Learning Objectives:

• Understand the definition of acid, base, pH, and buffer
• Understand how to measure the pH of solutions in several ways and how they compare
• Understand the concept of neutralization
• Understand how acids and bases behave in both water and buffer solutions.  

The chemistry of acids and bases is an important area of chemistry involved in everything from the way our bodies function to the synthesis of the latest drug molecules. From the shampoo you used this morning to the cup of tea you had at lunch, we are surrounded by solutions with specific pH values. In this laboratory, we will explore this important area of chemistry.  After learning important acid/base terminology, we will learn how to measure pH, identify acids and bases, and understand the importance of buffers.  

• Read the lab before coming to class.  The expectation at Chamberlain (CCN/CU) is that you come to class fully prepared for lab.
• Always dress properly for lab.  Be sure to wear closed toed shoes and long pants to lab.  In lab, wear your safety equipment including goggles, lab coat, and gloves.
• Always check with your instructor regarding proper waste disposal
• Listen carefully  to the professor’s instructions and work safely
• Always follow the rules outlined in the safety contract
• If in doubt of how to use a piece of lab equipment, ask your instructor.  Improper use of lab equipment can be dangerous or could damage lab materials.
• If you have any safety concerns, see your instructor.
• Use deionized water (DI water) in your experiments

Exploration 1: Terminology of Acid/Base Chemistry

Part 1: Complete the table of definitions below:

Part 2:  Identify each of the following as an acid, base, or salt

Exploration 2: Measuring pH

Part 1: Measuring the pH of solutions with a graded pH strip.

Materials: DI water, Unknown A, Unknown B, vinegar, lemon juice, 10% bleach, graded pH strips, 25 ml beakers, 25 mL graduated cylinders, tweezers, and a paper towel

Method:

Part 2: Measuring pH using a pH meter

Materials: Solutions from part 1, Squirt bottle of DI water, Kim wipes, magnet, pH meter, two large (250-500 ml) beakers

Method:

Question:

1. Unknown solutions A and B are 0.1 M solutions of either HCl or NaOH.  According to your pH measurements, which is which?
2. The pH of pure water is 7.  Comment on how closely your measured pH values from each measurement method compared to the expected value.
3. Which method was more appropriate for measuring the pH of the bleach solution?  

Exploration 3:  How does a strong acid effect the pH of water?

In this exploration, we will study how the addition of small amounts of a strong acid effect the pH of water.  

Materials: pH meter and waste/storage setup from exploration 2, disposable pipette, 100 mL graduated cylinder, 250 ml beaker, 25 ml beaker, 1 M HCl, DI water, stir bar

Method:

Questions:

1. How does the addition of HCl affect the concentration of the H⁺ ions present in the solution?
2. How does the addition of 1 M HCl effect the pH of the water?  
3. Graph the pH as a function of the drops of 1 M HCl added.  The pH should be on the Y axis and the drops on the X axis.
4. From the above graph, how would you describe the rate at which the pH value of the solution changed?

Exploration 4: How does a strong acid effect the pH of a buffer?

Materials: 0.2 M acetate buffer.pH meter and waste/storage setup from exploration 2, disposable pipette, 100 mLgraduated cylinder, 250 ml beaker, 25 ml beaker, 1 M HCl, DI water, stir bar

Method:

Part 4B: Measuring changes in pH of buffer using an acid

Questions:

1. How does the addition of 1 M HCl change the pH of the buffer solution?
2. Graph the pH as a function of the drops of 1 M HCl added.  The pH should be on the Y axis and the drops on the X axis.
3. From the above graph, how would you describe the rate at which the pH value of the solution changed?
4. Compare the magnitude and rate of pH change of 1 M HCl added to DI water vs. that of 1 M HCl added to your buffer solution.  What changes and similarities did you observe?  

Exploration 5: Comparing antacids

In this exploration, we will use simulated stomach acid to pit several antacids against each other to see which is the most potent.  (I like it!)

Materials: Tums, Alka-Seltzer, Graviscon , 0.36 M HCl, 25 mL graduated cylinder, 100 ml Beaker, stir bar, stir plate, mortar and pestle, pH strips or pH meter

Method:

Question:

1. In terms of acid base chemistry, are the active ingredient of antacids considered an acid or a base?
2. What is the cause of the change in pH of the simulated stomach acid?
3. Calculate the total amount of active ingredient required by multiplying the amount of active ingredient per tablet by the number of tablets used. Show your work in the space given below.
4. Compare your group’s findings with those of other groups to get an average amount of active ingredient and fill in the table below.
5. Below, construct a bar graph with the names of the active ingredient for each antacid on the X axis and the average amount of active ingredient required to neutralize the simulated stomach acid.  Which antacid required the least amount of active ingredient to counteract the simulated stomach acid?  Why is it more effective?
6. One base we could have chosen to neutralize HCl in stomach acid is Ca(OH)₂.  Show this reaction below, being sure to balance the equation and show all products.  

Reflection:

Reflect on 4 key concepts that you learned in this lab exercise.  Be specific in your answer (this should require 10-12 sentences).