The lime water mystery

S Muralidharan

It all started with the lime water.

It was class IX of a reputed school. The just concluded Term one examination had a question related to the colour change that happens when carbon dioxide passes through lime water. The question paper had an illustration of the experimental setup, and students were asked to mention the expected colour change.

All students knew the answer– lime water turned milky in the reaction.

“How many of you have seen this reaction and colour change?” I asked.

The students looked at each other and started to murmur. They had not seen the reaction in the laboratory, but knew the theoretical outcome to score the marks.

This is a challenge for science educators– to make experiential learning the core of science teaching and theoretical learning the ancillary outcome. Though educational boards stress on the importance of experiential learning, nothing much has changed at the ground level.

Colour change of lime water, as an example of chemical change, is given in the syllabus of standards VI/VII in different boards.

To satisfy my curiosity, I met the science teacher of class VII.

“Ma’am, have you conducted the experiment of colour change of lime water?” I asked.

“Yes,” she said.

“Have you seen the colour change?  Did your students see the outcome?”

“No.”

“Why? What happened?”

“Sir, I carried out the demonstration, but the experiment setup didn’t show any colour change in the boiling tube containing lime water.”

“What might the reason be?”

“Probably, the concentration of carbon dioxide was not enough to change the colour.”

“Ok. As your students have no idea of the change in colour, how will you help them see the change?”

The teacher had no answer. I was convinced that she herself had not seen the colour change.  

We went to the lab, collected some lime water in a test tube. I asked for a glass blower. Using that carbon dioxide was blown into the lime water for some time. The solution bubbled and turned milky gradually. Obviously the teacher hadn’t blown long enough into the lime water and therefore didn’t get the desired result.

The teacher was glad to see the colour change easily. I asked her to call her students to the lab and demonstrate the activity.

Class VI-VIII science textbooks are designed in a way to teach science using activities. However, most teachers tend to ignore the activities and discuss science as theory, failing to meet the broad objectives of science learning.

A successful teacher is one who is ready to perform all the prescribed activities in the curriculum and also in designing their own activities going beyond the textbook. The author is Education Officer, Amrita Vidyalayam Tamil Nadu. He can be reached atsmuralivasudha@gmail.com.