The "Nature" of pH

Adapted for Logger Pro from an activity by the Concord Consortium
by Shawn Reintjes, The Science House, NCSU

Activity
Logger Pro Tutorial

Discovery Question: How acidic or basic are leaves?

 This activity enables you to explore acids and bases in the natural environment.

Thinking About the Question
How acidic or basic are leaves?

Chemicals are grouped together because of common properties. Acids are a group of sour chemicals. When a food tastes sour, like lemon juice or vinegar, it usually contains an acid. Bases have the opposite chemical properties of acids and feel slippery or soapy. Bases, like baking soda dissolved in water, have no strong taste.

Scientists have developed a scale to indicate how acidic or basic a solution is. You can test how acidic or basic a solution is by using a pH probe. The scale begins at 1, which indicates a very acidic solution, to 14, which indicates a very basic solution. A solution that has a pH of 7 (half way between 1 and 14) is considered neutral. In this activity you will test varying amounts of lemon juice in water, and baking soda in water, to understand the pH scale. After creating your scale, you will test leaves from different trees to determine their pH.

Your challenge is to investigate how adding different amounts of lemon juice to water will affect the pH, or acidity, of the solution. You will be able to use the pH probe to assist in your investigation. In your group spend a few minutes discussing and designing a procedure to be shown to your teacher.

The “Nature” of pH: Materials:

  • pH probe
  • baking soda (approximately 1 teaspoon per group)
  • graduate cylinder
  • lemon juice (25 ml per group)
  • clear plastic cup
  • water (approximately 300 ml per group)
  • small plastic bag that can be sealed
  • samples of different varieties of leaves
  • eye protection (optional based on school policy)

The “Nature” of pH: Safety

Do not taste any of the solutions used in this activity due to possible contamination of the containers or strength of the acids and bases.

The “Nature” of pH: Investigation I

Testing the pH of lemon juice

  1. Discuss an experimental procedure with your class. Before you begin your investigation make a prediction about the pH of water and how it will change as you add lemon juice.
  2. Create a spreadsheet to record the pH of the lemon juice (5 ml, 10 ml, 15 ml, 20 ml, 25 ml), baking soda (5 ml, 10 ml, 15 ml, 20 ml, 25 ml), and leaf (type 1, type 2, type 3) solutions that you will mix. Refer to Technical Hints to see how to create a spreadsheet.
  3. Obtain a clear plastic cup. Add 100 ml of water. Test the pH of the water by using the pH probe. Refer to Technical hints (click on Edit-Go To-Bookmark-Logger Pro Tutorial) to see how to use the LoggerPro software to measure pH. Record your pH in your spreadsheet. Transfer your data to your spreadsheet.
  4. Place 5 ml of lemon juice into your cup. Retest and record the pH of your solution.
  5. Continue testing and recording pH after adding additional amounts of 5 ml of lemon juice until you have added 25 ml of lemon juice total, to your water.

Answer Question 1 in "Analysis".

The “Nature” of pH: Investigation II

Testing the pH of a baking soda solution

  1. Fill a cup with 100 ml of water. Test the pH of the water by using the pH probe. Record your pH in your spreadsheet
  2. Place 5 ml (approximately 1 teaspoon) of baking soda into your plastic cup. Mix thoroughly. Retest and record the pH of your solution.
  3. Continue testing and recording pH after adding 5 ml of baking soda until you have added 25 ml of baking soda to your water.

Answer Questions 2-4 in Analysis.

The “Nature” of pH: Investigation III

Testing the pH of different kinds of leaves

  1. Obtain a small plastic bag. Place a small amount of water in the bag. Tear one type of leaf into small pieces. Seal the bag and carefully crush the leaves into the water. Continue crushing the leaves for 5 minutes being careful not to tear the bag.
  2. Test the pH of the leafy solution by using the pH probe pH. Record the names and pH of the leaf in your spreadsheet.
  3. Repeat the process for the remaining two types of leaves that you selected. Record their pH on the spreadsheet.

Answer Question 5 in Analysis.

Technical Hints

Creating a spreadsheet http://einstein.cs.uri.edu/tutorials/csc101/pc/excel97/excel.html#gettingstarted

Using a draw program to create a pH scale
http://kkc.k12.hi.us/tutorials/draw/index.htm

The “Nature” of pH: Analysis

Answer the following questions:

  1. What was the pH of the water? Using your data, describe how the pH of the water changed as you added the lemon juice? If you know that tap water is neutral (not an acid or a base) and lemon juice is an acid, what type of pH values indicate an acid?

  2. How did the pH of the water change as you added baking soda? How does the pH of water compare to the pH of the baking soda solution? If you know that tap water is neutral (not an acid or a base) and a baking soda solution is a base, what type of pH values indicate a base?

  3. How does the pH value of an acid compare to that of a base? The pH scale ranges from 1-14.

  4. Make a line that starts with the number1 and finishes with the number 14 in a draw program. Make sure that the number 7 is at the center. Refer to Technical Hints to see how to use a draw program to create a pH scale. Based on what you have learned from your investigations, label which values represent acids and which represent bases on your pH scale. Mark the numbers that represent stronger acids and stronger bases.

  5. Were your leaf solutions acids or bases? Place the names of your leaf selections at the appropriate location on your pH scale.

The “Nature” of pH: Further Investigation

 

Create and compare pH scales for pond, field, or forest locations by collecting and testing samples of organic substances (leaves, grass, bark, etc.) found at each site.*Investigate and relate how soils found around your environment vary in pH. Does soil pH have nay relationship to the plants that grow in it?

 

LoggerPro Tutorial for pH Activity

 

Open the Logger Pro program by clicking on the Logger Pro icon.

Next go to “File” on the toolbar and click “Open”. Find the book, Water Quality with Computers and open it. Click on Activity 02, “pH” to open the experiment file. You are ready to collect data.

To collect data, click the green arrow on the upper right corner of the toolbar. You may stop data collection at anytime by simply clicking on the arrow again. (Note: the button works like a toggle switch, It is green when it is off, but it is ready to collect data. It is red when it is running and actually collecting data.)

You can save your experiment files by going to “Experiment---Store Latest Run”. If you don not store after each data collection, the data will be overwritten and you will have lost it!

Return to Inquiry with Technology

 
     

Contact Us ____ Site Map____ Search____ Home _____Copyright 2006 The Science House