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Joined: Apr 2009
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Because no matter what I search for, I can't find the old one. If anyone can find it and merge this with it, please do!
DD7 brought home a science worksheet from 2nd grade. Some of the questions have me stumped as to what they really want.
"Tell whether water is a liquid or a solid in each picture." And the pictures are a house with snow on it, a fish bowl, and a pan of water on the stove with steam coming out of it. Now, I would expect the steam one to be gas, as did DD, but that's not a choice -- it does have water still in the pan, so we went with liquid.
"Tell what happens when heat is taken away from water." Umm, it gets cold? How much heat, exactly? Might or might not be enough to make it freeze. "Tell what happens when heat is added to liquid water." Again, how much heat? It gets hot, it boils, it evaporates...depends.
"What kind of change is it when matter can be changed back to the way it was?" This would be fine, but it's not until the next page when they explain reversible and irreversible. This is a page about liquid and solid.
And the next page, reversible and irreversible, is a real conundrum.
"Decide if the change is reversible or irreversible." First one is easy, an egg and a fried (or at least dumped out) egg. Then comes a bowl of ice cream, melting. Hmm. Well, ice cream can be re-frozen, but it doesn't come out the same. Hard to say what they're going for. Then comes a picture of what DD says is popcorn but I thought was drops of water and clouds. One is reversible, the other isn't. Then a picture of a bunch of screws and washers. They can be melted, so it must be reversible. And the last one is what appears to be a rusty nail. Rust can be removed, but it's not exactly reversible. She didn't even know what "that stuff" was on the nail.
The last page has three words, reversible, irreversible, and mixture, and three pictures to label with them. A pond that may be frozen because it has trees with snow around it, a pizza with a slice missing, and a bowl of fruit. WTH? Is a pizza irreversible, because you can't unmake it, or a mixture? Is a bowl of fruit a mixture, or irreversible because you can't put it back on the trees? Who knows?
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Joined: Dec 2012
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Now I'm confused. I guess it is just change of state they are looking at and just the most obvious answers?
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See, I think that's fantastic homework, for exactly the same reasons you thought it was bad. Sparks interesting and pertinent discussion about exactly what reversible ought to mean.
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If you really want to geek out the teacher then:- Rust reversal
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That's not reversal, though, that's removal. The oxidized iron doesn't become un-oxidized, it just falls off.
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See, I think that's fantastic homework, for exactly the same reasons you thought it was bad. Sparks interesting and pertinent discussion about exactly what reversible ought to mean. For middle school or high school science, yeah-- awesome and thought-provoking. I used to ask some of this same stuff of college freshman, fwiw. They found it somewhat challenging to consider, for the reasons that Nautigal notes.
Schrödinger's cat walks into a bar. And doesn't.
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That's not reversal, though, that's removal. The oxidized iron doesn't become un-oxidized, it just falls off. I stand corrected, it's the black rust that will rebond not the red although phosphoric acid will turn the res into black after which the above would then work. Yes?
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While transition metal oxidation is generally "reversible" in the technical, electrochemical sense, in practice as a materials science problem with real world applications in situ, the answer is "not so much." The problem is that the structural shifts that occur during oxidation don't reverse simply by reversing the chemical change. In solution, this isn't so-- it's a solid state issue. This is the reason why electroplating isn't a DIY project from solution, in most instances. Oxides generally aren't soluble enough in solution to allow for reversibility and 'replating' onto a surface once they fall off in a "spongy" or "columnar" form. I know, this is probably way more than anyone wanted to know. Occupational hazard.  This touches upon my DH's research expertise and the overlap with my own elecrochem background, so it's something he and I have discussed a lot over the past 25y.
Last edited by HowlerKarma; 03/07/14 10:23 AM.
Schrödinger's cat walks into a bar. And doesn't.
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No - thanks for the info - I am always happy to learn even when I learn that I was wrong LOL
Last edited by madeinuk; 03/07/14 10:58 AM.
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Is this the thread you're looking for?
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