A convenient way to express the mixture of a soluble chemical completely dissolved in water is as a percent solution.  This is  done by weighing out a desired amount of dry chemical and adding water to produce a total given volume.

The following excellent description of solution preparation may be found at the link below.
"Preparation of Solutions for the Clinical Laboratory: A Tutorial"
authored by Kereem M. D. Marlow
http://www.utmem.edu/allied/Solutions/Home.html

Do keep in mind that any material will only dissolve to a certain maximum percentage
for a given temperature and pressure.  Assuming adequate solubility, the following examples demonstrate how to make a percent solution.  (Errors assume using a balance of accuracy 0.01 gram for the solid and a liquid measure accuracy of 0.05 ml.)

example A) To make a 20% solution, weigh 20 grams of soluble solid into a container, then add  water to make a total volume of 100 ml.

example B) To make 60 ml of a 10% solution, weigh 6.00 grams of the soluble solid into a container, then water to make a total volume of  60 ml.

Accuracy:
For smaller quantities, it is more accurate to start with a stronger solution and dilute.

example C) To make 30 ml of a 0.5% solution, make a 10% solution, then add 1.50 ml of the 10% solution with 28.50 ml water.

30 ml of a 0.5% solution would require 0.15 grams.  Weighed on a scale accurate to 0.01 grams, this would have an error of +-6.67%.  In example C, a pipette accurate to .05 ml would produce an error of +-3.33%.
 

It would be even more accurate to work with larger quantities:

example D) To make 30 ml of a 0.5% solution, make a 10% solution, then make a dilution to 2% and then use that to dilute to 0.5%.

For example D, error to make 100 ml of a 10% solution is +-0.1%; error to then make 100 ml of a 2% solution is +-0.25%; error to then make 30 ml of a 0.5% solution is +-0.67%.  Assuming comulative error, the total error would be +-1.02%.
 

It is important to always label a bottle as to its contents and the % solution.
 

Weights and liquid measures and their symbols used in this document:

 

Liquid (volume) measure		Weight measure
ml	= milliliter	g	= gram
liter	= 1000 ml
oz	= ounce = 30 ml
gal	= gallon = 128 oz

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