Is it possible to convert mol/kg to mol/l?

Hunders · 16 Dec 2014 at 09:31

Hi guys. Having a discussions with a mate and need some clarification.

Is it possible to convert the concentration of a given solute in seawater from mol/kg to mol/l? I'm saying no you cannot unless you have the exact weight of the seawater sample (as it will vary depending on several factors).

LOAM · 16 Dec 2014 at 09:39

You would need to know the density of the liquid in question, in relation to the density of water (1) to convert it iirc.

Rich_L · 16 Dec 2014 at 09:42

I would probably just grab the range of seawater densities from Google (1020 to 1029 kg/m3), take the mid-point and go from there.

Hunders · 16 Dec 2014 at 09:42

Yes, that's what I thought. He was saying all you need to know is the density at standard pressure and temperature but I was saying that the chemical composition of seawater may differ from one sample to the next, therefore changing it's density.

div0 · 16 Dec 2014 at 10:54

So your question is effectively - does all seawater always have the same density at stp?

Elixir · 16 Dec 2014 at 11:00

How can you work out mol/kg without having the mass of your seawater sample in the first place? Very odd sampling technique if you're not using a fixed volume or at least recording both volume and mass of the sample.

Muz333 · 16 Dec 2014 at 11:10

Elixir said:
How can you work out mol/kg without having the mass of your seawater sample in the first place? Very odd sampling technique if you're not using a fixed volume or at least recording both volume and mass of the sample.

Was going to say the same, although I'm a biologist rather than a chemist and haven't even heard of mol/kg before.

Hunders · 16 Dec 2014 at 11:54

We haven't sampled anything. Some literature values state their concentrations in mol/kg and I said that it wouldn't be possible to convert it to mol/l to compare to other values (which are mol/l) without knowing the mass of the sample.

Elixir · 16 Dec 2014 at 12:04

Hunders said:
We haven't sampled anything. Some literature values state their concentrations in mol/kg and I said that it wouldn't be possible to convert it to mol/l to compare to other values (which are mol/l) without knowing the mass of the sample.

In that case you'd need to know the density of the solvent (not the solution which is an important distinction) to convert from molality to molar conc.