I'm solving for the mass of PEG for my 500ml solution, however I don't know what density should I use to convert 50g PEG/kg H2O? Should it be of the H2O or of PEG? Thank you very much! This is my solution:
Concentration: 50g PEG/kg H2O
Vol= 500 ml or 0.5L
?g PEG= 50g PEG/kg H2O x 1kg H2O/1000g x 500 ml x density
The density you use should be that of the SOLUTION. Do you want to make a solution that is 50 g PEG/1000 g H2O?
Then you take 25 g PEG and dissolve it in 0.5L H2O (not solution) and that will be 50 g PEG/kg H2O won't it and you don't need density for that. I don't know what PEG is; on Google it came up with polyethylene glycol and that listed a density.
Thank you very much. Making the solution 50 g PEG/1000 g H2O seemed complicated to me since I'm more familiar in mol/L. So I would no longer use density right?
To solve for the mass of PEG in your 500ml solution, you'll need to use the density of PEG in order to convert the concentration from grams of PEG per kilogram of H2O to grams of PEG per milliliter of solution.
When given a concentration in terms of grams of a solute per kilogram of solvent (in this case PEG/kg H2O), the density you need to use is the density of the solvent (in this case, water or H2O). This is because the concentration is expressed in terms of the mass of solute (PEG) relative to the mass of the solvent (H2O).
So, to calculate the mass of PEG in your solution, you would use the density of water:
?g PEG = 50g PEG/kg H2O x 1kg H2O/1000g x 500 ml x density of H2O
Remember to also convert milliliters to liters (500 ml = 0.5L), and substitute the appropriate value for the density of water (which is approximately 1 g/ml or 1000 g/L).
So, your final equation would be:
?g PEG = 50g PEG/kg H2O x 1kg H2O/1000g x 0.5 L x 1000 g/L