This one’s a guest-post from Fisherman. Fishy’s a keen golfer, fresh-water fisher, quiz enthusiast and, most importantly for us here, a chemistry teacher.
I’ve been after him for a while now to do a piece on kitchen chemistry; something that parents could do with their kids, maybe, or those of us who never grew out of that childhood fascination with the world that makes us gasp with delight when, with some ordinary, everyday bits & bobs, we realise we can discover some quite astounding things.
Anyway, enough from me, already! Here’s Fishy:
The experiment is basically very simple. A drop of oil is allowed to fall onto the surface of a bowl of clean water and spread out until it is only one atom thick. We can estimate the volume of the oil drop and measure the area of the drop when it has spread out. A bit of maths will let us calculate the depth of the spread out oil drop which will be the size of one of its molecules.
Volume of drop = area of spread × height of molecule.
Find a bottle of Olive oil. We need one small drop of this. The best way to get one small drop is possibly to dip a needle into the oil and let it drain until about one drop remains on the end, ready for our experiment.
If the drop of oil is too large then it will need a big bowl to spread out fully. A 1mm diameter drop should spread out to a circle of about 250mm.
The diameter of the drop allows us to calculate its volume.
Volume of the drop = 4⁄3 π × r3
If the drop is about 1mm across the volume works out at roughly 0.5mm3
We now fill a bowl with clean water and sprinkle some fine dust on the surface. Pepper works well! When you place the drop onto the water surface it spreads out and the pepper shows the extent of the spreading. It is worth leaving it for a few minutes to give the oil chance to spread to its full extent. The area of the drop needs to be estimated.
Let us Assume that the oil spreads into a nice circle of about 250mm diameter.
The area of the circle can be calculated using the formula π × r2.
The area for our drop is roughly 50,000 mm2.
The height of our Olive oil molecule is therefore
0.5 ÷ 50,000 = 1⁄100,000 mm ( 1 × 10-5)
this is 1⁄10,000,000 m
Now a molecule of Olive oil is about 12 carbon atoms deep…
so the size of a carbon atom is about 1⁄100,000,000 or 1 × 10-9 m
—Fisherman
Fishy’s quite obviously correct in stating the result in metres—the SI unit of distance—but if, like me, you’d prefer to stay in the units we started with, millimetres, that last calculation goes:
… the size of a carbon atom is about 1⁄100,000, or 1 × 10-6 mm
In email conversation, Fishy also mentioned the problem of estimating the size of the oil-drop. Obviously, the bigger the drop, the more accurate you can be with that, but also the bigger the surface-area of the water will have to be.
Also, and I quote Fishy’s own words here, “you might want to add a health and safety warning that using yer mother’s olive oil and pepper without asking may result in a smack round the head.”
—Daz
If you liked this, you may also like How To Measure The Speed Of Light Using Your Microwave Oven
Damn, that’s cool. Like the microwave trick, I’d have never imagined that this would be this easy. Hmm. What else could we do?
Well, I seem to remember summat about using red-cabbage juice to test PH, like litmus. Presumably it’s not as sensitive/accurate, ’cause cabbage is a helluva lot easier to grow than lichen, and yet litmus is still used. Fishy’ll know, I assume.
*googles; returns to writing comment*
Yep, here we go.
Oh an’ I just remembered AnnMarie Thomas: Hands-on science with squishy circuits.
red cabbage is a suprisingly good indicator. It is far far better than litmus and has a better colour change. The best way to make it is to chop some red cabbage then place it in the bottom of a small glass. Add a bit of alcohol ( colourless meths or vodka) and place in a bowl of hot water for 30 mins. Pour the coloured liquid slowly onto blotting paper and let it dry!
If it’s better than litmus, and given that a lichen must be very hard to farm (slow growing ‘n’ all that), howcome we still use litmus? Not that I’m doubting you! Just curious.
Incidentally, if yer heading off to TED to watch that squishy circuits thing, make sure to check this chap out while yer there. He’s amazing!
Litmus is just the first indicator…. it made it to the history books and established its place in crosswords and quizzes….coff….red cabbage is much prettier but never made it commercially as everyone uses a mixture of indicators called ‘Universal’ or pH indicator which has a wide range of colours and shows a wide range of acidity values even though it is quite expensive!
now, if you have access to an old test tube…
and an empty plastic lemonade bottle…..
there’s Cartesian Divers to play with…..
You don’t even need a test tube. A pen cap’ll do.For best results, use a cap from a cheap biro; the ones where the pocket-clip is a spur that sticks down from one side of the cap. Use a small piece of plasticine to seal the air-hole at the tip, and attach a larger bit to the end of the pocket-clip to give it some ballast.
that’s the one!!!
wd Daz…..
mind you….
if you can find two pen tops.. of different sizes….
it gets even more interseting!!!
Go on, I’ll bite. Explain please…