Question

What is a standard solution?

Answer 1

A solution whose concentration is known to a great degree of precision and correctness.

Explanation:

In analytical chemistry, all of the methods envolved - except gravimetry - require either a solution of known concentration either for a direct reaction (titrometric methods) or for a calibration curve (other methods), so we use standard solutions.

They may be primary standards - i.e.: solutions of salts that can be obtained in extremely high purity, such as `NaCl`, `K_2CrO_7`, `CaCO_3` or `Na_2H_2Y_2` (EDTA) - or secondary standards - solutions that were analyzed using a primary standard.

And they may be either made "in-house" so to speak or be bought from another lab - generally with a certificate of purity.