Acids and Bases
Investigation 3 – PreLab
Clean water is essential for everyday life. Water treatment plant and system operators ensure that the water pumped from rivers, streams, and reservoirs is clean and has a safe pH before it gets to your home.
This Investigation is designed to help you to answer the following Focus Question:
- What happens to the concentration of hydrogen ions (H+) when an acid and a base are reacted?
Note: This question is located in your SDR at the beginning and end of the Investigation.
As a class, read the Background(s) in the Investigation. When finished, discuss the following concepts as a class:
- The concentration of hydrogen ions (H+) in acidic solution can be decreased by diluting the solution.
- Another way to decrease the concentration of H+ ions in a solution is to perform a chemical reaction by dissolving both an acid and a base in water.
- Discuss the following equation illustrating that hydrochloric acid, like all acids, dissociates into H+ ions and a negatively charged ion like Cl– when dissolved in water.
- Discuss the following equation illustrating that sodium hydroxide, like all bases, dissociates into OH– ions and a positively charged ion like Na+ when dissolved in water.
- Discuss the following equation illustrating the neutralization reaction between hydrochloric acid and sodium hydroxide to produce water and NaCl.
- If the acid concentration is higher than the concentration of the base, then the H+ concentration will be high and the pH will remain in the acidic range.
- If the concentrations of the acid and base are equal, the pH will be in the neutral range, approximately 7.
- If the base concentration is higher than the acid concentration, then the H+ concentration will be very low and the pH will be in the basic range.
- Discuss the following equation describing the neutralization reaction. The reaction consumes two acid molecules and produces two water molecules because unlike NaOH, Mg(OH)2 possesses two OH– ions.
LEARN THE LabLearner LINGO
The following Key Term is introduced in the Investigation Background(s). It should be used, as appropriate, by teachers and students during everyday classroom discourse.
Note: The definition of this term 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
- Complete the Recall section in your SDR.
- What is the relationship between the pH of a solution and the concentration of hydrogen ions (H+)?
- When the pH is low, is the concentration of hydrogen ions (H+) low or high?
- When the pH is high, is the concentration of hydrogen ions (H+) low or high?
- How can the concentration of hydrogen ions (H+) be changed?
- This Investigation will help you to understand what happens to the concentration of hydrogen ions (H+) when an acid and base react.
- Play the video below. Remember to follow along with your SDR and make any notes that you think might be helpful to you in the lab.
- After the video, divide into lab groups to discuss strategy for the lab. For example, you may assign certain group members to perform specific functions during the lab.
Note: The purpose of the video is to allow you to anticipate the laboratory experience you will soon encounter. You 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.
For homework, you should review the Investigation and video in preparation for the Lab.