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Identifying pH of Substances

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Identifying pH of Substances

Physical Science

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The pH scale is introduced and explored through experimentation using known solutions, universal indicator paper, and a color pH scale. Solutions are classified as acidic, neutral, or basic, depending on their reactions with the universal indicator paper, and a summary animation is presented.

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Now You Know

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

  • (LO1) Explain that pH is a measure from 0 to 14 that indicates whether a solution is acidic, neutral, or basic.
  • (LO2) Explain that a pH below 7 indicates that a solution is acidic, while a pH above 7 indicates that a solution is basic, with 7 being “neutral.”
  • (LO3) Explain that universal indicator paper turns increasingly red in lower pH solutions and increasingly blue in higher pH solutions.

Everything You'll Have Covered

Scientists use something called a pH scale to measure how acidic or basic a solution or substance is. pH means "potential hydrogen," and refers to the concentration of hydrogen ions (H+) and hydroxide ions (OH-) in a solution. A pH scale ranges from 0 for the most acidic solutions, to 14 for the most basic, or alkaline, solutions. Acids can donate hydrogen ions in a chemical reaction, while bases accept hydrogen ions in a chemical reaction. The more acidic a solution is, the closer its pH is to 0, while the more basic a solution is, the closer its pH is to 14, with 7 being neutral. The scale is exponential in nature, in that for every whole number increase, the concentration of ions increases by a factor of ten. In other words, an acid with a pH of 1 is ten times stronger than an acid with a pH of 2.

A color scale is also associated with the numeric scale, ranging from red at the most acidic level to purple at the most basic level. The color scale is used with universal indicator paper, or litmus paper, in determining how acidic or basic a solution or substance is. The color of the paper helps to determine how acidic or basic a substance or solution is by noting the correlation to the numeric pH scale.

Understanding pH, and being able to measure and modify it, has implications in many fields of science including biology, chemistry, medicine, and food. In addition, there are many applications to every-day situations, such as balancing the chemistry of a swimming pool, understanding the tastes of different foods, the use of detergents and soaps, and keeping a fish tank or pond balanced to best support aquatic life.

Tutorial Details

Approximate Time 20 Minutes
Pre-requisite Concepts acid, base, pH
Course Physical Science
Type of Tutorial Experiment
Key Vocabulary acid, alkaline, base