Thread: equation
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Old July 6th, 2005, 18:49
charco charco is offline
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Your answer is clearly wrong!

Just think of how big 1cm3 is (1cm3 = 1 ml) ..... now consider how big 0.00977 mL

You would not be able to see this quantity of solution!

OK lets start from first principles and discount a few fallacies:

If the density is 1.3678 g/cm3 this means that every cm3 has a mass of 1.3678 g

Now the density of water = 1g per 1 cm3

therefore 1 cm3 of solution also contains 1 - 1.3678 g of solute = 0.3676g

If you require 25g then you require 25/0.3676 cm3 = 68cm3

But this wouldn't take into account any change in volume of the solvent!

Now a 35% solution means (usually) 35% weight/volume ratio.

In other words 100cm3 contains 35g of solute

You need 25g therefore you need 25/35 x 100cm3 =71.43cm3

But again this doesn't take into account change in volume of solvent on production of solution.

So?

If 35% w/v solution has a density of 1.3678g/cm3 then this means that in every 1 cm3, 35% of the mass (1.3678g) is due to the solute...

So in 1cm3 of solution there is 35/100 x 1.3678g of solute = 0.4787g

OK?

So if you want 25 g solute then you need 25/0.47873 cm3 solution = 52.22cm3

Capichi?