I have to prepare a 4000 ppm 100 ml solution from 99.8% of Methanol. Since density of methanol is 0.792. Do I have to multiply it to 10^6 to get the ppm of 99.8% methanol? I am confused about that.
4000 ppm (mg/L) is a mass concentration. Its also a fairly low one. just weight off 4 g of methanol and add a litre volumentric flask. Top up to 1 L. Alternatively, add 0.4g of methanol to a 100mL volumetric flask and top up to 100mL.
If you want to correct for the 0.2% of water already in the methanol you can weigh off 0.4g/0.98=0.408 g of methanol. Unfortunately, methanol is hightly hygroscopic at those purities and likely will draw more atmospheric water when not sealed. It is likely that the 99.8% is not longer correct.
If you want to use a volumetric measurement for the methanol, i dont advise it, just calculate the volume from 0.408/0.792. Keep in mind the temperature affects the density.
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