Stumbling on Unit Conversion 1

[caneng2002]

I want to check a coversion from ppm to ml/l.

Material O2 - Oxygen Density 1.429 kg/m3....1.429 mg/ml

Quantity 0.3 ppm O2 which is equal to 0.3 mg/kg

Math 0.3 mg/kg divided by 1.429 mg/ml = 0.2 ml/kg

Problem - reference I'm using shows the coversion to be 0.2 ml/l How is ml/kg converted to ml/l. If this was water i would just say 1l = 1kg but this is a gas.

Help...Thanks

 

[caneng2002]

Actually I think I can answer my own question.

For non-liquid solutions ppm to mg/l is calculated using

mg/l = ppm * Mol Wght / 24.4

Then using density of gas divide mg/l by mg/ml answer is in ml/l units

so for oxygen 0.3 ppm * 32/24.4 = 0.393 mg/l
divide now by density 0.393 mg/l / 1.429 mg/ml = 0.275 ml/l
which is pretty close to 0.2 ml/l.

Sound correct?

 

[Jobst]

Watch out for units -- molecular weight is g/mol, standard volume is l/mol so in the first line of your second calculation the units of 32/24.4 is in g/l.

additionally, ppm in a liquid system is often expressed as weight/weight, while for air and gas it is often mol/mol (which is identical to volume/volume for most gases at low pressures, but can be substantially different to weight/weight).

 

[25362]

See thread127-48308 and thread127-97413. Besides, what are T, P conditions and the nature of the dissolving gas ?

 

[caneng2002]

Thanks for the pointers.