LabLearner—The Science of Learning
LabLearner—The Science of Learning

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Acids and Bases

Investigation 1 – PreLab

 

 

 

 

 

 

 

Back to Investigation 1

ZERO-IN

Italicized font represents information to be shared orally or physically completed with the students at this time.

The non-italicized font represents additional information included to support the teacher’s understanding of the content being introduced within the CELL.

ASK WHY

Remind students that acids and bases are all around us. They play an important role in the digestion of the foods we eat, the medicine we take, and even the cleaning products we use. Understanding these two classes of compounds can help us stay safe, healthy, and be informed consumers.

BRANCH OUT

Remind students that hematologists monitor the delicate balance between acids and bases in the blood. They know that if the acidity of the blood changes too much, the blood loses its capacity to carry oxygen, and, without oxygen, cells die.

GET FOCUSED

Inform students that the Investigation is designed to help them to answer the following Focus Questions:

  • What properties make acids and bases chemically reactive? Acids release H+ ions when they are mixed with water and bases remove H+ ions when they are mixed with water.
  • What is the relationship between the concentration of H+ ions in a solution and the chemical reactivity of strong and weak acids? Stronger acids are able to release more H+ ions when mixed with water resulting in a higher concentration of H+ ions. Weaker acids release fewer H+ ions resulting in a lower concentration of H+ ions.
  • What is the relationship between the concentration of H+ ions in a solution and the chemical reactivity of strong and weak bases? Stronger bases are able to remove more H+ ions when mixed with water resulting in a lower concentration of H+ ions. Weaker bases remove fewer H+ ions resulting in a higher concentration of H+ ions. ions when they are mixed with water and bases remove H+ ions when they are mixed with water.

Note: These questions are located in students’ SDRs at the beginning and end of the Investigation.

Note: These are succinct responses to the Focus Questions and are placed here for your reference at this time. Fully developed responses to the Focus Questions can be found on the PostLab page.

GO DEEPER

As a class, read the Background(s) in the Investigation. Have students read the information aloud or silently to themselves. When students have finished, discuss the following concepts as a class:

  • All acids, when dissolved in water, release hydrogen ions (H+). This results from the dissociation of one or more H+ ions from each molecule of acid. 
  • Hydrogen ions react with many different chemicals resulting in the significant reactivity of most acids.
  • A greater concentration of acid dissolved in water results in a greater concentration of hydrogen ions due to the dissociation reaction.
  • A weak acid dissociates less and produces a low concentration of hydrogen ions. A strong acid dissociates more and produces a high concentration of hydrogen ions.
  • Concentration is defined as how much solute, or in this case, how many hydrogen ions can be found in a specific volume of solution. This volume is usually one liter.
  • The concentration of hydrogen ions can be measured by using the pH scale. The pH scale extends from values of 1 to 14 and includes concentrations of hydrogen ion that are typically found.
  • A low pH defines a high concentration of hydrogen ions and a high pH defines a low concentration of hydrogen ions. 
  • All bases, when dissolved in water, release hydroxide ions (OH–). This results from the dissociation of one or more OH– ions from each molecule of base. 
  • Once the hydroxide ion dissociates, it reacts with any hydrogen ions present in the solution to form water. 
  • When a base and an acid are both dissolved in water, a neutralization reaction occurs. A greater concentration of base dissolved in water results in a lower concentration of hydrogen ions due to the reaction between hydroxide and hydrogen ions.
  • Hydroxide ions will extract hydrogen ions from other chemical compounds, resulting in the significant reactivity of bases.
  • A high concentration of base results in a low concentration of hydrogen ions due to the neutralization reaction.
  • A weak base dissociates less and results in a high concentration of hydrogen ions. A strong base dissociates more and results a low concentration of hydrogen ions.
  • The pH of a solution containing an acid and a base is a good measure of the neutralization of an acid. Adding more base results in more neutralization of the acid, a low hydrogen ion concentration, and a high pH. 
  • Due to its chemical properties, water can act as either an acid or a base, producing low concentrations of both hydrogen ion and hydroxide ion. 
  • The pH scale can be divided into three ranges. The neutral range is centered at a pH of 7. A pH lower than 7 is considered in the acidic range and above 7 is considered in the basic range. Even “pure” water contains some dissolved chemical compounds such as carbon dioxide gas that tend to either increase or decrease the pH.

Note: These concepts are integrated into the Background(s) and are used to deepen students’ comprehension of the big ideas.

 

LEARN THE LabLearner LINGO

The following list includes Key Terms that are introduced in the Investigation Background(s). They should be used, as appropriate, by teachers and students during everyday classroom discourse.

  • acid
  • ion
  • hydrogen ion
  • concentration
  • pH Scale
  • base
  • hydroxide ion
  • dissociate

Note: Definitions of these terms can be found on the Introduction page to the CELL.

Note: Additional words may be bolded within the Background(s). These words are not Key Terms and are strictly emphasized for exposure at this time.

SET FOR SUCCESS

  • Direct students to complete the Recall section in their SDRs. Student answers will vary.
    • What are acids and bases?
    • Which acids and bases are familiar to you?
    • Are all acids or bases strong or dangerous?
    • What does chemically reactive mean?
  • Inform students that they will investigate the properties of acids and bases by measuring the pH of some common acids and bases.
  • Inform students that they will use pH paper strips that contain four different chemicals that change colors when they react with hydrogen ions. The changing colors can be used to accurately determine the pH of a solution.
  • Play the video below. Stop to ask students questions or answer students’ questions when necessary. Remind students to follow along with their SDRs and make any notes that they think might be helpful.
  • After the video, direct students to divide into their lab groups to discuss their strategy for the lab. For example, they may assign certain group members to perform specific functions during the lab.

Note: The purpose of the video is to allow students to anticipate the laboratory experience they will soon encounter. Students should leave this PreLab session with a firm idea of what to expect and how to perform in the lab.

Note: Homework is posted below the video.

HOMEWORK

Tell students that they should review the Investigation in preparation for the Lab.