Hiệu thuốc đã đóng, nên tôi sẽ mua thuốc vào sáng mai.

Yes. Hiệu thuốc means pharmacy / drugstore.

In this sentence:

• hiệu = shop/store (an older or somewhat formal/literary word in some combinations)
• thuốc = medicine

So hiệu thuốc literally means medicine shop.

In modern everyday Vietnamese, many people also say:

• nhà thuốc = pharmacy
• tiệm thuốc = drugstore/pharmacy

All of these can work, though nhà thuốc is especially common in modern usage.

Đã often marks that something has already happened or is completed.

So:

• đóng = close / be closed
• đã đóng = has closed / is already closed

In this sentence, đã does not just mean simple past tense. It emphasizes that the closing has already happened, and that is why the speaker cannot buy medicine now.

So Hiệu thuốc đã đóng is very naturally understood as:

• The pharmacy has already closed
• or The pharmacy is closed already

It can function like both, depending on context.

In Vietnamese, many words do not change form the way English verbs and adjectives do. So đóng can mean:

• to close
• closed

In Hiệu thuốc đã đóng, it means the pharmacy has closed / is closed.

Compare:

• Tôi đóng cửa. = I close the door.
• Cửa đã đóng. = The door is closed / has been closed.

So the meaning comes from the sentence context, not from a different word ending.

Vietnamese does not normally use articles like the or a/an the way English does.

So:

• hiệu thuốc can mean the pharmacy, a pharmacy, or just pharmacies in some contexts

Here, the context makes it natural to translate it as the pharmacy.

This is very common in Vietnamese: you usually understand definiteness from the situation, not from an article.

Nên means so, therefore, or thus.

It connects the first clause to the result:

• Hiệu thuốc đã đóng = The pharmacy has already closed
• nên tôi sẽ mua thuốc vào sáng mai = so I will buy medicine tomorrow morning

So nên introduces the consequence.

A very common pattern is:

• ..., nên ... = ..., so ...

Sẽ is a future marker. It often means will or going to.

So:

• tôi mua thuốc = I buy / I am buying / I buy medicine
• tôi sẽ mua thuốc = I will buy medicine

In Vietnamese, future time can sometimes be understood without sẽ if the time expression already makes it clear. For example:

• Tôi mua thuốc sáng mai can still be understood as I’ll buy medicine tomorrow morning

But sẽ makes the future meaning clearer and more explicit, much like will in English.

Here vào is a time marker meaning something like in, on, or at, depending on what sounds natural in English.

So:

• vào sáng mai = tomorrow morning

More literally, it is something like in/on tomorrow morning, but English would usually just say tomorrow morning.

You will often see vào before time expressions:

• vào ngày mai = tomorrow
• vào buổi tối = in the evening
• vào tháng sau = next month

In many cases, vào is optional, especially in everyday speech.

Yes, absolutely.

Both are natural:

• Tôi sẽ mua thuốc sáng mai.
• Tôi sẽ mua thuốc vào sáng mai.

The version with vào can sound a little more structured or explicit, but both are correct.

In casual speech, people often leave vào out when the time expression is already clear.

Because the two uses mean different things in different expressions:

• hiệu thuốc = pharmacy/drugstore
• mua thuốc = buy medicine

So even though the word thuốc appears twice, it is doing two different jobs:

1. as part of the compound noun hiệu thuốc
2. as the object medicine

This repetition is completely normal in Vietnamese.

Mostly yes.

The sentence structure is:

• Hiệu thuốc đã đóng
  subject + aspect marker + verb/state
• nên tôi sẽ mua thuốc vào sáng mai
  so + subject + future marker + verb + object + time

A fairly literal English-style order would be:

• The pharmacy has already closed, so I will buy medicine tomorrow morning.

So the overall order is quite close to English in this example.

Because Vietnamese does not need a dummy subject like English it.

English often says:

• It is raining
• It is late

Vietnamese does not use a meaningless subject like it there.

In this sentence, the first clause already has a real subject:

• Hiệu thuốc = the pharmacy

So Hiệu thuốc đã đóng is complete by itself: The pharmacy has closed / is closed.

Yes, and this is very common.

They refer to different clauses:

• đã đóng = already closed
• sẽ mua = will buy

So the sentence contrasts:

• a present result caused by an earlier event
• a future action that follows from it

That is why the combination feels very natural:

• The pharmacy has already closed, so I will buy medicine tomorrow morning.

Yes. Some possible alternatives are:

• vì ... nên ... = because ... so ...
• cho nên = therefore / so
• sometimes just a comma in speech or writing, if the relationship is obvious

For example:

• Vì hiệu thuốc đã đóng, nên tôi sẽ mua thuốc vào sáng mai.
• Hiệu thuốc đã đóng, cho nên tôi sẽ mua thuốc vào sáng mai.

But the original sentence with just nên is simple and very natural.

It is mostly neutral and perfectly standard.

A few notes:

• hiệu thuốc is understandable and correct, though nhà thuốc may sound more common in modern everyday speech in many places.
• The grammar itself is neutral and standard.
• The sentence sounds natural in conversation and writing.

A slightly more everyday version might be:

• Nhà thuốc đóng rồi, nên tôi sẽ mua thuốc vào sáng mai.

But the original sentence is still good Vietnamese.