tā huíjiā de shíhou shùnbiàn qù yàodiàn mǎi le xīn de kǒuzhào.

回家的时候 literally means the time of going home / when (she) was going home.

A useful pattern is:

• verb phrase + 的时候 = when / while / at the time that ...

So here:

• 回家 = to go home
• 回家的时候 = when going home or when she was on her way home

In this sentence, it sets the time background for the main action:

• 她回家的时候，顺便去药店买了新的口罩。
• When she was going home, she stopped by the pharmacy and bought new masks.

This pattern is very common in Mandarin:

• 吃饭的时候 = when eating
• 下班的时候 = when getting off work
• 睡觉的时候 = when sleeping / at bedtime

In Mandarin, the subject is often omitted when it is already clear from context.

The full meaning is understood as:

• 她回家的时候 = when she was going home

Chinese often avoids repeating the subject if the sentence is still clear. Since the whole sentence starts with 她, readers naturally understand that she is also the person going home.

So this is very normal Chinese, not incomplete Chinese.

顺便 means conveniently, while you’re at it, or on the way / in passing.

It describes doing something extra without making it a separate major trip or effort.

In this sentence:

• 顺便去药店买了新的口罩
• (she) conveniently stopped by the pharmacy to buy new masks

The idea is:

• she was already going home
• going to the pharmacy was an extra thing she did along the way

Common uses of 顺便:

• 你去超市的话，顺便帮我买瓶水。 If you’re going to the supermarket, pick up a bottle of water for me on the way.
• 我顺便问一下。 Let me ask one more thing while I’m at it.

Because 顺便 works like an adverb here, and adverbs usually come before the verb phrase they modify.

So:

• 顺便去药店买了新的口罩
• conveniently / on the way went to the pharmacy to buy new masks

The structure is roughly:

• subject + time phrase + adverb + verb phrase

Here:

• 她 = subject
• 回家的时候 = time phrase
• 顺便 = adverb
• 去药店买了新的口罩 = verb phrase

This placement is very natural in Chinese.

去 means to go, and it shows movement to the pharmacy.

So:

• 去药店 = go to the pharmacy
• 去药店买口罩 = go to the pharmacy to buy masks

Without 去, the sentence would lose the clear idea of physically going there.

Compare:

• 去药店买口罩 = go to the pharmacy to buy masks
• 在药店买口罩 = buy masks at the pharmacy

So 去 focuses on the movement there, while 在 would focus on the location where the buying happens.

Here, 了 marks the action as completed.

• 买了 = bought
• 买 by itself = buy / to buy

So:

• 买了新的口罩 = bought new masks

In this sentence, 了 tells us that she actually completed the purchase, not just intended to buy them.

Compare:

• 她去药店买新的口罩。 She goes/is going to the pharmacy to buy new masks.
  This can sound more like a plan, habit, or general statement.

• 她去药店买了新的口罩。 She went to the pharmacy and bought new masks.
  This sounds like a completed event.

Yes, both 新的口罩 and 新口罩 are possible, but they are not always exactly the same in tone.

In this sentence:

• 新的口罩 sounds very natural and common.
• It means new masks.

About 的

When an adjective modifies a noun, 的 is often used, especially when the modifier feels a bit more descriptive or emphasized.

• 新的口罩 = new masks

Can 新口罩 work?

Yes, sometimes. Chinese often omits 的 with simple, closely connected adjective-noun combinations, especially in shorter, more fixed-sounding phrases.

But in many everyday sentences, 新的口罩 sounds smoother and more standard than 新口罩.

A simple learner rule:

• both can exist
• adjective + 的 + noun is very safe
• with very common short combinations, 的 may be omitted

Examples:

• 新的手机 = a new phone
• 新手机 = new phone / a new-model phone

Sometimes the version without 的 can sound a little more like a category or label, while the version with 的 sounds more plainly descriptive.

Because the sentence is talking about masks in general, not a specific number.

Chinese does not always need a measure word before a noun. A measure word is required mainly when a noun comes after:

• a number
• a demonstrative such as 这 or 那

For example:

• 三个口罩 = three masks
• 这些口罩 = these masks

But in this sentence:

• 买了新的口罩
• bought new masks

There is no number like three, and no demonstrative like these, so no measure word is needed.

This is similar to English plural nouns used generally:

• bought masks
• bought books
• bought fruit

Yes. 药店 usually means pharmacy or drugstore.

In many contexts, translating it as pharmacy is best. It is a shop where you buy medicine and often other health-related items, such as:

• masks
• thermometers
• vitamins
• basic medical supplies

So in this sentence, buying 口罩 at a 药店 makes perfect sense.

口罩 means mask, usually a face mask worn over the mouth and nose.

In modern everyday usage, it often refers to:

• medical masks
• disposable masks
• protective face masks

So:

• 新的口罩 = new masks

If context matters, English might translate it as:

• new face masks
• new masks

Usually, 回家的时候 here is understood as when she was going home or on her way home, especially because the next action is 去药店买了新的口罩.

That flow suggests:

1. she was heading home
2. along the way, she stopped at the pharmacy
3. she bought new masks

If you wanted to emphasize after arriving home, Chinese would usually say something different, such as:

• 她回到家以后... = after she got home...
• 她到家以后... = after arriving home...

So in this sentence, 回家的时候 is best understood as while heading home.

Yes, very common. The sentence follows a very natural Chinese order:

• subject
• time/background
• adverb
• main action
• object

So here we get:

• 她 = she
• 回家的时候 = when she was going home
• 顺便 = on the way / conveniently
• 去药店买了 = went to the pharmacy and bought
• 新的口罩 = new masks

A rough structure formula is:

• Subject + Time phrase + Adverb + Verb phrase + Object

This kind of organization is extremely common in Mandarin, especially placing time information early in the sentence.