Chemistry PBL Activity 2: Use Natural Ingredients as pH Indicators Name: Yeow Ee Shen Shawn Class: 4S4 Teacher: Pn Chan Yoke Bee Group Members: - Au Kai Yang - Goh Wen Jun - Ong Soon Aik - Keith Wong - Yeow Ee Shen Shawn
1. Introduction of pH Indicators pH indicator, also termed an acid-base indicator, is a halochromic chemical compound that is added in small amounts to a solution to determine the acidity or basicity of the solution visually. A pH value is determined from the negative logarithm of this concentration and is used to indicate the acidic, basic, or neutral character of the substance you are testing. Normally, the indicator causes the colour of the solution to change depending on the pH. pH values above 7.0 are basic, and pH values below 7.0 are acidic. Solutions with a pH value of 7.0 are neutral. 2. Importance of pH Indicators pH indicator is an important quantity that reflects the chemical conditions of a solution. The pH can control the availability of nutrients, biological functions, microbial activity, and the behaviour of chemicals. 3. How natural ingredients can be used as pH indicators? Natural ingredients such as plants that are red, purple and blue in colour 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 and blueberries can easily be made into natural pH indicators. 4. Description of the experiment conducted, including materials used and procedures followed The experiment conducted is to test out the acidity and alkalinity of different household items using natural ingredients as pH indicator. Therefore, we decided to use red cabbage as our natural pH indicator for this experiment. The few household items are listed below: Materials: Red cabbage, lemon juice, vinegar, drinking water, toothpaste, baking soda, turmeric, detergent, transparent plastic cups, soda, masking tape, marker and camera
Procedures: 1. Red cabbage is peeled and boiled in hot water. 2. Lemon juice, vinegar, drinking water, soda, baking soda, toothpaste turmeric and detergent are poured into different cups respectively. 3. Red cabbage water as pH indicator is slowly added into different cups filled with different solution. 4. The changes of colour in all different solution is observed. 5. The observation is recorded. 5. Results Types of household items Changes in colour pH results Lemon juice Pale yellow to reddish pink Acidic Vinegar Colourless to dark red Acidic Drinking water Colourless to purplish blue Neutral Soda Colourless to dark pink Acidic Baking soda Colourless to dark green Alkaline Toothpaste White to sky blue Alkaline Turmeric Remains unchanged Undefined Detergent Colourless to dark purple Alkaline From our experiment, we find out that our pH indicator, red cabbage water does not change the colour of turmeric solution. This is because turmeric solution is a basic indicator that does not change colour in neutral and acidic solution. Hence, we won’t observe any changes in colour when red cabbage water is poured into turmeric solution.
6. Discussion of the significance of the results obtained, and their relevance to real-world applications - The results obtained is vary in colour because different solutions have a different pH value which causes the colour to be different as well. For example, solution with a bright colour such as red has a pH value less than 7 which is acidic while a solution with a dark colour such as purple has a pH value more than 7 which is alkaline. Other than that, solution with a pH value of 7 are green in coloured because they are neutral. - Besides, we are also able to identify the level of acidity and alkalinity of a solution. For instance, lemon juice with a reddish pink colour is more acidic compared to soda which has a dark pink coloured. Hence, these pH indicators are very useful in our daily life as they are able to help us to identify which food is safe to consume and which are not by testing the acidic and alkalinity of the foods. Nevertheless, pH indicators also contribute to our environment and industries sector.