Chemistry PBL 2 Project Group: 8 Members: Han Xin Ying, Jesslyn Ting Jie Sin, Lee Jia Wei, Phoebe Teoh Ern Wei Class: 4S4 Title: Use Natural Ingredients as pH Indicators Teacher: Pn. Chan Yoke Bee
Experiment Report Aim: To determine if red cabbage can be used as a pH indicator. Problem statement: Can red cabbage be used as a pH indicator? Hypothesis: Red cabbage can be used as a pH indicator. Variables: a. Manipulated : Type of solution b. Responding : Colour of solution after the pH indicator is added c. Fixed : Amount of solution and pH indicator Materials: Red cabbage, vinegar, lemon juice, isotonic beverage, hand wash, cleaner and water Apparatus: Knife, chopping board, strainer, bowls, cups, measuring syringe Procedure: 1. A small part of the red cabbage is cut out and chopped into smaller pieces. 2. The chopped red cabbage slices are put into a bowl and filled with 350 ml of boiling water. 3. The mixture is set for around 20 minutes until the red cabbage’s pigment is released. 4. The red cabbage is filtered out of the mixture and the remaining liquid is diluted with water. The solution will be our pH indicator. 5. 30 ml of vinegar is poured into a cup. 6. 20 ml of the pH indicator is added into the solution. 7. Steps 5 and 6 are repeated by replacing vinegar with lemon juice, isotonic beverage, hand wash, water and cleaner. 8. The observations are recorded in the table below. Results: Solution Colour of solution after the pH indicator is added Acid, neutral or alkali Vinegar Neon pink Acid Lemon juice Pink Acid Isotonic beverage Purplish pink Acid Hand wash Slight purple Acid Water Purple Neutral Cleaner Blue Alkaline
Discussion: 1. What are pH indicators? pH indicators are compounds that change colour in a solution over a range of pH values. The principle behind the function of an indicator is that it reacts with water to form hydrogen ions, H + , or hydroxonium ions, H3O+ . The reaction changes the colour of the indicator molecule. 2. How can natural ingredients be used as pH indicators? Many red, purple, and blue plants contain chemicals called anthocyanins, which are weak acids that dissolve in water and change colour in response to changes in pH. Because of this, plants with anthocyanins like red cabbage, blueberries and morning glories can easily be made into pH indicators. Beets containing betalain pigments can also be used as a pH indicator. 3. What are the importance of pH indicators? pH indicators help to determine the pH value of various solutions, which is important for controlling the availability of nutrients, biological functions, microbial activity and behaviour of chemicals. Due to this, monitoring or controlling the pH of soil, water, and food or beverage products is important for a wide variety of applications. Conclusion: The hypothesis is accepted. Red cabbage can be used as a pH indicator. Sources: Form 4 Chemistry Textbook, Chapter 6 https://youtu.be/oG-pNRVHsc4 https://www.thoughtco.com/definition-of-ph-indicator-605499 https://www.osc.org/diy-ph-indicators-kitchen-chemistry/ https://www.thoughtco.com/edible-ph-indicators-color-chart-603655 https://aperainst.com/blog/why-ph-is-important/