Parts per notation question

[mikool]

Hello,

If we used AAS and found the concentration of sodium in a 50mL solution (diluted apple juice, dw about the dilution factor) is 100ppm. Can you say the concentration is 100 milligrams / 1 Litre? I thought you couldn't say that because ppm is meant to be dimensionless (on wiki, i know not very reputable but w/e), and the only time you can mix ppm is if it is water or something with a density of 1g = 1mL?

So basically if ppm is dimensionless can 100ppm of solution equal to 100 milligram / 1 Litre if density does not equal to 1.

If yes, then do we assume the density is 1 if not given the mass of solution?

Thanks!

[Limista]

Density and concentration are two mutually exclusive concepts. We cannot assume anything about density from the concentration.

Someone please correct me if I'm wrong.

[lzxnl]

Actually, mikool is right here. If we assume that one litre of water is one kilogram, then mg/L becomes mg of solute/kg of solvent, which is ppm (mass/mass).

[Limista]

Actually, mikool is right here. If we assume that one litre of water is one kilogram, then mg/L becomes mg of solute/kg of solvent, which is ppm (mass/mass).

I see. Sorry about that mikool & hope I didn't confuse anyone.

[mikool]

I had a sac where we had 25mL apple solution that had a sodium ppm of 100.

Then to find the mass of sodium u had to do 100 milligram / Litre times 25mL.

Im not sure whether you can do that or not because we know nothing about the density of the apple solution??

[Alwin]

I had a sac where we had 25mL apple solution that had a sodium ppm of 100.

Then to find the mass of sodium u had to do 100 milligram / Litre times 25mL.

Im not sure whether you can do that or not because we know nothing about the density of the apple solution??

Okay, generally ppm and ppb are gram per million grams and gram per billion grams respectively. However, you will often see concentration notions such as (%w/v) which is percentage of mass of solute per volume of solvent. If you are given a density, eg for my last sac we were given density of ethanol = 0.785 g mL-1, you use the density to find the volume / mass required for the units of your concentration. However, as we generally use water as a solvent with density of 1 g/ml, we can safely say that:
ppm = grams per 1 million grams = grams per 1 million millilitres = milligrams per 1 litre

Only if you used a different solvent, say ethanol, then you cannot make the above statement. For ethanol you would go:
ppm = grams per 1 million grams = grams per 1.27 million millilitres = milligrams per 1.27 litres

For your question, I would actually say, "mass of sodium u had to do 100 milligram / 1000 mL times 25mL." Remember to keep your units consistent

I hope this makes sense to you, and good luck with your studies!