PART I: Investigating Buffers
This is part of our Virtual Buffers Lab series: Understanding, Making, and Using Buffers.
This lab includes two short experiments to discover the properties of buffer solutions.
Learning Objectives
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Students will be able to… |
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Key Vocabulary
- Independent (Manipulated) Variable
- Dependent (Responding)
- Conjugate acid/base pair
- Concentration
- pH
- Buffer
Documents
- Click here for PDF of student worksheet. (HINT: It is helpful to use a split screen so you can see both this page and the data table at the same time.)
Part I: Investigating Buffers
Introduction
This activity is a lab investigation which addresses two scientific questions. A scientific question always asks how a manipulated, or independent, variable affects a responding, or dependent, variable. For example, a scientist could ask “How does the wingspan on a paper airplane affect how far it can fly?” In this case, the independent variable, what is being tested, is the wingspan; and the dependent variable, what is being measured, is how far it can fly.
Scientific Question Format: How does INDEPENDENT VARIABLE (IV) affect DEPENDENT VARIABLE (DV)?
Two scientific questions regarding acid-base buffer solutions will be investigated. An acid-base buffer solution (ie. buffer) is a solution that contains a conjugate acid-base pair–that is when the acid undergoes a reaction, it turns into its conjugate base; and when the base undergoes a reaction it turns into its conjugate acid.
Extensive knowledge about the chemistry of acids and bases or the concept of pH are not required to complete and learn something from this activity. However, a familiarity with terms is helpful.
Acids and bases are chemical substances that react with each other to form a more neutral substance. The acidity (acid) or alkalinity (base) of a substance can be determined by measuring its pH, which ranges anywhere on a scale between 0 to 14. Acids have a pH less than 7 and bases have a pH greater than 7. A pH of 7 is considered neutral.
Activity
Question 1: How does the concentration of buffer components in a solution affect the change in pH when a strong acid or strong base is added?
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Buffer Components |
IV- Concentration of buffer components |
DV- Change in pH when a strong acid or base is added |
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With 0.001 mol HCl |
With 0.001 mol NaOH |
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pH |
𝚫pH (final pH - initial pH) |
pH |
𝚫pH (final pH - initial pH) |
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HNO3 + NaNO3 |
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HC2H3O2 + NaC2H3O2 |
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NH4Cl + NH4OH |
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Analysis 1:
Describe the relationship between the concentration of the buffer components and the change in pH when an acid or base is added.
Question 2: How does the amount of the strong acid or strong base being added affect the change in pH of a buffer solution?
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Buffer Components |
IV- Amount of strong acid or strong base being added to buffer |
DV- Change in pH of the buffer solution |
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HCl |
NaOH |
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pH |
𝚫pH (final pH - initial pH) |
pH |
𝚫pH (final pH - initial pH) |
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0.1 M HNO3 + 0.1 M NaNO3 pH = |
0.001 mol |
pH = |
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pH = |
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0.010 mol |
pH = |
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0.1 M HC2H3O2 + 0.1 M NaC2H3O2 pH = |
0.001 mol |
pH = |
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pH = |
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0.010 mol |
pH = |
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pH = |
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0.1 M NH4Cl + 0.1 M NH4OH pH = |
0.001 mol |
pH = |
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pH = |
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0.010 mol |
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pH = |
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Analysis 2:
Describe what happened to the change in pH when different amounts of strong acid or strong base were added to the solutions.
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This lab was created with support from the Ren Research group at Purdue University with funding from the National Science Foundation grant NSF CHE 2102049.
