Tenho que limpar o fogão e a pia antes de minha mãe chegar.

Because Portuguese often leaves out subject pronouns when the verb already makes the subject clear. Tenho clearly means I have / I have to because of the verb ending.

So:

• Tenho que limpar... = I have to clean...
• Eu tenho que limpar... = also correct, but eu adds emphasis, contrast, or clarity

A speaker might include eu if they want to stress I specifically:

• Eu tenho que limpar, não você.

Here, tenho que means I have to or I need to. It expresses obligation.

Even though ter usually means to have, the pattern ter que + infinitive is very common and means to have to do something:

• Tenho que limpar = I have to clean
• Temos que sair = We have to leave

In Brazil, tenho que is very natural in everyday speech.

They are very close, but not always identical in tone.

• Tenho que limpar = I have to clean
• Preciso limpar = I need to clean
• Tenho de limpar = also I have to clean

In Brazilian Portuguese:

• tenho que is very common and conversational
• preciso is also very common
• tenho de can sound a little more formal or less common in casual Brazilian speech

So in everyday Brazil, tenho que is an excellent choice.

Because after ter que, the next verb stays in the infinitive.

This is the normal pattern:

• tenho que limpar
• tenho que estudar
• tenho que sair

So limpar is not conjugated because the verb that carries the person and tense is tenho.

Portuguese uses articles more often than English does. In a sentence like this, it is natural to say:

• o fogão = the stove
• a pia = the sink

Even when English might sometimes sound fine without the, Portuguese usually keeps the article.

These articles also show grammatical gender:

• fogão is masculine, so o fogão
• pia is feminine, so a pia

Usually, you learn the noun together with its article:

• o fogão
• a pia

That is the safest habit in Portuguese, because gender is not always perfectly predictable from the ending alone.

For example:

• many words ending in -a are feminine, and pia is feminine
• many words ending in -ão are masculine, and fogão is masculine

But there are exceptions in Portuguese, so it is best to memorize the article with the noun.

Antes de means before when it is followed by a verb.

Examples:

• antes de sair = before leaving
• antes de dormir = before sleeping
• antes de minha mãe chegar = before my mother arrives / before my mother gets here

So the de is required here because antes is followed by a verb phrase.

Because after antes de, Portuguese uses the infinitive, not a normal conjugated verb.

So:

• antes de minha mãe chegar = correct
• antes de minha mãe chega = incorrect

Portuguese can even use an infinitive with its own subject, as in minha mãe chegar.

A useful extra detail: for ela, the personal infinitive looks the same as the regular infinitive, so you still see chegar.

If you want a fully conjugated verb instead, you need a different structure:

• antes que minha mãe chegue

That version is also very natural.

This is about possessives and articles.

In Brazilian Portuguese, you can often say either:

• minha mãe
• a minha mãe

Both can be correct, depending on style, region, and context.

After de, those become:

• de minha mãe
• da minha mãe

In this sentence, antes de minha mãe chegar is a standard, safe version.

You may hear antes da minha mãe chegar in everyday speech, but many teachers and grammar books prefer antes de minha mãe chegar or the alternative antes que minha mãe chegue, especially in more careful writing.

Yes. That is completely natural.

You can say:

• Tenho que limpar o fogão e a pia antes de minha mãe chegar.
• Antes de minha mãe chegar, tenho que limpar o fogão e a pia.

The meaning stays the same. Putting the time expression first can give it a little more emphasis. In writing, a comma is normally used when that clause comes first.

A simple approximation is:

• fogão ≈ foh-GOWN, with a nasal ending
• pia ≈ PEE-ah
• mãe ≈ something like my, but nasalized
• chegar ≈ sheh-GAR in most of Brazil

A few important notes:

• ão in fogão is nasal, which is hard for English speakers at first
• mãe also has a nasal vowel
• ch in Portuguese is usually pronounced like English sh

So the sentence sounds roughly like:

TEN-yo kee leem-PAR oo fo-GOWN ee ah PEE-ah AN-tes djee mee-nyah MYN cheh-GAR

That is only an approximation, but it can help at the beginning.