pg. 1 Chemistry Form 4 PBL Project 2: Use Natural Ingredients as pH Indicators Name: Koh Jia Yu Class: 4S3 Teacher: Pn Chan Yoke Bee Table of Contents Title Page 1.0 – Introduction to pH indicators 2 2.0 – Importance of pH indicators 2 3.0 – Natural ingredients as pH indicators 2 4.0 – Experiment 3 5.0 – Discussion 4
pg. 2 1.0 Introduction to pH indicators A pH indicator is an acid-base indicator that exists as liquid dye and dye-infused paper strips. A pH indicator changes colour in solution over a narrow range of pH values. A pH indicator is used to indicate the acidic, basic (alkaline) or neutral character of the substance that’s being tested. pH indicators are added to various solutions to determine the pH vale of those solutions. The liquid form of pH indicators is usually added directly to solutions, while the paper form is dipped into solutions and then removed for comparison. Some indicators like red/blue litmus paper change from one colour to another, while others like phenolphthalein, change between coloured and colourless states. pH indicators are usually weak acids or weak bases (alkaline). 2.0 Importance of pH indicators pH indicators are important as it is used in various fields in our modern society. Those include agriculture, where pH indicators are used to test the soil’s acidity to determine if suitable for planting; the food industry, where pH indicators are used to measure the quality of food, to prolong the shelf life of food and to control the taste along with other properties of food and water treatment, where pH indicators are used to monitor the pH value of drinking water which lies between 6.5 and 6.8, and wastewater, which the pH value is controlled so that desired chemical reactions can proceed efficiently. 3.0 Natural ingredients as pH indicators Apart from pH indicators normally used in lab experiments, such as the universal indicator, and red/blue litmus paper, natural ingredients can also be used as pH indicators. Many red, purple, and blue plants contain a water-soluble pigment called anthocyanin. Anthocyanin is a weak acid that dissolves in water and changes colour in response to changes in pH values. Because of this, plants with anthocyanin like red cabbage and blueberries can easily be made into pH indicators.
pg. 3 4.0 Experiment Aim: To test the acidity or alkalinity of different household items using a pH indicator that is made from natural ingredients. Problem statement: What is the acidity or alkalinity of different household items? Materials: Vinegar, lemon, laundry detergent, red cabbage, baking powder, hand sanitizer Apparatus: Knife, spoon, pot, clear containers Hypothesis: Vinegar and lemon are acidic, hand sanitizer is neutral, baking powder and laundry detergent is base (alkaline). Variables: (a) Manipulated: Types of household items (b) Responding: Colour of solution (c) Fixed: Amount of red cabbage solution Procedure: 1. 50 ml of vinegar, lemon juice, laundry detergent-water solution, baking powder-water solution and hand sanitizer were added into clear containers. 2. A red cabbage was cut into small pieces and boiled in a pot of water. The red cabbage was boiled for 5 minutes. 3. The red cabbage juice was poured out from the pot and cooled. 4. After it was cooled, the red cabbage juice was poured into a clear container. 5. 50 ml of red cabbage juice was added into the containers which contained vinegar, lemon juice, laundry detergent-water solution, baking powder-water solution and hand sanitizer. 6. A spoon was used to stir the solution. 7. When the reaction was complete, the observations were recorded. Results: Household items Colour of solution pH value Acid/Alkali Vinegar Pink 2-3 Acid Lemon juice Pink-red 3-4 Acid Hand sanitizer Violet 7 Neutral Baking powder Blue-green 8-9 Alkali Laundry detergent Green 10-11 Alkali Conclusion: Hypothesis is accepted. Vinegar and lemon are acidic, hand sanitizer is neutral, baking powder and laundry detergent are base (alkaline).
pg. 4 5.0 Discussion 1. Can red cabbage be used as a pH indicator? Explain how it works as a pH indicator. Red cabbage can be used as an indicator after boiling it in water for several minutes and extracting the juice after cooking it. Red cabbage contains a water-soluble pigment called anthocyanin that changes colour when it is mixed with an acid or a base. The pigment turns red in acidic environments with a pH less than 7, the pigment remains as violet in neutral environments with pH 8 as it does not undergo any change, and the pigment turns bluishgreen in alkaline environments with a pH greater than 7. As shown in the experiment, once the household items have contact with the red cabbage juice, the colours of the solutions have changed to either pink, violet or blue-green according to their pH values. 2. Describe the observations that you have obtained from this experiment. It seems that the red cabbage juice, which acted as the pH indicator in this experiment, had a very quick reaction towards the household items used for testing. Also, the colours of the household items tested were very vibrant and clear. 3. What is the relevance of this experiment to real-world applications? Household items that are available in our houses are all made up of either acid, alkali, and neutral substances. By having natural pH indicators around us, it makes it easily accessible for people to undergo experiments at home to test the pH value of substances that is tested. pH testing is important in our daily lives as our digestive system works in the pH range of 7 to 7.8, therefore for the proper functioning of our digestive system, it is important to maintain its pH value. Plants that we normally glow also require optimum pH, which lies between 6.3 to 7.3 for their growth, hence it is also important that the pH value of the soil to be checked frequently. Color Pink Dark Red Violet Blue Blue-Green Green-Yellow pH 1-2 3-4 5-7 8 9-10 11-12 Acid/Alkali Acid Acid Acid/Neutral Alkali Alkali Alkali