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Molarity of a solution!?

Hello, I know that a molarity of a solution is moles of solute / 1dm-3

so the units for molarity would be moles / dm-3

but i heard somewhere in the forum that you can have g/ dm-3 how is that possible? It wouldnt be Molarity then it would be something different?

Thanks for your time

From John Wood
Reply 1
Avatar for oxymoron
oxymoron
7
Neo1
Hello, I know that a molarity of a solution is moles of solute / 1dm-3

so the units for molarity would be moles / dm-3

but i heard somewhere in the forum that you can have g/ dm-3 how is that possible? It wouldnt be Molarity then it would be something different?

Thanks for your time

From John Wood


g/dm3 is just another unit of concentration. It is based on the mass you dissolve rather than the number of moles (ie number of atoms) you dissolve. I wouldn't call in Molarity though as molarity implies concentration in molar units I think.
Having said that, they are both just ways of describing concentration.
Reply 2
Avatar for Neo1
Neo1
OP
4
I mean it shouldnt really be called Molarity It's grams / dm-3 while the other one is moles / dm-3. In my notes my teacher gave me moles of solute / 1dm-3, is this ok for GCSE triple science exam i would have to use this one not the other right?

Thanks
Neo1
I mean it shouldnt really be called Molarity It's grams / dm-3 while the other one is moles / dm-3. In my notes my teacher gave me moles of solute / 1dm-3, is this ok for GCSE triple science exam i would have to use this one not the other right?

Thanks


For GCSE you'll need to know mol dm^-3

BTW, the symbol is either mol dm^-3 or mol/dm^3 because remember dm^-3 means 1/dm^3 if you remember the rules of indices in maths.

If you get something in g/dm^3 you'll also be given the formula of the compound or its Mr... use its Mr to work out the number of moles in that many grammes which is the concentration in mol/dm^3
Reply 4
Avatar for corkskrew
corkskrew
2
Not really helpful but my teacher calls this the "grammity phenomenon"
Oh how bored I am.
Reply 5
Avatar for Borek
Borek
4
For different concentration definitions check

http://en.wikipedia.org/wiki/Concentration

Best,
Borek
--
God, i just spent the last 4 hours revising moles in concentrations/volumes/ everything else for A-level. Finally got it under wraps, although a year and a half late i think!!

Good luck on any exams
Reply 7
Avatar for Neo1
Neo1
OP
4
LOL ok so I'll use mol/ dm^3 then...

Thanks

From John Wood

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