A chave da senhora está na mesa.

Portuguese often shows possession with de + the owner:

• a chave da senhora = the lady’s key / your key (depending on context)

This is very common and often clearer than sua chave, because sua can be ambiguous in Portuguese. It might mean:

• your
• her
• sometimes even his, depending on context

So da senhora is a more explicit way to say who the key belongs to.

Da is a contraction of:

• de = of
• a = the

So:

• de + a = da

In a chave da senhora, da senhora literally means of the lady.

This kind of contraction is extremely common in Portuguese.

Portuguese uses definite articles much more often than English does.

So where English might say:

• the lady’s key

Portuguese says:

• a chave da senhora

That a inside da comes from the article that goes with senhora.

In Portuguese, nouns like senhora often appear with an article, especially in structures like possession.

Because na is the normal contraction of:

• em = in/on/at
• a = the

So:

• em + a = na

That gives:

• na mesa = on the table

Portuguese regularly contracts prepositions with articles, so em a mesa would sound unnatural.

Portuguese prepositions do not match English one-for-one.

The preposition em can cover meanings that English expresses with:

• in
• on
• at

So:

• na mesa means on the table
• na sala means in the room
• na escola can mean at school

You have to learn the Portuguese preposition as its own pattern, rather than translating word by word.

Portuguese has two main verbs for to be:

• ser → for identity, permanent characteristics, classification
• estar → for location, condition, temporary states

Here the sentence talks about location, so Portuguese uses estar:

• A chave ... está na mesa.

Using é here would be wrong for normal location.

Yes, but it means something different.

• A chave da senhora está na mesa.
  = The lady’s key is on the table.

• A chave está na mesa da senhora.
  = The key is on the lady’s table.

So the position of da senhora matters. It attaches to the noun right before it and changes what is being described.

Senhora is a polite word. Depending on context, it can mean things like:

• lady
• madam
• ma’am
• Mrs.

In Brazilian Portuguese, it is also used as a polite form of you in formal situations. So depending on context, a chave da senhora could refer to:

• the lady’s key
• your key, said politely to a woman

Because nouns in Portuguese have grammatical gender, and chave is a feminine noun.

That is why it takes feminine forms:

• a chave
• da senhora
• na mesa

The grammatical gender of chave does not mean the object itself is biologically female. It is simply part of how the noun behaves in Portuguese grammar.

A simple Brazilian Portuguese approximation is:

• chave → SHAH-vee
• senhora → seh-NYO-rah
• está → es-TAH
• mesa → MEH-zah

A few helpful notes:

• ch in Portuguese sounds like English sh
• nh in senhora sounds like the ny in canyon
• the accent in está shows the stressed syllable: -tá

The accent mark helps show stress and pronunciation.

• está is stressed on the last syllable: es-TAH

In Portuguese, accent marks are not optional decoration. They often tell you:

• which syllable is stressed
• sometimes the vowel quality
• sometimes they help distinguish words

So you should learn the written accent as part of the word.

Yes. Using de to express possession is extremely common in Portuguese.

Examples:

• o carro do meu amigo = my friend’s car
• a bolsa da Maria = Maria’s purse
• a chave da senhora = the lady’s key

Portuguese does have possessive adjectives like meu, minha, seu, sua, but de + noun is often preferred when you want to be clear or specific.