PROJECT 1 : ACID BASE

Title :
Making a pH indicator using a red cabbage and flowers.

Objective : To make a pH indicator.

Introduction :

A pH indicator is a substances which has one colour when added to an acidic solutions and a different colour when added to an alkaline solutions. A pH indicator measures whether a substances (usually a liquid) is acidic or basic, and some indicators can also measure how acidic or basic it is. When the indicator comes in contact with a substances, the indicator’s colour corresponds to that substances’s approximate pH, which is a scale of zero to fourteen (with zero being the most acidic, seven being neutral, and fourteen, and fourteen being the most basic) that indicates the acidity or basicity of a substances.

Materials :

0.1 M HCL solution

0.1 M NaOH

2-propanol (isopropyl alcohol) / acetone / distilled water

Red cabbage

Flowers

Methods :

A ) Extracting the indicator

1. The most pigmented parts of plant was selected.

2. 10 mL of solvent and macerate was added.

3. The filtrate from the macerated plant samples was filtered and collected.

B ) Testing the pH range of the indicator

1. 13 test tubes was labelled from 1 to 13.

2. 9.0 mL of distilled water or deionized water was placed in all test tubes except 1, 7 and 13.

3. Solutions in the acid range was prepared in the following manner (Refer Table 1) :

a. 10 mL of 0.1M HCL was placed in test tube 1. (pH = 1)

b. 1.0 mL of 0.1M acid from test tube 1 was transferred to test tube 2 and mixed throughly. (pH = 2)

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

d. The making of serial dilutions was continued by transferred 1.0 mL of the most recently diluted acid solution to the next test tube until six acid solutions of pH 1 to 6 have been prepared.

4.10.0 mL of distilles waterwas added to test tube 7. (pH = 7)

5. A solutions of base was prepared in the following manner :

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

b. 1.0 mL of 0.1M NaOH from test tube 13 was transferred to test tube 12 and mixed throughly. (pH = 12)

c. The making of serial dilutions of the base from pH 12 to pH 8 was continued by transferred 1.0 mL of the most recently diluted basic solution to the next tube and mixed thoroughly each time.

6. The wells of a spot plate was labelled from 1 to 13. A few drops of each of the solutions prepared in steps 3, 4 and 5 was transferred to the corresponding well in the spot plate.

7. A drop or two of the flower/red cabbage extract indicator was added to each well. The pH at which the indicator changes colour was observed.

C ) Testing the pH of other liquids

1. Once the pH ranges of the indicators have been determined, its can used in acid-base titrations or to test the pH of household chemicals.

Results :

Discussion :

Red cabbage contains a compound called anthocyanin. Anthocyanin produces colour that varies dramatically depending on the pH of the solution. Depending on the levels of hydrogen ions in the solution, the anthocyanin undergo chemical reaction that changes its chemical structures, making it reflect a different wavelength of light and make them appear a certain colour. From pH 1 to 6, the colour of indicators range from dark pink to light pinkish purple. The colour is light purple at pH 7. From pH 8 to 13, the colour change from purple to blue, then to green, and lastly yellow.

Bougainvillea contains a compound called betalains instead of anthocyanin. Betalains is more stable than anthocyanin and its colour does not depend on pH. Therefore, there are not much colour changes when use as pH indicator. From pH 1 to 8, the indicator showed only slight different in light brown colour. The colour of the indicator is brown at pH 9 while yellow colour from pH 10 to 13.

The red cabbage indicators and bougainvillea indicators are used to test the pH of detergent, lotion, face cleanser, and sunblock. The detergent and lotion showed same pH when tested by both indicators. The pH of detergent tested by both indicators is pH 11. The pH of lotion tested by both indicators is pH 9. But the face cleanser and sunblock showed different pH when tested by both indicators. The face cleanser is pH 4 when tested with red cabbage indicators but is pH 5 when tested with bougainvillea indicators. The sunblock is pH 8 when tested by red cabbage indicators but is pH 10 when tested by bougainvillea indicators.

It is hard to determine the pH of the item tested by using bougainvillea indicators. This is due to the bougainvillea indicators does not showed significant colour different as the red cabbage indicators.

Conclusion :

As a conclusion, from this experiment that we had conducted we made two pH indicator from red cabbage and bougainvillea then tested it with few household chemical. The most acidic household chemical is face cleanser while the most basic household chemical is detergent.

References

Tanaka, Y., Sasaki, N. and Ohmiya, A. (2008), Biosynthesis of plant pigments: anthocyanins, betalains and carotenoids. The Plant Journal, 54: 733–749. doi:10.1111/j.1365-313X.2008.03447.x

Reflection :

1. TING MEE PING (D20141067055)
From this experiment, I know that red cabbage can be used as pH indicators. Red cabbage is a good pH indicator as it colour change significantly from acid to base. Thus, it is very useful and convenient tool to determine the pH of household item such as detergent, lotion, shampoo, face cleanser and other. Red cabbage extract will turn red or pink when the item is acid, purple when neutral, and blue, green and yellow when alkaline.

2. LENDRA NALAT ( D20141067021)

I have learned that cooperation and teamwork are really important to do all work, whether it is an easy task or difficult task. Besides, I have also learned about responsibility to do all works that have been given to me. This attitude I can apply in my daily life especially in my works. In this experiment, I also learned to always be careful especially when doing an experiment.

3. CHRIS ROXA ANGELLA SUPAIN (D20141067094)
From this experiment, I gain a lots of experience in making pH indicator from red cabbage and flowers. Before this I only watched red cabbage as pH indicator from video but from this experiment i experienced it by my self and it was very interesting. Beside that, in this experiment I was able to determine the pH level some of household chemical we bought. One of the catchy result for me is face cleanser was the highest acidity among the other household chemical and it was a new things for me. A suggestion from me is, we should do or try more experiment that use a household chemical so that we can apply it on our daily life.