I sometimes see one word where the other word is required.

Problem:
These two nouns are not synonyms.

Explanation:
The noun “albumen” refers to the white of an egg.

The noun “albumin” refers to the water-soluble protein found in the whites of eggs, in milk, in boold,

Solution:
Use “albumen” to refer to the white of an egg. A way to remember this is the common “e” in “albumen” and “egg”. Use “albumin” to refer to the protein that occurs in egg whites, blood, milk, etc. A way to remember this is the common “i” in “albumin” and “protein”.