The class progress so far: The students are working on the task of identifying common salt out of many salts. They have explored "physical properties" of the given salts, like colour, solubility etc. They have been dealing with one parameter (physical property) and changing the value of it from colour, smell, solubility and shape (of the crystals under the microscope). They also have become aware of the fact that each of these values is what in an experiment is called "variable".

So their algorithm at the end of this phase looks like this:

A salt may be identified by looking for these variables 1. colour 2. smell 3. whether it is soluble in a) cold water b) hot water and 4. its crystalline shape.

After this there were no more values that could have changed for the given salts.

Exercise: A salt is given to them, (carbonate) They know it is a carbonate salt. They are given instructions to add an acid to it and test for the gas that is coming out. It is not hard to predict this, it is carbon dioxide gas.

Class discussion: To go back to the identification of common salt, what could you do?

Student response: Since the physical properties are already done, we need to look for more variables. Yes but how? If could make the sodium chloride "give out" some gas that we could test for? (this response was from one of the students, very tentative).

Teacher question: Why do you want it to "give out" a gas?

Student response: Then we could test for it

Teacher: So which gas could possibly come out of sodium chloride? (a list is drawn up on the board from the gases they have tested for in the lab. in earlier lessons. Nitrogen dioxide, oxygen, carbon dioxide, chlorine and bromine and iodine)

Student response: chlorine

Teacher: Why?

Student: There is no nitrogen, or oxygen or carbon or bromine or iodine in the formula NaCl. It does contain Chlorine, therefore it could be made to give out chlorine gas.

Teacher: How?

Student: by doing the same thing that was done to the carbonate salt i.e. by adding acid to it.

So now we are at this point. The students would then add acid to all the salts and test for the gas that comes out in each case.

At the end of this they would have explored 2 parameters, physical properties and chemical properties and explored ENV model for physical properties of 4 different values and one value for the parameter chemical property, namely add an acid and test for the gas that comes out.

After the end of this I intend to use another salt that they would be able to use their ENV model to identify.

Then I would introduce a third salt where the value of the chemical property (add gas and identify the gas evolved) would not help. So they would have to look for more parameters or variables.


# Alexander Sokol 2011-03-13 22:12
Interesting. Now it's much easier to follow - thanks, Krishna. A few questions / comments / concerns.
- it seems a lesson was a dialogue between you and some students. How many? Did others have to think? How do you know?
- I am always concerned when the algorithm looks the same for the whole class. Why?
- How do students 'fix' the strategy part? Where is it written down? By whome? When? How is it revised?
- When referring to 'their ENV model', what exactly do you mean? The algorithm?
# Krishnakali Gupta 2011-03-19 10:48
Yes, the lesson was a series of dialogue (broken up by the "experimentation" and "observation" bytes). There are a total of 10 students in Grade 8. I have summarised their part of the dialogue, although it developed from contribution by all of them.
The algorithm is messy at the moment (in my opinion). I am waiting for their lab report and will be able to comment only after they have come up with their writing and our discussion in the class (I have put this as my plan for the forthcoming lessons in Part 3)
they have been writing in their notebooks (they always take notes).
ENV model means something like this, they have been looking for "variables", are these variables (values) of physical or chemical nature (2 parameters?)
# Alexander Sokol 2011-03-20 08:58
Krishna, their algorithms are always messy. The question is if we succeed in getting them to regularly improve the algorithms. The most difficult thing, in my experience, is to get them to see it as an important part of learning rather than something they do for us (teachers).
Re their notes in notebooks. Are they able to find the algorithms there? Normally, all the notes in notebooks are organized chronologically. This is not very helpful for algorithms that need to be revised quite a few times. How do you solve this problem?
I am still not sure I understand about the ENV model. Have you actually introduced the ENV as a model to your students? I think there's a difference between the ENV as a model and variables as part of students' vocab. Do you see what I mean?
# Krishnakali Gupta 2011-03-20 22:47
Yes, ENV as a complete model, even though they have been introduced, has not been established in their heads. We are still in somewhat nebulous zone with only a partial view of the ENV, as in looking for variables. I see what you mean. However, the overall model that they have been actually working with (meta cognitive) level will emerge only after their write ups come in and we have a round of discussions to demonstrate how they have been using the ENV model.
Yes, their notes (at the moment) are chronological. As we (Deidre, youand I )discussed in the WP, I intend to get them to use a flexible folder where they could vary and change the sequence of these algorithms, or even strike out the ones that are not useful.
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