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Help appreciated for an interview lesson on moles

Discussion in 'Science' started by Rhysboy, Dec 18, 2011.

  1. Rhysboy

    Rhysboy New commenter

    Does anyone have any good ideas/activities for introducing the concept of moles, relative atomic mass, relative molecular mass and mass to mole calculations?
    Fairly dry topic I know but I would appreciate any ideas.
  2. WHENEVER someone comes on asking for ideas, I ALWAYS ask "what are YOUR thoughts?".
    It is, when all is said and done, YOU who is applying for the job. To appoint you totally on someone else's work would be unfair. I accept it would be you delivering the lesson, but I would like to think that I was appointing someone with their own ability in this field.
    Sadly, you have chosen a bad time to post, as many folk will be off enjoying a break now and will leave thoughts of school until the New Year. If you don't get any other help, I suggest you post your ideas early in January.
  3. Rhysboy

    Rhysboy New commenter

    <font size="2">What a pompous
    fart you are.</font>
    <font size="2">I suppose that
    every lesson you have ever taught has been all your own ideas? You've never
    asked a colleague for ideas, or seen an idea in a textbook or scheme of work
    and thought you'd give it a try? I thought not. </font>
    <font size="2">If you don't have
    anything useful to say, then it's best to say nothing. This is some advice that
    you'd do well to take on board. </font>

  4. Cornholio

    Cornholio New commenter

    Try this for starters, some nice info and you could play it or lift ideas from it:
    Good luck!
  5. Clearly your 1-5y experience, some of it in Japanese society where respect is highly prized, has allowed you not to mince your words. Sadly, you missed the opportunity to add "old".
    And apparently, you have also learnt to think - wow! Yes, I've bought textbooks to allow me to expand on schemes of work and I've asked for help from colleagues BUT I've made an effort FIRST. Only spongers expect other people to do all the work for them.
    Try reading my useful advice - "give us your thoughts and listen to the feedback". Then, make your choices and take pride in what you do. I know that is harder than relying on generous teachers who have done just this for decades, but I would like to think it is what you expect your pupils to do - it's called independence and is much more educational than spoon-feeding.
    Have a Merry Xmas.
  6. I have recently joined the TES forum and am amazed when I see comments such as these. We are in a difficult profession where everyone is basically doing the same thing but in different ways. Why not share ideas?
    Also, it is now increasingly common for teachers at interview to be asked to teach outside their specialism. Surely, seeking help shows more commitment than someone who sits back and expects everything to fall in to place on its own. An eagerness to succeed does not imply laziness!

  7. I agree entirely.
    But allow me to quote the original poster "Does anyone have any good ideas/activities for introducing the concept of moles, relative atomic mass, relative molecular mass and mass to mole calculations?"
    I do not call that sharing. And it's not as if this person is looking to educate pupils - "he" is looking to advance "his" career.
    If "he" had written (deleting alternatives): "I have obtained an interview in a highly selective private school / inner city comprehensive / mission school in the depths of the Amazon Jungle. I have to present a 10-minute starter slot / 1-hour introductory lesson / half-day workshop to a group of aspiring Oxbridge entrants / mixed ability Y11 group / Y9 low ability boys with ADHD. The topic is one about which I know very little / have taught a couple of times / formed part of my PhD thesis and I've already searched on TES Resources, which threw up 384 matches and 21 specific items. I've looked through all of them and would like to use numbers 3, 7, 11 but would really appreciate any additional tips. I've also found a wonderful video on totallycopyrightfilmclips.com and wonder if anyone knows an alternative.
    Thanks for taking the time out of your Xmas holidays to read this and I would appreciate any comments. I'll let you know what I did and how I got on."
    I would then hope that lots of positive responses might flow in, although holidays are not a good times to ask for help. Sadly, rhysboy does not seem to think "he" should do this but should sit back and let others find the resources and write to "him" about them. Even worse, "he" is not alone in adopting this technique and I am amazed that people support this attitude.
    If I wanted to appoint a teacher, I would not give much credence to someone who said "I plan my lessons by writing a note on TES website and waiting for others to do it." The additional statement "often I do it on the night before the lesson" would represent a true response from some teachers. I happen to believe that children deserve better than this (although I'll admit even that is better than no science teacher at all [​IMG] ).
  8. Mangleworzle

    Mangleworzle Star commenter

    Since when? It's always been like this, before the internet, the first port of call was ourselves and not to get someone else to do it for you. It is a certain type of teacher who uses others as their first port of call. It's the equivalent of some kid trying to get teacher to do their coursework for them because they want to do well but can't be ***** to make the effort.
  9. Hello,
    Something that has always interested my students is to take in 1 mole of sugar or salt or water in a pollytop or pill vial. It gives visual reference for a somewhat nebulous idea. If they have access to balances you could get them to calculate the mass of 1 mole of various household stuff (bicarb etc) and weigh it out.
  10. My experience has been this: what confuses students are three very basic things, namely, (1) what kind of thing a "mole" is, (2) how large a mole is and, intimately related to this, how small atoms are, and (3) how we use the concept to do chemistry.

    They also need to be fairly adept at making simple calculations like "If I have 50 pencils whose mass is 15 grams each, how many grams will 10,000 pencils have?" And the inverse problem: "If I have 35 kg of ball bearings, each one of which has a mass of 14 grams, how many ball bearings do I have?" Once they can easily do these, you can add one more twist: if ball bearings are packed in cartons -- say, 12 to a carton -- how many 12-to-a-carton cartons do I have, if I have 35 kg of ball bearings. [Ball bearing = proton/neutron; 12-to-a-carton package = carbon atom]

    And they need to know that a proton and a neutron have approximately the same mass, and that each element (each isotope of an element, strictly speaking) has a distinct, characteristic number of neutrons and protons, which we call its "atomic mass" but which is better thought of as its neutron-and-proton count.

    (1) They don't quite get that "mole" is just a name for a counting number. Just as "pair" is another name for "two", and "dozen" is another name for 12, so "mole" is another name for 602 followed by 21 more zeroes. That's the first thing to hammer home. We could avoid using the word "mole" altogether: we could just say "six hundred and two umpty jillion" (or whatever) but it's easier to say "mole". We COULD, but don't have occasion to, use "mole" to count anything. Except that there are very few things of which there are so many of them, that we need a number-word like mole. Even the number of stars in the universe is probably a bit less than a mole. (Assuming a hundred billion galaxies each with a hundred billion stars.)

    (2) The second idea is that this is a REALLY big number. Most students don't really have an intuitive grasp of the powers of ten idea, so scientific notation, although convenient, may obscure the great size of this number. To give them some idea of the relative size of this number, you might do something like saying, "consider all the people on the earth right now ... about six billion. If I had a mole of pounds, I could give each one of them .... ten, times, ten, times ten, times ten, times ten .... pounds" (and keep going until you've multiplied by fourteen "times tens".) In other words, with a mole of pounds, everyone on earth could be a trillionaire, a hundred times over.

    Of course, such a big number is only necessary, because atoms and molecultes are so very very very very very small .... that to count any useful amount of them, we need a really really really big number. (You should already have gotten over just how small atoms are -- the example I use is that if a frozen pea were to be expanded so that it was so large, that we could see its atoms, it would have to be the size of the earth, and the atoms would be about the size of cricket balls. [An opportunity for pedants here]. If atoms were the size of oranges, we could use "dozens" instead of moles.

    This number is arbitrary, in the sense that the choice of our unit of mass, the gram, to which the mole is tied, is arbitrary. Which brings us to the third, key, idea:

    A mole of protons (and/or neutrons) has a mass of one gram. (How we know this is another question, and maybe worth exploring with the more able students.) (When you're introducing an arbitrary fact, one that cannot be deduced from previous knowledge, you should always point it out. Otherwise students will tend to think that all knowledge is arbitrary.)

    (3) This is the critical point. Knowing that a mole -- a certain number -- of protons/neutrons (whose mass is very nearly the same), has a certain mass, allows us to move from mass, to count, and back again. If I know an egg masses at fifty grams, I can calculate the mass of 10,000 eggs. Or, if I know I have 20 kilograms of eggs, I can work out just how many I have.

    And since I know, or can find out from the Periodic Table, how many neutrons/protons (you need to point out that their mass is almost the same), an atom of particular element has, then I can work out how many moles of those atoms there are in a certain mass of those atoms, and vice versa. And same goes for a molecule, of course.

    And I need to be able to go from mass to count and back again, because my understanding of chemical reactions is in terms of count: one atom of carbon unites with two of oxygen to make one molecule of carbon dioxide, and thus one mole of carbon will unite with two moles of oxygen atoms, etc. But my practical manipulation of carbon is in terms of its mass: I cannot, as a practical matter, count out a mole of carbon. But I can easily use the scales to get 12 grams of it. (Although it would be theoretically possible to cool oxygen down and then measure 32 grams of it, I also know -- we needn't explain how -- that one mole of atoms as a gas takes up a certain volume ((at a given temperature and pressure)), so I can measure my gases by volume instead of by mass. Better to postpone this idea until your students are comfortable with mass-to-moles and back. Molar volumes and molar concentrations can come later, and will be easy, once they are fluent in the mass-quantity conversions).

    Another small wrinkle: note how one and one can make one, not two. One mole of oxygen atoms can join to another mole of oxygen atoms, to give one mole of oxygen molecules, just as one dozen pieces of chocolate can join with one dozen wrappers to give one dozen wrapped pieces of chocolate.

    If all of these ideas are introduced all at once, they will utterly mystify your students. You've got to introduce them over a few weeks, one at a time, with calculation practice repeated several times. First, the basic idea of a mole as a number. Then, the link between that number, and mass, for nucleons. Then simple calculations going from a certain number of moles of a given atom or molecule, to its equivalent mass, and back again. And finally, using this to do stoichiometry problems.
  11. Thank goodness somebody can see my point of view.
    I wonder what sort of teacher just responds with masses of advice, even when it doesn't address the question? [​IMG]

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