Hi ha molta cua a la farmàcia, per això la meva mare arribarà tard.

Hi ha is the standard Catalan way to say there is or there are.

• Hi is an adverb-like element that is part of this fixed expression.
• Ha is from the verb haver.

So:

• Hi ha una farmàcia = There is a pharmacy
• Hi ha dues farmàcies = There are two pharmacies

In your sentence, Hi ha molta cua means There is a long queue / There are a lot of people waiting.

A useful point: hi ha does not change between singular and plural in standard Catalan. It stays hi ha for both there is and there are.

Because cua is a feminine singular noun, and molt has to agree with it.

Agreement forms:

• molt = masculine singular
• molta = feminine singular
• molts = masculine plural
• moltes = feminine plural

So:

• molta cua = a lot of queue / a long line
• molta gent = a lot of people
• molt temps = a lot of time

This is normal adjective/determiner agreement in Catalan.

Yes, cua literally means tail, but it also commonly means queue, line.

So in everyday Catalan:

• fer cua = to stand in line / queue
• hi ha cua = there is a line
• molta cua = a long line / a lot of waiting line

This is very natural in Catalan, just as English uses line in a figurative way.

Here a la farmàcia means at the pharmacy.

The preposition a can correspond to several English prepositions depending on context, especially:

• to
• at
• sometimes in/on in certain expressions

In this sentence, because it describes where the queue is, the meaning is at the pharmacy:

• Hi ha molta cua a la farmàcia = There is a long line at the pharmacy

If the focus were movement, a could mean to:

• Vaig a la farmàcia = I’m going to the pharmacy

So the exact English translation depends on the situation.

Yes. Per això means because of that, for that reason, or more naturally in English, that’s why.

It links the first idea to the result:

• Hi ha molta cua a la farmàcia, per això la meva mare arribarà tard.
• There’s a long line at the pharmacy, that’s why my mother will arrive late.

You can think of it as a connector meaning therefore / so / that’s why.

A closely related structure is:

• Per això... = That’s why...

It is very common in spoken and written Catalan.

Because Catalan usually uses the definite article before a possessive and a family noun:

• la meva mare = my mother
• el meu pare = my father
• la meva germana = my sister

This is different from English, where you normally say just my mother.

So the pattern is often:

• article + possessive + noun

Examples:

• el meu cotxe = my car
• la nostra casa = our house

With close family terms, this article is especially common and natural.

Catalan often omits subject pronouns because the verb ending already shows who the subject is.

Here:

• arribarà already means he/she/it will arrive

So la meva mare arribarà tard is perfectly clear, and adding ella is unnecessary unless you want emphasis or contrast.

Compare:

• La meva mare arribarà tard. = neutral
• Ella arribarà tard. = she will arrive late
• La meva mare, ella arribarà tard. = marked/emphatic, not the most neutral version here

Like Spanish and Italian, Catalan is a pro-drop language.

Arribarà is the simple future of arribar (to arrive).

Conjugation of the future is based on the infinitive:

• arribaré = I will arrive
• arribaràs = you will arrive
• arribarà = he/she will arrive
• arribarem = we will arrive
• arribareu = you all will arrive
• arribaran = they will arrive

So:

• la meva mare arribarà tard = my mother will arrive late

This is the normal future tense, not a periphrastic construction.

Because here tard is an adverb, meaning late.

In the expression:

• arribar tard = to arrive late

tard does not agree with anything. It stays the same.

Compare:

• Ha arribat tard. = He/She arrived late.
• Arribarem tard. = We will arrive late.

Do not confuse this with tarda, which is the noun meaning afternoon.

So:

• tard = late
• tarda = afternoon

They are different words.

It is very natural, and usually appropriate, because per això introduces a consequence based on the first clause.

So the sentence is naturally divided into two parts:

1. Hi ha molta cua a la farmàcia
2. per això la meva mare arribarà tard

The comma helps show that relationship clearly.

In informal writing, punctuation can vary, but with this kind of connector, the comma is a good standard choice.

Yes, and both are natural, but they are not exactly identical in nuance.

• Hi ha molta cua suggests there is a lot of queue / a big line / a lot of waiting
• Hi ha una cua molt llarga means there is a very long line

The first is a very common idiomatic way to talk about queueing. The second describes the line more explicitly.

So both work, but molta cua is especially idiomatic in everyday Catalan.

The original sentence is already very natural Catalan. The order is:

• situation first: Hi ha molta cua a la farmàcia
• consequence next: per això la meva mare arribarà tard

This is a very common structure.

Catalan does allow some flexibility, but not every rearrangement sounds equally natural. For example:

• Hi ha molta cua a la farmàcia, per això la meva mare arribarà tard. = very natural
• La meva mare arribarà tard, perquè hi ha molta cua a la farmàcia. = also very natural, but now it uses perquè (because)
• Per això la meva mare arribarà tard can also stand at the beginning if the context is already clear

So yes, there is some flexibility, but the given sentence is a standard, idiomatic way to say it.