Learn Italian: Questa chiave è nuova.

While most feminine nouns end in -a, Italian has a whole category of nouns that end in -e in the singular. These words can be either masculine or feminine, and you just have to memorize their gender when you learn them. Chiave (key) happens to be one of the feminine ones!

If chiave ends in -e, why do questa and nuova end in -a?

Words that describe the noun, like questa (this) and nuova (new), must match the noun's gender. Because chiave is feminine, those describing words take the standard feminine singular ending -a. They don't copy the noun's exact vowel; they just match its feminine gender.

How would I make this sentence plural ("These keys are new")?

You would say, Queste chiavi sono nuove. Nouns from the -e group (like chiave) always change to -i in the plural. Meanwhile, the standard feminine words questa and nuova change their -a endings to -e (queste, nuove), and è (is) becomes sono (are).

Why is there an "h" in chiave?