wraithgirl ([info]wraithgirl) wrote,
@ 2008-08-13 18:15:00
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Calculations!
I have to convert 250 000 tonnes into litres. Any ideas how to do this?

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[info]davesbrain
2008-08-14 02:17 am UTC (link)
Apples and oranges. Can't be done. Litres is a measure of volume. Tonnes is a measure of weight.

It could only be done if you were given a specifc substance (air? water? rock?) because you need to determine the density.

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[info]wraithgirl
2008-08-14 02:25 am UTC (link)
It's seawater, actually. But I think it's become much too complex for grade 8.

I was attempting to design an activity around a feature that is already set in place (and can't be changed). The feature states that "if you wanted a gram of gold [from the ocean], you would first have to make 250 000 tonnes of ocean water evaporate."

I was able to find cost figures for desalination (via distillation) at $252 per L but I was stuck with that figure in tonnes, so I was trying to convert it. Then it got ugly.

To boot, I'm not convince that the 250 thousand tonnes is actually correct. Brief googling has turned up figures much, much higher than that.

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[info]davesbrain
2008-08-14 02:46 am UTC (link)
Oh. Well, freshwater is exactly 1kg per litre; 1000 litres is one tonne. Very nice round numbers.

Seawater is a mere 3% denser, at 1.03kg/L. You could make a note about ignoring that 3%.

$252/L works out nicely to $252,000 per tonne.

Wow, so it would cost $252,000x250,000T = $63,000,000,000.


(Of course, distillation STILL doesn't give you gold, it merely gives you everything in seawater that's NOT water, You'd be left with 99% salt and still have to extract the gold...)

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[info]davesbrain
2008-08-14 02:48 am UTC (link)
"...for desalination (via distillation) at $252 per L..."

My numeracy alarm has gone off. There's something wrong with this number. It cann't possisbly cost $252 to distill a single litre of water.

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