Day 44 and 45

I know it might be a cop-out to do a double post, but I’m trying to consolidate some time here. I have reasons, but I’m not going to discuss it here. Thanks for the understanding.

Physical Science: As we wrapped up discussing Physical and Chemical Changes, I introduced the students to the Law of Conservation of Mass and chemical reaction equations. This is really due to the fact that students take the WKCE exam, and every year they get a question about chemical equations and balancing them. As such, I decided that it had to be introduced somewhere. It was really the one question that most years students did not do well on.

It fits in, though not seamlessly like I wished it would, but since we talk about chemical changes, we can then talk about how scientists represent those changes. I describe the reaction equation as being the “language” or “sentences” of the chemist, mush like an essay might be used by a literature expert. It is our way of sharing the change that takes place.

So we go over the various parts of a reaction equation, and then talk about why in my example (the combustion of methane gas) there are two oxygen molecules on the reactant side and two water molecules on the product side. It introduces the idea of Conservation of Mass: the matter present before a change (physical or chemical) has to be present after the change. I do NOT let kids use the “cannot be created or destroyed” business. It’s not true when it comes to nuclear reactions, plus I don’t think it describes things in a meaningful manner. Hence, they don’t get to use it.

So that was Friday. Monday we spent the hour balancing the reactions I assigned on white boards. Students did okay with it. It’s an odd thing to do when we aren’t really diving deeply into the chemistry. It makes me think about how I used to teach Chemistry, back in the dark ages, before Modeling came along. By the end of first quarter we would have already done chemical reactions and some stoichiometry. In most text books all of this comes in pretty early, long before there is any heavy emphasis on particle behavior, interactions, etc. Personally, I don’t care for the text book model.

Chemistry: On Friday we went over the gas law problems. Everyone did a really nice job. In years past we have not developed the combined gas law, and rather have focused on the individual relationships. I think as long as there is a firm understanding of how each relationship (PVnT) affects the other, then the combined gas law is the way to go.

Monday, I assigned the Unit Review. I guess we’ll have to see how it goes tomorrow.

Physics of Light: We began talking about the start of the Converging Lens Lab proper. We set up the experiment, talked about the data to collect and the procedure. Some groups got into the data collection part, some groups didn’t get past writing their hypothesis.

All of the groups rationalized that the relationship between image and object distance should be inverse. Based upon all of the information gathered in the Pre-Lab, this was not surprising. However, there was a lot of discussion about how lenses with different focal lengths might affect the data. Most groups seemed to think one of two things: All of the lines will stack on top of each other, or they will be “parallel” to each other, or what ever the corresponding word would be for inverse curves.

On Monday data collection continued, with most groups getting into plotting the information.


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