Breakdown of Я должен надеть очки, чтобы безопасно смешивать эти вещества.
я
I
этот
this [f: эта, n: это]
очки
glasses
должен
must, have to
Questions & Answers about Я должен надеть очки, чтобы безопасно смешивать эти вещества.
Why is надеть perfective, but смешивать imperfective?
You need to perform a single, completed action first: putting the glasses on (надеть). But the mixing itself is an ongoing, continuous process, so we use the imperfective смешивать.
Could I use одеть instead of надеть here?
No. A classic rule in Russian is that you use одеть to dress someone else (like a child), but надеть to put an item of clothing or an accessory on yourself. Since you are putting on glasses, it must be надеть.
Why is смешивать in the infinitive after чтобы?
When the subject of the main action (I must put on) is exactly the same as the subject of the purpose action (in order for me to mix), чтобы is always followed by an infinitive.
What case is эти вещества in, and why?
It is in the accusative plural because it is the direct object of the verb смешивать. Because вещество (substance) is an inanimate neuter noun, its accusative plural form is identical to its nominative plural.