HCl as a Primary Standard?

Question: Why is HCl not suitable as a primary standard?
Answer:  There are three main reasons why HCl is not suitable as a primary standard:

• HCl is not a solid at room temperature and pressure. 
• HCl cannot be obtained at a very high purity.
• HCl does not have a high molecular mass.

You can find out more about what makes, and does not make, a primary standard at:
http://www.ausetute.com.au/titrstand.html