Making our own pH indicators

Do you remember the years that you took intense examinations at school or college? The 10th standard year is a particularly tough one for students in India since so much importance is given to the Board Examinations which students take at the end of the academic year, in March. It seems as though, once a student enters 10th standard, their whole life revolves around these exams… they are signed up for coaching classes, and there is even more pressure than usual to study for school examinations, which often require large amounts of rote-learning.

At ALF, we too feel pressure to “complete” the syllabus ahead of time and prepare girls for these intense exams, but we are fortunate enough to have students and families who believe that learning is not a race, nor a relentless soaking up of information. This gives us the chance to explore the curriculum a little more, which we did a couple of weeks ago during our studies of acid-base chemistry, when we set out to make some natural indicators.  Girls were asked to bring in items known or thought to act as natural indicators, such as onion skins, beetroot, apple skin and turmeric. First, they had to crush the vegetable matter using a pestle and mortar.

Nidhi grinding up onion skin to extract the juice.
Nidhi grinding up onion skin to extract the juice.

Then, girls had to filter the mixture to extract the juice and leave all the solid parts (skin, roughage) behind.

Ankita and Alisha filtering their indicator.
Ankita and Alisha filtering their indicator.
Meghna filtering her indicator.
Meghna filtering her indicator.

Then, it was time to test each indicator in acid, alkali, and neutral solutions.

 

before
Here is the rose petal extract without any solutions added.
...and here it is, with a drop of a acid, water or  alkali added (left to right).
…and here it is, with a drop of a acid, water or alkali added (left to right).

This experiment was very simple and only took about 40 minutes to complete, but students enjoyed the chance to do “real chemistry”, and it was time well spent away from the demands of the textbook!

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