Students from high school might understand that vinegar for example is a weak acid compared to hydrochloric acid, but they never knew why. And you could then show them that with equilibrium, this is why. And all of a sudden they’re, 'oh, I’ve always known that I shouldn’t spill HCL on my hand, but I can spill vinegar on my hand and put it on my fish and chips'... Those sorts of moments can really... the students go ‘oh wow.’
Use several real life examples with different ways of causing the equilibrium to shift. Swimming pool chemistry:
HOCl can enter the cells of undesirable organisms to kill them, but OCl- can’t, hence if the equilibrium is too far to the right it won’t act effectively. If you add acid (say HCl) the position of the equilibrium shifts to the left, producing more OCl-. That’s partly why the pH of the pool is important.
Use everyday examples. A great question to have at the end of your lecture would be ‘What is reduced when my bike rusts?’ They might understand that their bike rusts, but what is reduced? Oxygen and water are reduced. But we don’t see the reduction, we just see the iron changing. You have done your job well if someone asks the question ‘What is reduced when my bike is oxidised?’
Put zinc metal in copper sulphate solution and record it with the visualiser. Have it running as you talk about the push and pull of electrons. Then bring it up and say, ‘look what’s happened here, the zinc has rusted’. Students make more of a link when they see things being visualised. The oxidation of metal has a very visual impact on them. But then, they might forget about the reduction side, so you need to remind them of it.
If you put copper metal in a silver nitrate solution, the solution becomes blue and you get silver metal. Ag+ is becoming Ag and Cu is becoming Cu++. The students see both oxidation and reduction happening - and happening at the same time. If you do it close to Christmas you can use the copper filament to make a Christmas tree, and then you get a nice silver on the Christmas tree. They know that it was a colourless ion solution, but then they can see silver on the Christmas tree. So they can easily see the reduction.
Re-teach electronegativity quickly because you don't necessarily trust the person who's taught before you. Make sure that it's reiterated, and then follow through to bond polarity and partial charges. Include all of that information first before going on to do reaction mechanisms. So the first thing to do is draw in partial charges to identify the electrophile and the nucleophile before going on to the next step. It's about doing examples all the way from first principles to build up those concepts.
Do many examples, on the projector or board, from first principles. Start with partial charges and identification of the nucleophile and electrophile, then draw in arrows.
In some practical demonstrations it is very simple to see which reagent is limiting, for example if one of the reactants is liquid and you add just a tiny little bit of salt to it. Just from looking at it, which one do you think will be the limiting reagent here? We have 20ml of A, and we’re going to add half a gram of B. We know though that the number of moles is the important thing, but sometimes it works just to illustrate the concept.
