Making pH Indicators

TITLE: Natural pH indicators

ABSTRACT:

From this experiment, we were created various pH indicators that can be used to test unknown solutions (household) to determine if they are an acid or a base. The substances in plant products such as red cabbage or turmeric react with acids or bases, resulting in changes at the molecular level which causes their colours to be different at different pH levels. All pH indicators, such as litmus paper, change colours depending upon whether they donate or accept protons. We pick selective natural dyes: red cabbage and turmeric to indicate specific pH levels based on their colour changes. The vegetables were chopped, smashed, and added with solvent to get the extract. Red cabbage shown very acidic solutions will turn anthocyanin a red colour. Natural solutions result in a purplish color. Basic solutions appear in greenish-yellow. The turmeric indicator changes colour more to basic condition. At the end of the experiment, red cabbage was suitable to used as a natural indicator.

INTRODUCTION:

There are many common household products and garden plants that can be used as pH indicators. Most plants contain pH sensitive anthocyanins, so experiment with other plants, too. Many of these natural pH indicators exhibit a broad range of colors. A pH indicator is a substance which has one colour when added to an acidic solution and a different colour when added to an  alkaline solution. In this experiment, we made our indicator from red cabbage and turmeric. This experiment explores the extraction of natural indicators from red cabbage and turmeric at which these natural indicators change colour. Turmeric also work by changing their colour with change in pH. The turmeric indicator changes colour roughly between 7.4 to 8.6. We used different indicators so that the result can be compare in order to accurately determine the pH.

MATERIALS:
 1)  0.1 M HCL solution, 0.1 M NaOH solution and 2-propanol were prepared.

    

                        

2) Vegetables: turmeric and red cabbage were preferred

                 

METHODS:

Extracting the indicator
1) Plant parts that were most pigmented was selected.
2) 10 mL of solvent and macerate was added to the macerated.
3) The filtrate from the macerated plant samples were filtered and collected.

Testing the pH range of the indicator
1)  13 test tubes from 1 to 13 were labeled.

2) 9.0 mL of distilled water was placed in all test tubes except #1 and #3.
3) The solutions in the acid range was prepared due to the following manner:
  a.  10.0 mL of 1.0 M HCL was placed in test tube #1. (pH=1)

  b. 1.0 mL of 1.0 M acid from test tube #1 to test tube #2 were transferred and mixed thoroughly. (pH=2)

  c. 1.0 mL of acid solution from test tube #2 to test tube #3 was transferred and mixed thoroughly.   (pH=3)

  d. 1.0 mL of the most recently diluted acid solution was transferred into the next test tube to make the    serial dilution of acid solution until pH 6.
4) 10.0 mL distilled water was added to test tube #7. (pH=7)
5) The solution in the acid range was prepared due to the following manner:

  a. 10.0 mL of 0.1 M NaOH was placed in test tube #13. (pH= 13)

  b.1.0 mL of 1.0 M NaOH from test tube #13 to test tube #12 were transferred and mixed thoroughly. (pH=12)

  c. 1.0 mL of the most recently diluted basic solution was transferred into the next test tube to make the   serial dilution of acid solution until pH 8.

6) The wells of a spot plate were labeled from 1 to 13. A few drops of each of the solution prepared in steps   3,4 and 5 were transferred to the corresponding well om the spot plate.

                

 7)  A few drops of the vegetable extract indicator were drop to each well. The pH was observed when the   indicator changes colour.

                      

Testing the pH of other liquids

Once the pH ranges of the indicators have been determined, they was been used in acid base titrations or to test the pH of household chemicals.

RESULTS:

Household	Indicator Colour		pH	Acid/Base
	Turmeric	Red Cabbage
Orange Juice	Concentrated yellow	Pink	1	Acid
Vinegar	Concentrated yellow	Pink	1	Acid
Tamarind	Concentrated yellow	Pink	1	Acid
Sauce	Concentrated yellow	Pink	1	Acid
Powder	Concentrated yellow	Light purple	4	Acid
Drinking water	Concentrated yellow	Light purple	7	Neutral
Shampoo	Light yellow	Light purple	10	Base
Dish washer	Yellow	Purple	11	Base
Toothpaste	Brick red	Greenish yellow	12	Base
Soap	Brick red	Greenish yellow	12	Base
Dynamo	Brick red	Greenish yellow	13	Base
Detergent	Brick red	Greenish yellow	13	Base

DISCUSSIONS:

Red cabbage contains a pigment molecule called flavin (anthocyanin). Very acidic solutions will turn anthocyanin a red colour. Neutral solutions result in a purplish color. Basic solutions appear in greenish-yellow. Therefore, it is possible to determine the pH of a solution based on the color it turns the anthocyanin pigments in red cabbage juice. The color of the juice changes in response to changes in its hydrogen ion concentration. pH is the -log[H+]. Acids will donate hydrogen ions in an aqueous solution and have a low pH (pH < 7). Bases accept hydrogen ions and have a high pH (pH > 7).

In this experiment, we were used the red cabbage extract as a pH indicator to test common  household substances and determine their pH levels. The chemicals responsible for the red colour in red cabbage and many other vegetables, fruits and flower petals belong to the anthocyanin family. We mixed  the  extract indicator with different household substances and saw a color change produced  by a pigment called flavin (an anthocyanin) in red cabbage. Through color changes, we are able to successfully identify the approximate pH of common  household substances using the table. The strength of the pH scale is determined by the concentration of hydrogen ions (H⁺) where a high concentration of H⁺ ions indicate a low pH and a high concentration of H⁺ ions indicate a high pH.  The pH scale ranges from 1 to 14 where 1 to 6  is classified as acidic, 7 neutral (neither a base or an acid) and 8 to 14 is classified as basic.

From the experiment, we observed that red cabbage is suitable natural indicators because it shown clearly the changes in colour either acid or base.  This indicator solution shown that the household substances  such as orange juice, vinegar, tamarind and source was an acid. This was due to the changes of colour from purple to pink when we mix them with the indicator . We prefer to use red cabbage extraction compare to turmeric in acid condition because the colour was clearly shown. The drinking water was showed in neutral condition with pH 7. While, most of the household like shampoo, dish washer, tooth paste, soap, dynamo and detergent were in basic condition. These were showed by the changes of the colour from purple to greenish yellow in red cabbage extraction and from yellow to brick red in turmeric extraction.That’s because turmeric contains a yellow pigment called curcumin, which is pH sensitive. Its molecules change shape in solutions of different pH. We can said that turmeric indicator can be use to test the substances that have the higher pH only which is base condition. From our observation there are no changes in colour for the substance in acid condition .  To test the pH of  base substance, we can used both  natural indicator because they were showed clearly changes in colours.

CONCLUSION:

In this experiment, we can conclude that red cabbage was more suitable to be used as a natural indicator. This is because the red cabbage shown clearly in acid and base condition compared to turmeric which is only more base. This conclusion was reached by observing the color change in the samples, the acid always turned pink and the base greenish-yellow. Overall the lab was interesting because of the red cabbage being an indicator.  

REFERENCES:

Cecie Starr, Christine A. Evers & Lisa Starr(2008).  Biological concept and applications.   United States : Brooks / Cole Cencage Learning.

Home and Garden pH Indicators. Retrieved on Mac 17, 2013 from http://chemistry.about.com/cs/acidsandbases/a/aa060703a.htm

Red Cabbage pH Indicator. Retrieved on Mac 17, 2013 from http://chemistry.about.com/od/acidsbase1/a/red-cabbage-ph-indicator.htm