My sister rang this eveing wanting to know the answer to her daughter's science homework, "why does lemonade stay fizzy for longer in the fridge?" Now that's a good question and I was left wondering what the required answer is for Year 7 science. Unless education has change drastically,things like ideal gases laws, partial pressures and vapour pressures, to say nothing of potential for osmosis through vessel walls, solubility of gases in liquids, electron excitation etc will not have been the intended response (I'm only showing off a bit, most of things I can no longer remember anything about). Indeed, I wondered if the question should have continued '... after it has been opened' because I don't know if we have done the research to show that it does if it isn't (or which theories I'd need to apply). What container was it in - I mean, if in an open can or glass, it will still go flat pretty rapidly. And even, how does one define 'fizzy'?
I concluded the answer required was 'because it's colder.' The pressure x volume is lower (remember the old Pv=nRT ?) but whether this means the bubbles are less likely to collapse or less likely to escape from the fluid I don't have a clue, if I ever knew. It could be to do with electron excitation or evapoartion into the 'void' above the drink - or a whole host of other things I haven't a clue about. And I really can't see the mechanism as being what her teacher is expecting - though it would be fun to be able to tell her/him. Maybe someone out there knows the 'real' (degree level) answer and can tell me? Maybe someone, somewhere is doing a PhD in lemonade fizzics (sorry, couldn't resist)
But what all this did do was remind me of the difference between the 'right answer' and the 'appropriate answer' - and how they can be really rather different. I have many memories of A level Chemistry teachers alluding to the 'O level lie' we had to unlearn in order to learn what later turned out to be the 'A level lie.' Such a statement is a little hard, given the 'lies' were only ever incomplete or simplified answers, fit for our needs at the time. I think that there is a case to be made for 'appropriate' answers - and indeed, if we're honest that's all we ever get becuase all theories end up with limitations anyway.
Since my niece has ambitions in dramatic arts, I doubt that the mechanics of compressible fluids or solunilityof gases under different conditions are of very much interest to her. Knowing lemonade will stay fizzy in the fridge longer than out of it will be of greater use than the whys or wherefores.
Now, where's that paper on adiabatic expansion...