralization and identify practical examples.
   

Key Questions

1. What are the defining characteristics of acids and bases?
   
2. How can we determine if a substance is acidic or basic?
   
3. What are the pH values of common household substances?
   
4. What are some important acids and bases in Saskatchewan agriculture and industry?
   
5. What is a neutralization reaction?
   
6. What are examples of common neutralization reactions?
   

Key Concepts

• Acids are substances that produce hydrogen ions ( H⁺ ) when dissolved in water. Acids are sour-tasting, good conductors of electricity, turn blue litmus paper red, and react with bases to form salts and water.
  
• Bases are substances that produce hydroxide ions ( OH ^- ) when dissolved in water. Bases are bitter tasting, good conductors of electricity, feel slippery, turn red litmus paper blue and react with acids to form salts and water.
  
• Indicators are substances that change colour at specific pH levels.
  
• The pH scale indicates the acidity or alkalinity of a solution. It is a logarithmic scale in which a change in pH of 1 indicates a ten-fold change in the acidity or alkalinity.
  
• A neutral substance has a pH of 7 and is neither acidic nor basic.
  
• Neutralization is the reaction between an acid and a base that produces a salt and water.
  
• A salt is an ionic compound that is composed of a cation from a base and an anion from an acid.
  
• Numbers can be used to convey important scientific information such as the relative strengths of acids and bases.
  
• Science and technology can be used to monitor the impact of acids and bases on the environment.
  

Pre-Instructional Questions

1. Do students know the difference between an acid and a base?
   
2. Are students able to identify examples of acids and bases in their daily lives?
   
3. Do students know how to use indicators to determine whether a substance is acidic or basic?
   
4. Do students know the pH of common household substances?
   

Suggested Teaching Strategies and Activities

1. Students should conduct an activity to determine whether common household substances are acidic or basic. Students could use a home-made indicator (e.g., boiled cabbage), litmus paper, phenolphthalein solution, pH paper, pH meter, or pH probe. A discussion of indicator technologies could highlight reasons why it is sometimes important to have very precise measurements of pH, while in other instances it may be sufficient to know that a substance is acidic or basic.
   
   
2. Students should develop a list of important acids and bases (e.g., sulphuric acid, lime, ammonia, phosphoric acid, sodium hydroxide), the characteristics of those chemicals, and where they might be used in Saskatchewan agriculture and industry.
   
   
3. Students could create a pH scale and place common substances at appropriate positions on the scale. Students should be made aware that the pH scale is logarithmic (i.e., a change of one unit on the pH scale represents a tenfold increase or decrease of hydrogen ion solution concentration). (NUM)
   
   
4. Students could bring samples of water (e.g., lakes, rivers, sloughs, wetlands, swimming pools, and kitchen taps) or soil (e.g., garden, school yard, compost pile, ditch, beach, sand dune) for pH testing . Teachers could integrate this activity with objectives in the Sustainability of Ecosystems unit.
   
   
5. Students could design an activity to investigate one or more characteristics of acids or bases, pH, or neutralization. For example, students might test the effectiveness of antacid tablets, test the acidity of various foods or cosmetics, or test the effectiveness of various bases in neutralizing a simulated acid spill.
   
   
6. Students could conduct an activity to neutralize an acid or a base. They should be able to explain what evidence supports the conclusion that water and a salt are the products of a neutralization reaction. Students should be able to discuss the role of an indicator in determining when the acid or base is neutralized.
   
   
7. Students could investigate practical applications of pH and neutralization by conducting research to answer questions such as:
   
   • What are natural and artificial methods of neutralizing acidified lakes?
   • How does lemon juice neutralize fish odors?
   • Why are fish only able to live in water within a certain pH range?
   • How is the balance of acidic or alkaline soils restored?
   • What is the purpose of baking soda in baking?
   • How do soda-acid fire extinguishers work?
   • How can an antacid settle an upset stomach?
   • Why is it important to know the pH of hair shampoos and conditioners? (IL)
   
   
8. Students should research a topic related to the effects of acids and bases in Saskatchewan agriculture or industry (e.g., soil chemistry, acid rain, industrial emissions, anhydrous ammonia storage and transportation). From their research, students could identify key issues and then develop a response to address all or some components of the issue. This response could take the form of a position paper, a structured controversy, a debate, a deliberative dialogue, or an action plan. Students can demonstrate giving and receiving feedback. (IL, PSD, CD 1.3)