Chemistry Lab - Section 7: Acids and Bases

Basic Chemistry Lab Name:______Using Cabbage Juice as a pH Indicator

We discussed the relationship of acids and bases, as measured by pH, in some chemical processes. These processes occur in living things all the time, and are essential to the functions of life. In this lab we will experiment with various common substances to test their relative acidity or alkalinity.

Hypothesis:

Common household agents, which all have a natural origin, may be used to test and observe whether a substance is an acid or base. Chemical reactions will occur between acidic and alkaline substances.

Today, you will be using the juice from a boiled cabbage as a pH indicator to test solutions as to whether they are acidic or basic (alkaline). The cabbage has a pigment molecule known as flavin. It is an anthocyanin. Acidic solutions will turn anthocyanin red. Neutral solutions will keep/maintain the color purple. Basic/alkaline solutions will turn anthocyanin greenish/yellowish

Acids will donate (gets rid of) H + ions in an aqueous solution, and therefore have a low pH, or less than 7. Low H potential Bases will accept H+ ions in an aqueous solution, and therefore have a high pH, or greater than 7. High pH potential. Neutral on the pH scale is 7.

Procedures:

Step1. Select 4 containers at a time from the choices provided. Pay attention to the labels on the bottles. Put approximately (approximately 1 dropper full) of each solution in a reservoir. Remember which solution goes into each reservoir, labeling them if necessary. Return the solutions immediately for other people to use.

Step 2. Predict whether each of the solutions being tested is acidic, basic, or neutral. Using your pH chart, record a pH value beside each solution during your predictions.

Step 3. Record the color changes that you observe occurring in each reservoir as you apply 1 or 2 drops of the cabbage indicator. The color will tell you whether each solution substance is an acid , base or neutral.

Reaction Explanations:  The solutions that show no change of color are neither acids nor bases, remaining purple, and can be generally thought of as having a neutral pH.  Solution substances that turn the pH indicator red are acidic.  Solution substances that turn the pH indicator greenish/yellowish are basic/alkaline.

1 Basic Chemistry Lab - Acid-Base Reactions of pH indicators with Various Common Substances

Lab Results Recording Table

SOLUTION Predict Actual pH results SUBSTANCE ACID/BASE/NEUTRAL? Record variations Look on the label Record pH # you predict

After you. have recorded some of the solutions, investigate using the computer what they are used for

Jot note in the space below the solution.

2 Basic Chemistry Lab - Acid-Base Reactions of pH indicators with Various Common Substances

Lab Results Recording Table

SOLUTION Predict Actual pH results SUBSTANCE ACID/BASE/NEUTRAL? Record variations Look on the label Record pH # you predict

After you. have recorded some of the solutions, investigate using the computer what they are used for Be sure you clean up the work area first 

3 Reflection sheet for Cabbage Lab Science 10 Name:______

Directions: Reflect on your learning from today’s activity an respond below.