Ten cuidado con ese vaso de vidrio, que puede romperse.

Because ten is the tú imperative form of tener, so it means be careful or literally have care.

• tienes cuidado = you are careful / you have care
• ten cuidado = be careful!

This is a very common fixed expression in Spanish:

• Ten cuidado = Be careful
• Tenga cuidado = Be careful (formal, usted)
• Tened cuidado = Be careful (plural informal in Spain, vosotros)
• Tengan cuidado = Be careful (plural formal / general Latin American ustedes)

Spanish often expresses ideas with a verb + noun combination where English uses an adjective.

So instead of saying something literally like be careful, Spanish commonly says have care:

• tener cuidado = to be careful / to take care

This is just the normal idiomatic way to say it. You will hear it very often.

Because tener cuidado is a fixed idiomatic expression, and it normally appears without an article.

So:

• ten cuidado = correct
• ten el cuidado = not natural here

Spanish has many expressions like this where English learners may expect an article, but native usage simply does not include one.

Ese is a demonstrative adjective meaning that.

Spanish traditionally makes a three-way distinction:

• este = this (near the speaker)
• ese = that (near the listener, or not especially near the speaker)
• aquel = that over there (far from both)

So ese vaso means that glass.

In real conversation, the exact physical-distance distinction is not always strict, but this is the general idea.

A vaso is a drinking glass / tumbler / cup-like container, but it does not always have to be made of glass. It could also be plastic, paper, etc.

So vaso de vidrio specifies the material:

• vaso = drinking glass / tumbler
• vaso de vidrio = glass made of glass

This can sound a little redundant in English, but it is perfectly normal in Spanish when the material matters.

These words are not interchangeable.

• vaso = a regular drinking glass / tumbler
• copa = a stemmed glass, like a wine glass
• taza = a cup, usually for coffee or tea

So in this sentence, vaso is the natural word if we mean an ordinary drinking glass.

Spanish very often expresses material with de + material:

• de vidrio = made of glass
• de madera = made of wood
• de papel = made of paper
• de metal = made of metal

So vaso de vidrio literally means glass/cup of glass, i.e. a glass made of glass.

This is one of the most common ways to describe what something is made of.

The comma shows that que puede romperse is adding extra information about ese vaso de vidrio.

Here, que means something like which:

• ese vaso de vidrio, que puede romperse = that glass, which can break

This type of clause is often called an explanatory relative clause. It gives additional information, almost like a side comment explaining why you should be careful.

So the whole sentence has the feel of:

• Be careful with that glass, since it could break.

Here que introduces a clause referring back to ese vaso de vidrio, so it works like which or that in English:

• ese vaso de vidrio, que puede romperse = that glass, which can break

Because of the comma and the overall meaning, the clause also gives a reason, so in natural English it may feel close to:

• because it can break
• since it can break

But grammatically, it is not exactly the same as porque. It is still a relative clause attached to vaso.

Yes, you could say:

• Ten cuidado con ese vaso de vidrio porque puede romperse.

This is also correct and sounds very natural. It makes the reason more explicit:

• Be careful with that glass because it can break.

The original version with , que puede romperse sounds slightly more like an added explanatory comment. Both are good, but the nuance is a little different.

Romper means to break something.

• romper un vaso = to break a glass

Romperse means to break in the sense of to get broken / to break itself / to become broken.

• El vaso puede romperse = The glass can break
• El vaso se rompió = The glass broke

So the se here helps make the verb intransitive: the glass is not breaking something else; the glass itself may end up broken.

The se is part of the verb form used when something breaks rather than breaks something.

Compare:

• Rompí el vaso. = I broke the glass.
• El vaso se rompió. = The glass broke.

In the sentence puede romperse, the idea is:

• it can break
• it can get broken

This is a very common pattern in Spanish with changes of state:

• abrir = to open something
• abrirse = to open
• cerrar = to close something
• cerrarse = to close
• romper = to break something
• romperse = to break

Yes. Both are correct:

• puede romperse
• se puede romper

They mean essentially the same thing here: it can break.

In everyday Spanish, both word orders are common. The choice is usually about style, rhythm, or emphasis rather than meaning.

Because Spanish often leaves out subject pronouns when they are already clear from the verb form.

In commands, this is especially common:

• Ten cuidado = Be careful
• Tú ten cuidado = possible, but more emphatic

You would only add tú if you wanted extra emphasis, contrast, or clarity.

It is informal singular, because ten is the tú command.

If you wanted to speak formally to one person, you would say:

• Tenga cuidado con ese vaso de vidrio, que puede romperse.

So:

• ten = informal singular
• tenga = formal singular

Yes, it is natural and correct in Spain Spanish.

A Spaniard might also say similar versions such as:

• Ten cuidado con ese vaso, que se puede romper.
• Cuidado con ese vaso, que es de vidrio.
• Ten cuidado con ese vaso de cristal.

All of these sound natural, though they differ slightly in wording.

Often, yes. In everyday Spanish, especially in Spain, cristal is very commonly used for glass as a material.

So you may hear:

• vaso de cristal

This can sound even more everyday than vaso de vidrio in some contexts.

Very roughly:

• vidrio = glass as a material, a bit more technical/literal
• cristal = very common everyday word for glass objects/material in many contexts

But both can be understood.

Spanish poder covers both ideas depending on context:

• ability: can
• possibility: may / might / can

Here puede romperse means it can break or it could break, meaning it is possible that it breaks.

So puede is expressing possibility, not permission.

Yes, that is the implication.

The speaker is warning someone to be careful because the object is breakable. The sentence does not directly say it is fragile, but that is the practical idea behind the warning.

It refers to ese vaso de vidrio.

The thing that can break is the glass, not the person.

This is clear from meaning, and also from the structure of the sentence: the relative clause introduced by que attaches to the noun phrase right before it, ese vaso de vidrio.