Natural Indicators: Rose Petals

Emily B, Alexis B, Melissa D, Gabbi L, and Mary M

Introduction

The purpose of our lab is to find a natural substance that acts as a pH indicator for acids and bases. Acids are substances that have a pH below 7, turn blue litmus paper red, and form hydrogen ions when they are dissolved in water. Acids can be classified as weak or strong acids. Weak acids are acids that release few hydrogen ions in an aqueous solution and strong acids completely ionize in a solvent. Bases are substances that have a pH above 7, keep blue litmus paper blue, and form hydroxide ions when in an aqueous solution. Like acids, bases can also be classified as weak or strong. A weak base is a base that releases few hydroxide ions in an aqueous solution and a strong base is a base that ionizes completely in a solvent. The pH of a substance is the value used to express the acidity or alkalinity of it. A pH indicator changes color depending on the pH of a solution because of the dissociation of the hydrogen ion from the indicator. The household items we are testing are: Fantastik (all-purpose cleaner), hydrogen peroxide (3%), distilled vinegar, strawberry-scented hand sanitizer, and contact cleaning solution. We predict that: Fantastik is a base, hydrogen peroxide is an acid, distilled vinegar is an acid, the hand sanitizer is a base, and the contact solution is a base.

Procedure

Part I: Making the Indicator

1.) Fill a small pot with water.

2.) Place on stove and wait until boiling.

3.) Peel the roses and place the petals into the water, stirring as you go. (We used four roses, but you can use however many you deem necessary.)

4.) Put lid on pot and let sit for ten minutes. Then continue checking the color of the water every five minutes until the desired dark red solution is reached.

5.) Place a bowl under a strainer and pour the pot's mixture (petals and liquid) onto the strainer and let liquid seep through.


Part II: Setting up pH Standards

1.) Label 7 test tubes with pH values of 1,3,5,7,9,11,13.

2.) Fill each test tube 1/4 full with standard pH solutions.

3.) Add 10 drops of the rose indicator to each tube and record the colors that correspond to each pH.


Part III: Testing the Samples

1.) Retrieve 5 test tubes and fill the separate tubes with each household substance.

2.) Add 10 drops of rose indicator to each test tube.

3.) Compare the colors of the household substances with the colors of the standard solutions from Part II. Estimate and record the pH of each solution.

Conclusions

  • After using red rose petals as a natural indicator, we learned that acids resulted in reddish pink colors, and bases resulted in more purple, green, and generally darker colors.
  • Our indicator is better at detecting bases. We know this because when we got higher on the pH scale (towards bases), the color of the indicator varied much more than when it was creating the pH standards for acids.
  • One problem we encountered during our experiment was that when we were testing our household substances, we felt like the contact solution and the strawberry-scented hand sanitizer didn't correlate to any colors that we created when making the pH standards. We "broke" our pH scale, so we had to estimate what two colors we felt the solutions were between.
  • If we were to do this experiment again it might have helped us to test all the known pH values so we could better match the colors of our household objects to the pH standard we developed.
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