[justin2000]

I am making a 10,000 ppm stock of 2-CHLOROBIPHENYL
The 2-CHLOROBIPHENYL is a crystalline powder and is >99% pure. I am treating the powder as if it is 100% 2-CHLOROBIPHENYL

If I want a 10,000 ppm solution I was told to weigh out 0.5grams of the 2-CHLOROBIPHENYL powder into a volumetric flask and fill the flask to 50 ml with methanol. a weight/volume measurement. This doesn't seem to account for the density of methanol being less than water though.

My question is would it more accurate to weigh out 0.5g of the 2-CHLOROBIPHENYL into 49.95 grams of methanol? Total weight would be 50.0 grams, and the 2-CHLOROBIPHENYL would be at a concentration of 10,000 ppm.

[sjb]

As you have noted, the density of methanol is significantly different to 1 g cm^-3, so %w/v and %w/w will have different numerical values. What do you need the solution for? If, for instance, it's just making standards for further analysis both may be sensible.

[Vidya]

792 kg/m³ or  0.792g/mL is the density of methanol
so it means its weight is not equal to its volume
It will give you different vlaue for w/V% or w/w%