Thursday, September 15

Chemical Chronicles: Answers

Jeremy has completely answered the questions to the original quiz, which saves me the trouble of going through the exercise myself. Now I'll just go down the list and fill in the few gaps he left while explaining the rationale behind each question. Where my students got the answer wrong, I'll say so; otherwise, you can assume they answered the same way as Jeremy. To be honest, I was not expecting them to do nearly as well as they did, which elates me because it makes my job a lot easier.

  1. I fully expected my two students to be able to name ten elements. The question was, which ones would they think of. It turns out they thought of the common metals fairly quickly, (copper, silver, gold, aluminum, etc.) but they struggled after number 7 or 8. After a few minutes, they remembered gases like hydrogen and oxygen. The song that Jeremy quotes is a brilliant, no doubt; I was already planning to play it for them once we cover the periodic table.
  2. This was just to see if they had any familiarity with SI prefixes. Strangely, they didn't know where "mega" fit on the scale. Neither do most non-scientifically-inclined adults I have polled, actually, which is distressing; they tend to think that a megameter is smaller than a kilometer. Weird.
  3. This was a sneaky way of finding out if they've ever heard of a neutron. Most people say, "Proton, electron... uh... " and then they proudly think of neutron after a long pause. If my students said pi-mesons or gluons or some such, then I'd know they were hobby science nerds.
  4. Most people know about sodium chloride, or at least slap their foreheads when told the answer (their own forehead, not someone else's). My goal was to reassure my students that the intimidating concepts of chemical nomenclature were not entirely foreign to them.
  5. The ion is a fairly critical concept that, if my students didn't know about entering grade 10, would make me very sad. Jeremy's answer, "a charged particle," is bang-on.
  6. This question was a sneaky way to see if my students had ever heard of the concept of specific heat capacity, one of the few things I actually remember doing in Grade 9. Most people can get this question by intuition, but the next one throws them for a loop.
  7. The few adults that I've informally quizzed have totally guessed at this. My students did the same. The correct temperature would be "close to that of water."
  8. Carbon dioxide, strangely enough, is the first thing that most people say - probably because they read about it in coverage of greenhouse gases and global warming. My students knew the correct composition of air; however, they didn't know that the third ingredient (forming almost a whole percent) is argon.
  9. There are tonnes of answers to this question: soft drinks, exhalation, combustion reactions, car exhaust. Strangely, this almost stumped my class until they said... car exhaust. Again, I'm guessing, probably because they've learned about the greenhouse effect before. After a while they said exhalation, which is a good thing because I expected them to know that from their Grade 9 biology class.
  10. I wasn't expecting my students to know about the spectrum of electromagnetic radiation, but after a few minutes of brain-wracking, they remembered that the difference between the colours is wavelength. The adults I've polled (present nerds excepted) have no idea.
  11. The crystal lattice is a very important concept in semiconductor physics, but my students didn't know about it. They do now!
  12. The ol' magic static clinging balloon trick! Most children know the answer to this question; I asked it to get them thinking about electrostatic forces, which I want them to do before we start learning about the atom.
  13. One guy I polled said "the sun is a mass... of incandescent gas," which proved that he heard the They Might be Giants song "Why Does the Sun Shine." I asked this because I wanted to sneakily hint at (a) the distribution of elements in the whole universe and (b) the stellar origin of the heavier elements.
  14. I remember spending a whole lesson or two in my high school chemistry course about the states of matter. Most people know what they are anyway. If I can build off my students' inherent and intuitive knowledge of these concepts, I don't have to waste anybody's time.
  15. Bubbly ice: this is the only really tough question. I asked it to see if they knew that liquids (like water) could dissolve gases (like air) as easily as they could dissolve solids, like salt or sugar. Anyway, here's the full answer: the ice cubes in your fridge freeze from the top down. The first layer of ice seals off the water from the atmosphere. Then, as that layer thickens, dissolved gases evolve from the water little by little, forming a cloudy haze of small bubbles in your ice cubes. Restaurants have special machines that freeze the water from the inside out; basically, they consist very cold pipes immersed in water that freeze the water along their surface. This is also why your glassy-clear restaurant ice cubes often have that hole in the middle. Incidentally, you could make clear ice cubes in your refrigerator by boiling or distilling your tap water first. This would remove any dissolved gas.
  16. What is fire? Ah, the classic age-old question. All children ask this one, but how many people really know the answer? Well, Jeremy's response, "a too rapid exothermic reaction," is pretty good, but it's not the whole story. I'd put it here, but why not get the Straight Dope.
  17. This question had two goals. One was to see if my students heard of Pascal's Law. But even if they had not, the correct answer would have been, "let's try it out." A good scientific spirit involves always being ready and willing to experiment. This is a simple but intuitively perplexing experiment to perform for your friends and family. Try it!
  18. We are going to cover the definition of an alloy in the coming months; we might even get to coat a penny with brass, which is a very fun lab I remember performing in high school. I asked this question just to see if they were familiar with the concept. Sure enough, they could think of brass and steel... and whatever that nickel-zinc alloy that their American "nickels" are made of these days.
  19. "Why is the sky blue" is one of those "what is fire" questions. Everyone asks it and no one knows it. My students sort of did, but their answers were a little sketchy if essentially correct.
  20. Chemical reactions: strangely, this stumped my students, despite their having been asked "what is fire" only a few questions earlier. Upon prompting, they remembered combustion, respiration, digestion - all that good stuff, although I have to say that Jeremy's example of muscle contraction is pretty awesome. Here's another one: thinking! (I'm pretty sure a firing neuron involves some chemical change in the exchange of sodium and potassium. Am I right?)
  21. This one is a little tricky because while my students know the basic physical units for length, Mass, and Time, they had never seen the concept of "derived units." Hence their answer for speed was "kilometers per hour" and for pressure it was the Imperial "pounds per square inch." Most adults have no clue on these either, completely confusing power and energy, voltage and current, force and pressure, etc. It's not their fault, but it depresses me that the knowledge isn't as common as it should be.
  22. My students got this correctly, actually, though they probably guessed luckily. It turns out that salt melts before gold, which surprises a lot of scientists (who are probably thinking, hey, isn't that ionic bond supposed to be strong?) Sure enough, its melting point is still pretty high, just not that high.
  23. The mechanism behind the way a hot air balloon works isn't too complicated. I mean, my students could probably explain why air bubbles rise in water - it's the same principle, which Jeremy well and succintly describes. But they got it wrong, thinking that either it was some kind of action-reaction effect of hot air rushing out of the balloon (which would fry the occupants of the basket, but forget that) or something related to "thermals" rising inside the balloon "pushing" it up the way an eagle soars. It was interesting to see their misconceptions.
  24. A simple unit conversion problem. Everyone uses pounds (of gravitational force at the Earth's surface) for their body weight, and by Grade 10 I had hoped that they knew the conversion factor... but they didn't.
  25. Lemon juice, vinegar, the inside of a battery, ... stomach acids, etc., are all good answers to this question. They slapped their foreheards when I told them.
  26. How many molecules in a raindrop? It was interesting to see their guesses. One student said three million. The other student said 10,987,6534,321 molecules, just to be cute. Interestingly, he was stilloff by about eleven orders of magnitude. If a raindrop is on the order of 1 mL, which is about 1 mg of water, and the molar mass of water is 18 grams, then the real answer is closer to 30,000,000,000,000,000,000,000 molecules. The reason I put this question on the quiz is because a local three-year old came up to me one day and asked it, out of the blue. I was very happy to be able to answer him.
  27. This is a personal question that surreptiously, by covert power of suggestion, was meant to convince my students that science is interesting. Their answers? The human body, said one. Dissection, said the other.


JeremyHussell said...

#1: Check out this Flash animation of The Elements.

#13: Forget They Might Be Giants, go download the Sun Song by the Chromatics.

#14: The whole concept of states of matter actually gets pretty interesting when you dig into it. Fraxas suggested I should add Bose-Einstein condensates to the list, but if you do that you have to include all the other odd states of matter.

#20: Yup, firing a neuron does involve sodium and potassium. But like the other biological examples, there's a whole lot more going on. In particular, to bridge the gap between two neurons a completely different mechanism is used.

Anonymous said...

Good quiz, Pharao.
I think I got almost all of the answers right.

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