My problem is I second guess myself when it comes to determining parts of speech in a sentence. Here are the sentences I need opinions on, with the word in question underlined:

Rose petals are one ingredient in potpourri.

Over the weekend my father trimmed the rose bushes.

We go to the park to use the water slide.

Tickets for the rock concert are sold out.

A glass of ice water is so refreshing.

Are these nouns? Or adjectives?

Also, for the sentence "We will be back in one hour", is back the verb?

I thank whomever responds to me!
What do you think they are?
meemskipredicate adjectives
This is a function, not a part of speech. That is, there is no such thing as a part of speech called a "predicate adjective". Emotion: sad
Most of your examples are nouns functioning as adjectives within a compound noun structure. If you need to know these for a class, check with the teacher or your textbook to find out whether, in the grammar system you're using in class, these should be considered nouns or adjectives. (Different textbooks classify these differently.)

The exceptions are water, which is a plain old noun, and back, which is an adverb. Some grammarians might interpret to be back as a phrasal verb, however. Some of these would call back a (phrasal verb) "particle"; others, an adverb.

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I suppose I should be going with my gut instincts with these...

Rose petals, rose bushes, water slide, etc, these are the predicate adjectives

Ice water is a noun....

I am still uncertain about 'we will be back in one hour'.... 'will be' is linking, so I suppose back is the verb.... or 'will' is the link and the action verb is to be back...

Right? English is weird...
 CalifJim's reply was promoted to an answer.
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no back is not the verb. the verb is WILL.