Vernier Software and Technology
Vernier Software & Technology

pH

Figure from experiment 11 from Earth Science with Vernier

Introduction

Water contains both hydrogen ions, H+, and hydroxide ions, OH-. The relative concentrations of these two ions determine the pH value. Water with a pH of 7 has equal concentrations of these two ions and is considered to be a neutral solution. If a solution is acidic, the concentration of H+ ions exceeds that of the OH- ions. In a basic solution, the concentration of OH- ions exceeds that of the H+ ions. On a pH scale of 0 to 14, a value of 0 is the most acidic, and 14 the most basic. A change from pH 7 to pH 8 in a lake or stream represents a ten-fold increase in the OH- ion concentration.

Rainfall generally has a pH value between 5 and 6.5. It is acidic because of dissolved carbon dioxide and air pollutants, such as sulfur dioxide or nitrogen oxides. If the rainwater flows over soil containing hard-water minerals, its pH usually increases. Bicarbonate ions, HCO3-, resulting from limestone deposits react with the water to produce OH- ions, according to the equation:

{\text{HC}}{{\text{O}}_{\text{3}}}^{\text{ - }}{\text{  +  }}{{\text{H}}_{\text{2}}}{\text{O}} \to {{\text{H}}_{\text{2}}}{\text{C}}{{\text{O}}_{\text{3}}}{\text{  +  O}}{{\text{H}}^{\text{ - }}}

As a result, streams and lakes are often basic, with pH values between 7 and 8, sometimes as high as 8.5.

Objectives

In this experiment, you will use a pH Sensor to measure the pH of a body of water.

Sensors and Equipment

This experiment features the following Vernier sensors and equipment.

Additional Requirements

You may also need an interface and software for data collection. What do I need for data collection?

Standards Correlations

See all standards correlations for Earth Science with Vernier »

Experiment 11 from Earth Science with Vernier Lab Book

<em>Earth Science with Vernier</em> book cover

Included in the Lab Book

Vernier lab books include word-processing files of the student instructions, essential teacher information, suggested answers, sample data and graphs, and more.

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