La bolsa de magnesio ya no está vacía.

Because vacía describes a state or condition here, not an essential characteristic.

• estar vacío/a = to be empty
• ser would sound wrong in this sentence

So:

• La bolsa está vacía = The bag is empty.
• La bolsa ya no está vacía = The bag is no longer empty.

In Spanish, estar is commonly used with conditions like:

• está lleno/a = is full
• está abierto/a = is open
• está cerrado/a = is closed
• está roto/a = is broken

Ya no means no longer or not anymore.

So:

• ya no está vacía = is no longer empty / isn’t empty anymore

A very useful pattern is:

• ya no + verb

Examples:

• Ya no vivo allí. = I don’t live there anymore.
• Ya no tengo hambre. = I’m not hungry anymore.
• Ya no llueve. = It’s not raining anymore.

Here, ya adds the idea that something was true before, but now it has changed.

Because vacía agrees with la bolsa, which is a feminine singular noun.

Agreement in Spanish means adjectives change to match the noun:

• el bolso vacío = the empty bag
• la bolsa vacía = the empty bag

Here:

• bolsa is feminine
• singular
• so the adjective must also be feminine singular: vacía

Spanish often uses de where English uses a noun directly before another noun.

So instead of saying something like magnesium bag, Spanish says:

• bolsa de magnesio

This structure is very common:

• taza de café = cup of coffee
• botella de agua = bottle of water
• mesa de madera = wooden table
• clase de español = Spanish class

In other words, de links the two nouns and tells you what kind of bag it is or what it is for / associated with.

Because magnesio is being used in a general/classifying way, not to mean a specific magnesium.

• bolsa de magnesio = a magnesium bag / chalk bag
• bolsa del magnesio would sound like the bag of the magnesium, referring to some specific magnesium already identified

After de, Spanish often omits the article when the second noun is naming a type or category:

• zapatos de cuero = leather shoes
• vaso de cristal = glass cup
• bolsa de magnesio = chalk/magnesium bag

So de magnesio here means for magnesium / containing magnesium / associated with magnesium, not of the specific magnesium.

More or less, yes. Bolsa is a general word for bag, pouch, or sack, depending on context.

In this sentence, bolsa de magnesio usually refers to the small bag/pouch used for climbing, gymnastics, or weightlifting chalk.

A few related words:

• bolsa = bag, sack, pouch
• bolso = handbag / purse
• mochila = backpack

So bolsa is the natural word here, not bolso.

The accent mark shows where the stress falls and helps keep the vowels separate.

vacía is pronounced with -cí-a as three syllables:

• va-cí-a

Without the accent, Spanish spelling rules would suggest a different stress pattern.

This happens in many words where í or ú forms its own syllable:

• vacío
• frío
• tía
• día

So the accent in vacía is both a pronunciation guide and a spelling requirement.

It is much more natural to say:

• La bolsa de magnesio ya no está vacía.

The structure ya no + verb is the normal pattern for no longer.

While Spanish word order can vary, ya no está is the standard, most natural order here.

So for learners, it is best to remember:

• ya no es
• ya no está
• ya no tengo
• ya no puedo

as fixed, common patterns.

In a full sentence like this, the article is normally needed:

• La bolsa de magnesio ya no está vacía.

Spanish uses articles more often than English. If you remove la, the sentence sounds incomplete in normal usage.

You might omit the article only in special contexts, such as:

• labels
• headings
• notes
• very telegraphic instructions

But in ordinary speech or writing, la is expected.

Not exactly.

• ya no está vacía = it is no longer empty
• está llena = it is full

If something is no longer empty, it now contains something, but it may not be completely full.

So:

• Ya no está vacía is a weaker statement.
• Está llena is stronger and more specific.

Yes, in Spain people commonly say magnesio in sports contexts such as climbing, gymnastics, or weightlifting, even though the substance is not literally pure magnesium metal.

So in real usage:

• magnesio often refers to the white chalk-like powder used on the hands
• bolsa de magnesio is the normal expression for a chalk bag

This is a good example of how everyday vocabulary can be a little different from strict scientific terminology.