[chi]

I have questions about preparation of standards for a calibration curve.

I made a 0.40% (weight/volume) ethanol stock solution by diluting 400mg of ethanol with some distilled water in a beaker, then transferred the solution into a 100ml volumetric flask and filled to the line.

By diluting the 0.40% stock solution, I prepared 0.05%, 0.15%, and 0.25% standard ethanol solutions.


Questions:
1. Is it necessary to weigh out exactly 400mg of ethanol? If not, why?
   
2. In preparing the satandards, I just diluted the 0.40% solution to 0.05, 0.15, and 0.25%. Is there a better way to prepare the standards?

[Borek]

What is definition of w/v concentration? It suggests possible ways of preparing the solution.