Towards a just, equitable, humane and sustainable society

Acids and Bases


Activity based learning have always helped in gaining better understanding of subjects. This is an educational task that involves direct experience and participation of children. This methodology was successful for teaching Acids and Bases to my children of class VII. Before introduction of any topic it is necessary to know how much children are aware of the same, so I began the class by checking their prior knowledge by asking them a few questions,

Teacher: How can you differentiate between an acid and a base?

Children: That which tastes sour are acids and bases are soapy and tastes bitter. 

Teacher: What are natural indicators? 

Children: Hibiscus, Turmeric

Teacher: What colour changes do we observe in different medium?

Student: Started to think…

 

Our own laboratory

Handling glassware and chemicals is an important skill in chemistry to be nurtured through careful monitoring and guided instructions. Students were demonstrated -how to use the test-tube, what should be done if chemicals spill over hand etc.  

Science Magic:

Initially children were given chemicals like hydrochloric acid, sodium hydroxide to test their characteristics using phenolphthalein indicator. Phenolphthalein is colourless in acid solutions and turns pink in basic solutions. Children were amused to see the colour change. Then the children were asked to mix the contents in the two test-tube and observe the changes. They were surprised to see the pink colour of the base disappeared.

“What happened to the colour? Why did the colour change?”

“The colour changed because the acid ‘killed’ the base in the solution”

“So what is the resulting solution? An acid base or a neutral substance?”

“Acid!!”

Now children were provided with pH paper and asked to test the nature of the solution. The pH paper indicated the substance to be neutral. 

“So what is a neutral substance?”

“That is neither an acid nor a base, for example water, salt”

Based on their response it was highlighted that mixing an acid and a base gave us a new substance that is neutral. We cannot obtain the initial acid and base using physical properties, and hence a chemical change has occurred  

 Based on the observations obtained difference between physical property and chemical property was discussed. 

Then the discussion was directed towards acids and bases within our body, responses were varied but since they would have studied digestive system in the previous classes a recap was be required to elicit that our stomach contains acid. 

Children are familiar with ENO™ advertisement, they are asked how do they get stomach aches, they said by over eating chocolates, eating with dirty hands etc. then building on the responses, acidity is introduced and told that when the amount of acid increases in our stomach, we feel some irritation and inflammation, to relax this we take in ENO™. The children were asked to predict the characteristics of ENO™ and then encouraged to test and check their predictions. 
 

Teacher: Stephen S, TGT GHS Mangalam

 

Grade: 
7

Subject: 
Science

Term: Term 2