Why is pure sulfuric acid unsuitable for direct standard solution preparation?

[jadelamlam]

titration-->pure sulphuric acid

Homework Statement

Why pure/conc. sulphuric acid is not suitable to prepare a standard solution directly?

Homework Equations

The Attempt at a Solution

I know that it is hygroscopic,but what does it mean?Why absorbing moisture from the air will affect the result of titration?

 

[Borek]

http://www.titrations.info/titration-standard-substances