AUTHOR: BURCU DENİZ
While examining some substances in our environment, we examine them in two groups as acids and bases. Substances that donate H+ ions in aqueous solutions are called acids. The flavours of the acids are generally sour and acids are caustic. For example:
HCl: Hydrochloric Acid-spirit of salt, H2SO4: Sulfuric Acid-Olive oil- ,
HNO3: Nitric Acid- vitriol, CH3COOH: Acetic Acid-radical vinegar,
CO2: Carbon dioxide, SO2: Sulphur dioxide.
Acids are also involved in the structure of food and beverages in daily life. Vinegar contains Acetic Acid, Yogurt: Lactic Acid, Lemon: Citric Acid…Substances that donate (OH)– ions in their aqueous solution are called bases. Usually, bases have hydroxide (OH)– ions in their structure. The bases are usually hot in taste. It gives a slippery feeling to the hand. NaOH: Sodium Hydroxide -Sud Caustic, Ca (OH)2: Calcium Hydroxide-Slaked Lime, KOH: Potassium Hydroxide-Potash Caustic, NH3: Ammonia. There are also bases in the structure of food and beverages in daily life. These include chocolate, mayonnaise, baking powder, baking soda… Bases are generally used in the construction of cleaning materials. For example; laundry detergent, dishwashing liquid, bleach…When detecting acids and bases, it is dangerous to look at their taste, smell them, touch them. Because there are very dangerous acids and bases. That’s why we use reagents to detect them. Some of these separators are:
- pH meter: We call substances ‘0 -7’ as acid, pH ‘7’ neutral, and pH ‘7-14’ as a base.
- Litmus paper: If the aqueous solution turns blue litmus red, it is acid. If the aqueous solution turns red litmus blue, it is base.
- Phenolphthalein: The colour of the substance dropped with phenolphthalein becomes pink in the base. It does not react with acids.
- Methyl orange: it becomes red with pH values less than 4.4 and It becomes yellow in values higher than 6.2.
Apart from these reagents, there are many substances that exist spontaneously in nature and serve as reagents. Some of them are:
- Hydrangea Plant Indicator: Hydrangea, a plant, blooms in different colours depending on the acidity or alkalinity degree of the soil in which it grows. If the hydrangea plant grows in an acidic place, it will bloom in blue. If it grows in a basic place, it will bloom in pink.
- Red Cabbage Juice Indicator: After the red cabbage is carefully cut into small pieces, hot water is poured over them. After pouring hot water, the red cabbage is kept at room temperature for a certain period of time, and then the mixture is filtered with a strainer. After the straining process is complete, we have a solution of red cabbage juice. This solution turns red if an acidic substance is dropped, and if a basic substance is dropped, the colour turns from purple to blue.
- Turnip Juice Indicator: When we use turnip juice as an indicator, it turns dark pink in interaction with acid substance and green in interaction with base substance.
- Cherry Juice Indicator: After separating the cherries from their seeds and crushing them in a mortar, the cherry juice we produce turns into light yellow if we drop a basic substance, and if we drop an acidic substance, it turns pink.
Using this power of nature, we wanted to determine whether the substances in our house are acids or bases. We used turnip juice as a reagent in our experiment. Students were subjected to a pre-test on this subject via Kahoot. Then, students drip the materials we determined into turnip juice and observed the colour changes. As a result, they learned whether the products we use in our home are acid or base.
- Age of Students: 13-14
- Number of people: 40
- Duration: 40 minutes
- Date: 22.04.2021
- Increasing awareness of acid-base reagents in nature.
- Recognizing whether products used at home are acidic or basic.
- Becoming conscious about using the resources in nature in the right way.
- Making students more sensitive to their environment.
Can we use products in nature as acid-base separators?
TO ACHIEVE THE GOAL
Project Based Learning, STEM Learning is used.
Making experiments with students in an online activity, pre-test and post-test application via Kahoot. Materials that students should prepare for this experiment:
- Lemon juice
- Dish detergent
- Washing powder
- Baking soda (baking powder)
- Gloves – Mask
Students solved the pre-test on the acid-base subject via Kahoot. Then the event started. Students filled half of each teacup with turnip juice. In order to prevent possible confusion, they made a note on the glass which ingredient they put in which glass. They observed the colour change by putting the materials selected for the experiment one by one into each glass, respectively. They wrote these colour changes on their notebooks.
Students saw that turnip juice obtained from the turnip plant found in nature is a natural reagent and can be used to determine whether substances are acids or bases. In the next step, this experiment was repeated using other reagents found in nature to develop the experiment.
The students were held the final test via Kahoot.