Wednesday, April 16th, 2014

New Equation writing: Does balancing and removal of choice signal a real change?

Having now got official word and examples from the test committee (thank you!!!!!), I am delighted to be able to move on to more positive thinking about the new question #4. I am curious about the new requirement to balance. The way I see it is this; I think that this may eliminate (or at least make very difficult) several equations from the (traditional) list. For example I think students will find it VERY difficult to do meaningful balancing of many complex redox reactions. Consider complex redox reactions that involve hydrogen peroxide, disproportionation, non-metal halides in water and it even puts organic combustion reactions in a slightly different light (previously a guaranteed 2 out of 3 points, now not so quick). Even things that are very common like the use of dichromate (VI) and manganate (VII) in redox chemistry that are relatively easy to balance will take on a whole new light for some kids. I think what I am trying to say is that the balancing of many of the traditional equations in question #4 will be beyond many students. It so happens that the 2006 set do not really reflect this concern as most of them are equations that do not fit into this “difficult to balance” category. I think this may be a window into the future – I guess we’ll see! In addition, with the removal of choice I feel we are bound to see a trimming of the traditional list to a more manageable set of “traditionally asked” equations.

Comments

  1. diverdown555 says:

    While I agree that balancing the redox equations will be a change, the reaction you spoke of, dichromate VI and permanganate VII are really classic reactions that get to one of the oldest and most “real world” uses of chemistry, determination of metals in ore. Even the combuation of alkanes will require change, but would you really feel you had taught a student a real chemistry course if they could not balance those reaction at almost the drop of a hat? I surely would not. I think it is probably a good change, and at least now students will have to be exposed to some of these reactions that they could have gotten away without ever seeing or doing for themselves ( example: actually titrating iron samples with permanganate.) And I would want this to be a discriminator among the best students. I saw many students coming into freshman chem lab with the idea that “chemistry was easy in high school, so this will be easy too.” they quickly found out, after all the chemistry they had in high school was blown through by a professor in 3 weeks. It is also another way to indirectly mandate lab activity or as I said at least Demos which would be better than just telling students what to expect as observations. Balancing equations is one of the most fundamental concepts we use, and since on the entire exam they are given balanced equations, they should be made to demonstrate their prowess at it.

  2. >dichromate VI and permanganate VII are really classic reactions that get to one of the oldest and most “real world” uses of chemistry, determination of metals in ore

    Agreed, but so what?

    >Even the combuation of alkanes will require change, but would you really feel you had taught a student a real chemistry course if they could not balance those reaction at almost the drop of a hat? I surely would not.

    Well, that’s a different question completely and it cuts to the philosophical core of what we are trying to do. I bet that there are a multitude of acceptable answers to that question!

    >It is also another way to indirectly mandate lab activity or as I said at least Demos which would be better than just telling students what to expect as observations.

    I COMPLETELY disagree. If you want to mandate lab activity SET A LAB EXAM!

    >Balancing equations is one of the most fundamental concepts we use, and since on the entire exam they are given balanced equations, they should be made to demonstrate their prowess at it.

    Agreed. Why the whole exam used to expect balanced equations and then suddenly abandon that philosophy in question #4 never made any sense to me. I think that the new situation will be “better” – but we’ll see.

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