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

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Acids and Bases

Investigation 2 – PreLab

 

 

 

 

 

 

 

Back to Investigation 2

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 the health and success of plants depends on the soil. For this reason, soil scientists work closely with farmers to test the pH of their soil to see if it is within the desired range recommend for the field crops they are planting. If a desirable soil pH is not created and maintained, farmers will not be able to grow or harvest healthy crops.

GET FOCUSED

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

  • What is the relationship between the pH of a solution and the concentration of hydrogen ions (H+)? As the pH of a solution increases, the concentration of H+ ions decreases. An increase of 1 pH unit decreases the concentration 10 times. As the pH of a solution decreases, the concentration of H+ ions increases. A decrease of 1 pH unit increases the concentration 10 times.

Note: This question is located in students’ SDRs at the beginning and end of the Investigation.

Note: This is a succinct responses to the Focus Question and is 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:

  • The concentration of a solute is described as the amount of solute that is dissolved in a certain volume of solvent to make a solution.
  • Dissolving a large amount of solute in a certain volume would result in a high concentration.
  • Dissolving a small amount of solute in the same volume would result in a low concentration.
  • A less concentrated solution can be made by adding less solute or by diluting a more concentrated solution by adding more solvent.
  • Using a serial dilution, a series of less and less concentrated solutions can be made.

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.

  • solute
  • solvent
  • solution
  • dilution

Note: Definitions to 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 is the definition of concentration?
    • Can you think of some examples of different solutions that have different concentrations of a solute?
  • Use the example of the two different concentrations of cherry soft drink and how the more concentrated drink will be darker red and have a stronger cherry flavor than the more dilute drink.
  • Explain to students that the more concentrated drink has twice the dissolved solid as the more dilute drink.

Note: The following is a Teacher Demonstration.

  • To demonstrate the concept of concentration, fill the 1000ml graduated cylinder to the 1000ml mark. Add 1 drop of red food coloring, cover with a piece of plastic wrap and invert to mix.
  • Discuss the color of the solution describing its shade of red as pink or light red. Inform students that the concentration of the food coloring is 1 drop in 1 liter of water.
  • Fill the second 1000ml graduated cylinder to the 1000ml mark. Add 10 drops of red food coloring, cover with a piece of plastic wrap and invert to mix.
  • Compare the two solutions side-by-side. Discuss the color of the two solutions comparing the color of each, describing the color of the second solution as dark red. Inform students that the concentration of the food coloring in the second cylinder is 10 drops in 1 liter of water. This represents a more concentrated solution of the food coloring compared to the first solution.
  • Explain to students that in this Investigation they will measure the pH of different concentrations of hydrochloric acid to demonstrate the relationship between pH and hydrogen ion concentration.
  • 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.