Explore, invent and apply
Yasmin Jayathirtha
The teaching of any subject has to be accompanied by practice and assessment. I have often wondered what makes a good exercise/problem for topics in chemistry. Formulae are hard to remember, the students are practically learning a new language, and so their vocabulary is limited. They may also need to remember descriptions of reactions. With all this, it is very hard to assess if a student is unable to answer because she doesn’t get the concept or because she cannot express it. Similarly, how do you assess the skills of science, observation, data collection, tabulation, and analysis? One can set exercises with instructions to be followed or provide data and ask for analysis – a chemical comprehension passage as it were.
This month, I would like to share some experiments that were used in a programme to teach reasoning skills for high school students. The experiments are a part of a set from Project SOAR (stress on analytical reasoning) and are based on Piaget’s ideas of learning. The experiments contain exploration, invention and application phases and do not need previous knowledge. Though these have been developed for high school students, I have found that students of class 7 onwards manage very well and find them enjoyable.
Name of the Experiment: The case of the Missing Labels
Materials
0.1 Mol dm–3 solutions of;
Hydrochloric acid (HCl), Silver Nitrate (AgNO3),
Ammonium Hydroxide (NH4OH), Nitric Acid (HNO3) – Set 1
Sodium Sulfate (Na2SO4), Sodium Carbonate (Na2CO3), Barium Chloride (BaCl2), Silver Nitrate (AgNO3), Lead Nitrate (PbNO3), Potassium Iodide (KI), Potassium Nitrate (KNO3) – Set 2
Per group
Stirring rod 1
Test tubes with stand 12
Reaction surface for micro scale chemistry 1
Droppers 22
Litmus paper
This exercise has three parts, exploration, invention, and application.
Exploration
The students (singly, in pairs, or groups) are given the solutions of Set-1, labelled. These will be in bottles for use with test tubes and labelled droppers for micro-scale use. They are shown the use of litmus paper to determine acid-base character and allowed to experiment, mixing the solutions together.
Invention
After the exploration, they should be asked to chart out how they would use the data collected to recognize the solutions.
Application:
The students should be given unknown Set-1. This consists of Set-1 without HNO3 and labelled with numbers instead of names. They should use the data collected and chalk out their plan for analysis to determine the identities of the unknown solutions.
After Set-1 is done, they can go on to big time! Set- 2 has seven solutions and will require more data collection and careful recording. The unknown Set-2 does not have potassium nitrate solution and they will have to determine the identities of six unknowns.
This has always been a big hit with students. They enjoy the detective work and find a genuine satisfaction in getting the identities correct.
The second experiment explores correlation between variables and again has three parts: exploration, invention, and application.
Name of the experiment: Shaking the blues
The students investigate the relationship between the amounts of glucose or NaOH in a solution to the time a blue colour persists.
Materials
Per set of students
1 mol dm–3 sodium hydroxide solution 300 cm3
1 g packets of glucose 7
100 cm3 graduated cylinder 1
250 cm3 conical flask 1
Rubber stopper to fit the flask 1
Timer 1
A small squeeze bottle of methylene blue solution (for all the sets)
Ask the students to take 50 cm3 of the sodium hydroxide solution and dilute it to 100 cm3. They should pour the solution into the flask, add a few drops of methylene blue solution and dissolve one gram of glucose in it. Stoppering the flask and shaking it will produce a blue colour that disappears after a while.
Exploration
The students should consider how to shake the flask and for what length of time. They should then time how long it takes for the blue colour to disappear. They should repeat the experiment after dissolving the second packet of glucose and continue till all the glucose has been used up.
The experiment should be repeated, changing the concentration of NaOH, using 100 cm3 of 1mol dm–3 NaOH and 1 g of glucose. The NaOH solution should be diluted to 0.75 and 0.25 mol dm–3 and timed again.
Invention
The students can analyze the data to be able to draw a qualitative or semi-quantitative relationship between concentration of glucose, NaOH and the time.
Application
They should consider other factors, such as time of shaking, method of shaking.
Reference
Project SOAR (Stress On Analytical Reasoning) Xavier University of Louisiana 1981
The author works with Centre for Learning, Bengaluru. She can be reached at yasmin.cfl@gmail.com.