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ZingPath: Acids and Bases

Acid-Base Indicators

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Acids and Bases

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Lesson Focus

Acid-Base Indicators

Physical Science

Learning Made Easy

You will get to explore the properties of acids and bases and how to detect them. Also learn how to measure the pH of solutions.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • Realize that acidity of the environment can cause some compounds to change color,
  • Explain the practical applications of acid-base indicators.
  • Explain that each acid-base indicator has a specific endpoint.

Everything You'll Have Covered

Why do some compounds change color when their pH levels are measured?

~ Compounds change color based on how acidic or basic they are. The chemical dyes are called indicators. When the indicator reaches a specific pH value, it changes color.

A scientist is testing the pH of dishwashing soap. Typically, soap is known to have a pH between 7 and 9. Which indicator should the scientist use? Why?

~ The scientist should use two indicators to get an accurate answer. Bromothymol Blue has a pH range of about 6 to 7.6, and Phenolphthalein has a pH range of 8.3 to 10. Since soap has a known pH between 7 and 9, using both indicators will give the scientist the most accurate results.

How should a scientist decide which indicator to use to determine a specific pH value?

~ Each indicator has a specific end point that determines a specific pH value of a solution. Each indicator determines only one pH value because each indicator's end point value is stable.

a) The chemical dyes that change color depending on the pH of a solution are called indicators.

b) Indicators change color when they reach the end point, or a specific pH value.

c) Each indicator determines only one pH value because its end point value is stable.

c) Each indicator determines only one pH value because its end point value is stable.

A. Hand lens

B. Microscope slides

C. pH probe

D. Stereoscope

~ The correct answer is C. Measuring the pH level of the soil will determine whether the soil is acidic or alkaline. By using a pH probe, the gardener can determine the color of his/her hydrangea blooms by measuring the pH of the soil.

Tutorial Details

Approximate Time 2 Minutes
Pre-requisite Concepts Students should be able to define the following terms: acid, base, and chemical dye.
Course Physical Science
Type of Tutorial Animation
Key Vocabulary acid, base, chemical dye