If I intend to make X ml of Some Salt solution, I dissolve my Salt in about X/2 ml of solvent first, and only then add the rest amount of solvent. As I know adding the whole amount of solvent at once is not right and lead to the biased final concentration.
Why?
As long as the salt is completely soluble in the solvent, it will not affect the final concentration if the volume of the solvent is added all at once or is added step-wise and this relation holds in both cases: Molarity= moles of solute/total volume of solution "in L" . The second choice is favored for this reason:
When the volumetric flask is used for making a solution, the weighed salt will fall from the narrow neck of the flask. Some of the salt may stay at the inner wall of the neck so the solvent is added bit by bit to ensure getting the salt down. Also, the slow addition of solvent " combined with shaking" will guarantee formation of clear solution and reaching the line mark on the neck exactly since this line tells the accurate total volume of the solution.
Hi,
Yes and No. For analytical use:
First you will dissolve your salt in x/2 ml solvent, then you will transfer the solution to volumetric flask , the remain amount of the solvent use it to wash used class wares properly 2-3 times , and add this washing solution to volumetric flask to adjust the meniscus to mark .
Dear Darya Bayramova for a useful description of how to prepare solutions of chemical compounds (e.g. metal salts) please have a look at the following links:
The Preparation of Solutions
https://chem.libretexts.org/Courses/Prince_Georges_Community_College/Chemistry_2000%3A_Chemistry_for_Engineers_(Sinex)/Unit_4%3A_Nomenclature_and_Reactions/Chapter_12%3A_Aqueous_Reactions/Chapter_12.1%3A_Preparing_Solutions
and
Laboratory Solution Preparation
https://www.snc.edu/chemicalhygiene/docs/labsafety/SolutionPrep.pdf
Please note that concentrations are typically given in a solute to solution basis; not in a solute to solvent basis. A rare exception is molality (mol solute / kg solvent).
Instead concentrations, percentage formulation ratios are often given in a solute to solvent basis.
We should generally take not fully specified % concentrations as wt% ― where wt is often omitted or can be substituted by either wt., wt/wt, wt./wt., or m/m.
Note that the salt's water of crystallization (if any) joins to added water once the salt dissolves.
To prepare solutions of a given concentration to exactly fulfill a given volume its density may have to be known. For sufficiently dilute solutions, its density can often be taken as that of water.
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