Technology Idea
pH Survey
Probeware Lab

Background:

Many of the foods in your refrigerator are naturally acidic or basic. But which ones, and how acidic and basic are they?

By now you likely know that the lower the value of the pH reading, the more acidic the solution. For example, cranberry juice has a pH of about 3.5, while distilled water, which is considered neutral, has a pH of 7. Higher than 7, and the solution is basic.

In this lab, you will use a pH meter to find out the pH values of common household substances.

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The Questions:

What is the pH of various household substances?

Variables:

Identify the type of data you will collect to support your hypothesis and state the manipulated, responding and controlled variables in this investigation.

SAFETY REMINDER: Wear protective equipment while handling chemicals.

Materials:

  • pH sensor and link to computer
  • plastic cups
  • a variety of household substances, such as fruit juices, mustard, ketchup, eggs, milk, yogurt, vinegar, etc.
  • distilled water (if not available, substitute tap water)

Procedure:

Step 1:

For this activity, a pH sensor is used to determine the pH value of various substances. Connect the pH sensor to your computer - if you are using a USB sensor, your apparatus will look something like this:

Step 2:

Configure the computer software to collect pH data.

It would be wise to choose a digital display of the data, so you can clearly see the pH value of the substance:

Step 3:

Create a 3-column table for recording the substances to be tested, a prediction of the substance pH, and the actual measured pH. Fill in the substances and your pH predictions.

Step 4:

Place a small amount of the substance to be tested in a plastic cup. The pH sensor will work best and give most accurate results with substances that are in liquid form - therefore it may be necessary to add distilled water to the substance to be tested. For example, if you are testing thick BBQ sauce, add enough distilled water to give the BBQ sauce a thin consistency. A substance such as bread will have to blended thoroughly into distilled water to form a thin paste.

Step 5:

Put the pH sensor into the test substance and begin collecting data. Once the pH reading has stabilized, stop collecting data, remove the sensor, and carefully rinse it with distilled water.

Step 6:

Repeat steps 4 and 5 for all of the substances that you have to test. When you are done, clean the sensor and dispose of all substances as instructed by your teacher.

Forming Conclusions:

Based on the data you have collected, answer the following questions:

1. What is the pH of various household substances?
2. Were the results of your pH survey what you expected? Explain why or why not.
3. Search print resources or the Internet for other experimental pH values for the substances you have tested. For example here are two Internet links to pH values: Common pH values, MSDS hyperglossary.

Extending:

  • Discuss with your classmates how you might repeat this experiment to make the results more reliable. If you think improvements could be made, make changes to the procedure, and repeat the experiment.

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