A tigela na qual misturei o limão tem tampa, mas agora vou destapá‑la.

Yes.

• A tigela em que misturei o limão… is the most neutral, everyday choice.
• A tigela onde misturei o limão… is also very common; although strictly spatial, Portuguese often uses onde with containers/places.
• A tigela na qual… is correct but sounds more formal or written.

Because the verb pattern is essentially “mix X in Y,” which requires the preposition em before the relative. You need to keep the preposition:

• ✅ A tigela em que/na qual misturei o limão…
• ❌ A tigela que misturei o limão… (missing the needed preposition)

European Portuguese typically places clitics after infinitives and gerunds, and after many finite verbs in affirmative clauses. With a periphrastic future like vou + infinitive, the default is to attach the pronoun to the infinitive:

• ✅ Vou destapá‑la.
• Less common in EP: Vou‑a destapar.

When attaching the direct‑object pronouns o, a, os, as to a verb that ends in ‑r, ‑s, or ‑z, Portuguese:

• drops that final consonant, and
• turns the pronoun into ‑lo, ‑la, ‑los, ‑las. So: destapar + a → destapá‑la.

Adding the clitic creates an extra syllable that would otherwise shift the stress. The accent marks the intended stress and preserves the original stress of the verb:

• destapar → des‑ta‑PAR (stress on the last syllable)
• • ‑la → des‑ta‑PÁ‑la (accent keeps the stress where it belongs)

Other examples:

• fazer + o → fazê‑lo
• comer + as → comê‑las
• amar + os → amá‑los

Both forms are used in European Portuguese:

• Não a vou destapar. (proclisis to the auxiliary; very common and “safer” in writing)
• Não vou destapá‑la. (clitic on the infinitive; also widely heard)

Formally, ‑la just marks “feminine singular,” so it could match either a tigela or a tampa. But idiomatically you normally destapar a tigela/panela, not “destapar a tampa” (you’d say tirar a tampa for the lid). So here ‑la most naturally refers to a tigela.

To remove ambiguity you could say:

• …mas agora vou destapar a tigela.
• Or, if you mean the lid: …mas agora vou tirar a tampa.

It’s fine and means you mixed “the lemon” (as an ingredient). If you want to be explicit, you can say o sumo de limão (lemon juice) or name what you mixed it with:

• Misturei o limão em/na tigela.
• Misturei o sumo de limão com açúcar.

Common patterns:

• misturar X com Y = mix X with Y
• misturar X em Y / na Y = mix X into/in Y (container) Hence the need for em in the relative clause: na qual/em que.

Not here. Aonde is used for motion (“to where”). You’re talking about location within a container, so use onde or em que/na qual:

• ✅ A tigela onde/em que/na qual misturei…
• ❌ A tigela aonde misturei…

Agreement adapts:

• Feminine plural: As tigelas nas quais misturei… vou destapá‑las.
• Masculine singular: O recipiente no qual… vou destapá‑lo.
• Masculine plural: Os recipientes nos quais… vou destapá‑los.

Yes, for everyday speech:

• Misturei o limão na tigela. Ela tem tampa, mas agora vou destapá‑la. Or even:
• Misturei o limão na tigela, que tem tampa, mas agora vou destapá‑la.