Vernier Software & Technology

# pH

## 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.

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

## Earth Science with Vernier

See other experiments from the lab book.

 1 Introduction to Data Collection 2 Exploring Magnetism 3 Where IS North? 4 Searching for Iron Ore 5 Sea Floor Spreading 6 Soil pH 7 Soil Salinity 8 Soil and Acid Rain 9 Soil Temperature 10 Temperature 11 pH 12 Turbidity 13 Total Dissolved Solids 14 Water Treatment 15 Salinity of Ocean Water 16 Acid Rain and Its Effect on Surface Water 17 Freezing of Ocean Water 18 Desalination 19 Mapping the Ocean Floor 20 Are All Sunglasses Created Equal? 21 Comparing Sunscreens 22 UV Light and Clothing 23 Reflection and Absorption of Light 24 The Greenhouse Effect 25 Land and Sea Breezes 26 Relative Humidity 27 Dew Point 28 Wind Chill 29 Seasons and Angle of Insolation 30 Fossil Fuels 31 Solar Homes 32 Photovoltaic Cells 33 Wind Power P1 Air Temperature P2 Air Temperature and Relative Humidity P3 Ground Temperature P4 Barometric Pressure P5 Measuring Particulates P6 Weather Stations

### Experiment 11 from Earth Science with Vernier Lab Book

#### 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.