An activity of Litmus paper test  

School: UPS Mora, Mori, Uttarkashi Zafar

As we (me and my colleague) had planned to meet science teacher of this school and to conduct an activity of showing acidic and basic nature of substances of daily use, by Litmus paper test. I tried to inform the teacher for our visit but unfortunately on all three times I called, a mechanical voice replied “The number you are trying is either switched off or out of coverage area, please try again later”. Anyway, we decided to visit school and perform activity with students and left for Mora from Mori, hanging on the back-rods of a vehicle, like stuntmen.

About the Village
Above on the hill beside the river “Tauns”, full of green fields, a village called “Mora” comes while moving some 7 to 8 Km from the remotest block Mori of district Uttarkashi, on the Purola-Tyuni road. Village community looks prosperous as many have agricultural fields and some have given their lands to a company of Rafting, known as In-Me. some, who are not very well enough, work with the company and in other occupations.
By going from the fields towards Mora Primary & upper primary school, there are chances of encountering with snakes, as this area is near to Thadiyar which people say is famous for snakes. Anyway I have neither met snakes there, nor do I want to.

In the school
School is full of plants, Chillies were ripen, a lemon tree is laden with young fruits and flowers of Sadabahar (Vinca Rosea) adding beauty near to school’s newly yellow-washed walls. A teacher was teaching in a class and other students were working by themselves in other classroom. The same teacher was also trying to manage students of PS, as one teacher was on leave and other was busy in CRC related works. That teacher told that one teacher in UPS is also on leave and other one has left for Mori to do some official work. At that time he was the only teacher in both schools. He added that while doing activity we should avoid sending students out of the classroom because recently two times Snakes had roamed in school premises. We ensured that we would do activities in classroom only.

About the Activity
Actually the activity is not new, it’s given in the 14th chapter “Kaise Kaise Padarth” of class 7th, science text-book of Uttarakhand state. It has also been included in ISTT module. It starts with a table where teacher had to ask questions about taste of different food material and then to generate some discussion on sour taste of certain fruits and other food materials.
Activity was based on the same chapter but I made certain changes in it considering 6th to 8th class students. After the taste the chapter was focused on differentiating acidic, basic and neutral substances from our daily life. For the activity I collected litmus paper strips from our science Kit and made a framework of activity and discussion.

The session of activity
I started Session by some ice-breaking activities because most of the students were not familiar with me. We did an introduction round in which everyone had shared her/his name with favorite fruit and sweets then we made voices of our choice.

After the introduction I asked names of various fruits from students and also asked about their taste. They gave me a long list of fruits including vegetables too. They suggested names of more than 25 fruits with different tastes but here in the table below, I have mentioned examples of few.

Fruit Taste (sweet) Taste (sour) Taste (other)
Guava (अमरूद) Guava
Pomegranate (अनार) Pomegranate Pomegranate
Orange (संतरा) Orange Orange
Mango (आम) Mango Mango
Banana (केला) banana
Walnut (अखरोट) Walnut
Cucumber (खीरा) Cucumber
Malta (माल्टा)
Chakotra (चकोतरा) Chakotra
Lemon (नींबू) Lemon
Tomato (टमाटर) Tomato Tomato

Here, they were confused in the concept of fruit and vegetable and when I asked “whether tomato and chilly are fruits or vegetables?” They looked slightly confused. I smiled and said okay “I am saying that Chilly and tomato are fruits but you can say them vegetables, we’ll talk on this someday”. I didn’t want to talk more about that debate because it’s a different topic to deal with.

Moving further I asked reason of sourness of fruits like Orange, Malta, Chakotra, lemon, etc. one student said “because their juice is sour”, I said “okay, then what makes their juices sour?”, the same student said “its nature of juice of these fruits”. Here I said that this nature of sourness in certain fruits occur because of presence of certain types of acids “Aml (अम्ल)”.

Actually when I introduced about acids, I found that students are not familiar with the textbook word “Aml (अम्ल)” what they know is “Tezab (तेज़ाब)”, which they have seen in their surrounding while people use it in cleaning washrooms, extracting gum from pine trees, etc. after collecting their previous understanding on acid I asked about base “क्षार”, they speak it “Chhar” locally. They expressed that they have seen Chhar in “Chulha (चूल्हा)” and they use it in washing clothes, utensils, etc.

Then I asked what other things you use in washing utensils and clothes, except Vim Bar and soap. One students said “Kamod mitti (कमोड मिट्टी)”. Kamod mitti is a type of soil which’s known as white soil here. After taking such example of basic substances (though that time I didn’t share more about nature of White soil, Vim Bar, Washing soap, Ash, etc.) but I said that these things show basic nature.

After this we collected examples of some acidic and basic substances, such as tamarind, lemon, washing soap, Ash, etc. At that time I asked students to tell how can we differentiate or identify that something is acidic or basic in nature? I said being sour is one nature but we cannot taste all acids and then I asked why? Students replied “because it’s dangerous” then I said there are various types of acids so the acid of fruits is very different from that acid which u see in your houses for extracting gum of Pine (चीड़ का लीसा).

Then I asked students “how many of you have seen Argaar (wasp) or ततैया/बर्र?” Everyone raised hand, then I asked “what things do we use for treatment of its bite?” Students shouted “we rub iron”, “we use white soil”. I said that wasp injects a type of acid in our body and something of basic nature we use to neutralize its effect. That time I tried to explain them Neutralization by giving example of gravy’s mark on the cloths and how we try to remove by washing it with soap. Here, Manoj Ji also added an example of acidity removing tablets or solutions. Off course at that level I was not trying to go deep into the Ph and all but I gave example of neutral substance “water”.

Here a decision of performing an activity to know the method of finding basic and acidic nature, had been collectively made by the group. I introduced Litmus paper to them and said this paper can tell us which substance is acidic and which one is basic in nature. a

About Litmus paper
To introduce litmus paper I asked “how many of you have seen or used Patthar ki Mehndi (local name of lichen)?” Everyone had a knowledge about that, and then I introduced the term Lichen to them for the same. I added that from a type of lichen’s extracts these papers are made. These litmus papers are basically indicators (सूचक) which tell us acidic and basic nature of substances and today we’ll use them for our experiment.

The Litmus paper test
Though it was a group exercise but students performed each testing individually. Students one by one went near to the table where all samples/solutions were kept and they tested the nature of solutions by dipping litmus paper.
The table given below was supposed to be filled by the students after testing given samples/solutions. When they filled it, then it looked as it’s given below:

Solution Effects on blue litmus paper Effect on red litmus paper
Tomato Juice with  water Turned red, red, red, red. No eff (X), X, X, X
Water X, X, X, X X, X, X, X,
Lime juice with water Turned Red, Red, Red, Red X, X, X, X
Salt-water X, X, X, X X, X, X, X
Vim bar water solution X, X, X, X Turned blue, blue, blue, blue

The table shows result of a group of four students. In most of the cases students performed activity carefully and they found that blue litmus paper turned red in two cases; one of lime-juice and another of tomato juice. On other samples/solutions, blue litmus showed no effect.
Every student had performed testing of each sample and they filled their tables according to their findings. In two three cases salt-water turned blue litmus paper slightly red (surely it was because of error but I accepted their observations and noted on the board).
At the end when students performed same activity with Red litmus paper, they found that Red litmus paper turned blue only in the case of Vim Bar-water solution. Now that was the time to summarize all extracts and findings of activity. At the end because of repeated observations students understood that blue litmus turned red when sample was acidic and Red turned blue when sample was basic in nature. Perhaps they will remember results of this repeated exercise.


About experimental error
As mentioned above some students got results different from expected ones. Thus, I gave example of one student whose blue litmus turned red in salt water and we all had observed that he had dipped his fingers in lemon water. I connected this example with precautions of experiments and suggested avoiding touching, tasting, smelling samples during experiments.

We concluded that we got different results in some cases because of experimental errors. I gave a brief to students on using samples and apparatus fully clean in experiments and also washing apparatus, table, etc., after the experiments.

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