Properties of Buffers
By: The Flinn Staff
Item #: AP7663
Price: $67.80
In the Properties of Buffer Solutions Inquiry Lab Solution for AP® Chemistry, students attempt to design an ideal buffer solution effective in a specific pH range and to verify its buffer capacity.
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Product Details
What are buffers made of? How does a buffer work? Can a buffer be designed to be effective in a given pH range? Is there such a thing as an ideal buffer? The purpose of this advanced-inquiry lab kit is to design a buffer solution that will be effective in a specific pH range and to verify its buffer capacity.
Students begin the investigation with an introductory activity to explore the composition and pH of ideal buffers and compare their pH changes when a strong acid and base are added. Understanding the properties of buffers prepares students for the guided-inquiry challenge—to design a buffer that will provide effective protection at a specific pH and that will have the capacity to maintain the pH within a narrow range when prescribed amounts of acid and base are added.
Complete for 24 students working in pairs.
2024 CED Alignment:
Unit 8 - Acids and Bases
Topic 8.8 - Properties of Buffers
Topic 8.10 - Buffer Capacity
Description of the Lab
The purpose of this lab is to design an effective buffer with a specific pH value for a consumer or experimental biochemistry application. The investigation begins with an introductory activity to compare the properties of three acetate buffers containing varying ratios of HA and A–. The results provide a model for guided-inquiry design of an experiment to prepare a desired buffer and verify its properties and performance. Five different buffer “challenges” are presented—each student group chooses one.
Learning Objectives
- LO 8.8.A – Explain the relationship between the ability of a buffer to stabilize pH and the reactions that occur when an acid or a base is added to the buffered solution.
- LO 8.10.A – Explain the relationship between the buffer capacity of a solution and the relative concentrations of the conjugate acid and conjugate base components of the solution.
Skills Students Will Learn
- 1.B – Describe the components of and quantitative information from models and representations that illustrate both particulate-level and macroscopic-level properties.
In this lab: Students explain how added H⁺ or OH⁻ interacts with the buffer system at the molecular level.
- 5.F – Calculate, estimate, or predict an unknown quantity from known quantities by selecting and following a logical computational pathway and attending to precision (e.g., performing dimensional analysis and attending to significant figures).
In this lab: Students calculate expected and observed pH changes based on solution composition.
- 6.F – Explain the connection between experimental results and chemical concepts, processes, or theories.
In this lab: Students analyze their data to explain why the buffer resisted pH changes and how buffer capacity relates to conjugate species concentration.
Specifications
Materials Included in Kit:
Acetic acid solution, 0.1 M, 500 mL, 2
Ammonium chloride, 10 g
Ammonium hydroxide solution, 0.1 M, 500 mL
Buffer envelope, pH 7
Citric acid solution, 0.1 M, 500 mL
Hydrochloric acid solution, 0.5 M, 500 mL
Seltzer water, 8 oz, bottle
Sodium acetate, 30 g
Sodium bicarbonate, 10 g
Sodium dihydrogen citrate, 12 g
Sodium hydroxide solution, 0.5 M, 500 mL
Sodium phosphate solution, 0.1 M, 500 mL
Sodium phospate, dibasic, 20 g
Additional Materials Required (for each lab group): Distilled water, 0.01-g precision balance (shared), beakers, buret or disposable pipets, graduated cylinders, pH meter or paper (indicators, optional), spatula, stirring rod, medium test tubes, test tube rack, wash bottle, weighing dishes.
Additional Materials Required (for Pre-Lab Preparation): Bottles to store solutions, Erlenmeyer flasks, graduated cylinders, magnetic stirrer and stir bar.
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