In continuation of the part two, the students carried out the same exercise for NaCl (adding acid and testing for the gas). they identified Chlorine gas (they were actually ecstatic doing this). They then declared they had identified (finally) the common salt. (I have given them the task of writing out a lab report of their finding. I will be looking out for their inputs under "hypothesis". This is because, in a lab report, this is the area least understood by students.

This is of course based on my earlier experiences with student writing. I would be interested to see whether their hypothesis has moved from being wild guess has moved to informed prediction) I am also planning to discuss their hypothesis in terms of the (explicitly stated) ENV model and make them aware of exactly how they have been using themi.e. to make them cognizant of this process.

However, I have also introduced the next task (taking away the fish). I cut short their celebration by telling them this, " Yes congratulations you can be sure that this is common salt. Halt. All you have actually explored is the chloride part. What if it is a chloride of another metal? For example, Potassium? would you get exactly similar results?"

While some (half the class about 5 students) felt very disheartened. However, the rest (another 5 have started thinking about OTHER chemical properties). I have left them at this point (to undergo a painful deadend kind of feeling). Next week, I want to open up with the same question. I have to introduce new "tools" (tools that would enable them to identify the positive radical in a salt). I do not know exactly how I am going to do it.


# Alexander Sokol 2011-03-20 09:03
Krishna, why introduce 'tools' rather than get them to create them?
# Krishnakali Gupta 2011-03-20 21:17
Yes, but I am expecting (hoping desperately)that they look in the direction of having the tools to identify metal radicals. Just before we broke up, at the end of the process I described above, one student wanted to know which gas would Potassium salts give off? Now that is completely off target. Because metal radicals do not give off gases at all. The entire process of their identification is based on 1. Flame test 2 precipitation reactions
I told the student to come back with some answer, which gas could he think of from a Potassium salt. So right now I would be happy to only see that they realize that they DO NOT have the tools (in other words, making the salt to give out a gas and then identify the gas is not going to work for metal ions)and formulate a pointed question, "how are metal ions analysed?" When I get this question, I can them teach a little theory about it. Here I would like to get them back to the second parameter (chemical properties) that they had been working with so far and have them realize that that is the direction to go. that is look for differences in their chemical properties, this time on the basis of metal ions. That is what I meant by introducing the tools.
So as I see it now there would be a 2 step process ahead
1. Feel the NEED for new tools
2. Teach them the theory that would then enable them to create a flow line or step by step model of identifying the metal radical.
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