Ilość szkła jest duża.

Both words can mean amount/number, but they are used differently:

• liczba = number of countable things
  
  • e.g. liczba studentów = the number of students
• ilość = amount/quantity of something that is usually treated as uncountable or as a mass
  
  • e.g. ilość wody = the amount of water

In Ilość szkła jest duża, szkło means glass as a material, so it is being treated as something uncountable. That is why ilość fits better than liczba.

After nouns like ilość (amount, quantity), Polish normally uses the genitive case.

So:

• szkło = nominative
• szkła = genitive

This is very common in Polish:

• ilość wody = amount of water
• dużo czasu = a lot of time
• mało pieniędzy = little money

So ilość szkła literally works like quantity of glass.

Because duża agrees with ilość, not with szkła.

The subject of the sentence is ilość:

• ilość is feminine singular
• so the adjective must also be feminine singular
• therefore: duża

Compare:

• Ilość jest duża.
• Liczba jest duża.

You do not use dużo here, because dużo is usually an adverb/quantifier meaning a lot, not an adjective agreeing with a noun in this kind of sentence.

In this kind of sentence, jest is normally required.

Polish often omits to be in the present tense only in some sentence types, especially where two nouns are linked in an equational way in informal style. But with an adjective like duża, you normally say:

• Ilość szkła jest duża.

Without jest, it would sound incomplete or unnatural.

Szkło most often means glass as a material.

So in this sentence, it means there is a large amount of the material glass, not necessarily many glasses as drinking vessels.

Polish distinguishes:

• szkło = glass, the material
• szklanka = drinking glass / tumbler

However, in some contexts szkło can also refer more generally to glassware or broken glass, depending on the situation. But the basic meaning here is the material.

It is grammatical and understandable, but it can sound a bit formal, measured, or report-like.

In everyday speech, people often prefer:

• Jest dużo szkła. = There is a lot of glass.

That version sounds more natural in ordinary conversation.

Ilość szkła jest duża is more likely in:

• formal description
• reports
• technical writing
• scientific or analytical contexts

So yes, it is correct, but it is not always the most casual way to say it.

Yes. The neutral order here is:

• Ilość szkła jest duża.

But Polish word order is flexible, and different orders can shift emphasis:

• Duża jest ilość szkła.
  More marked; emphasizes duża
• Jest duża ilość szkła.
  Also possible; a bit closer to There is a large amount of glass

The standard, neutral version for learners is still:

• Ilość szkła jest duża.

Yes. That is a noun phrase, not a full sentence:

• duża ilość szkła = a large amount of glass

If you turn it into a full sentence, you can say:

• Duża ilość szkła jest tutaj. = A large amount of glass is here.
• To jest duża ilość szkła. = That is a large amount of glass.

So:

• ilość szkła jest duża = the amount of glass is large
• duża ilość szkła = a large amount of glass

They are closely related, but not exactly the same structure.

Often, yes, in practical meaning.

• dużo szkła = a lot of glass
• ilość szkła jest duża = the amount of glass is large

The difference is mostly style and structure:

• dużo szkła is more common in everyday speech
• ilość szkła jest duża is more formal and abstract

For example:

• Na podłodze jest dużo szkła. = There is a lot of glass on the floor.
• Ilość szkła na podłodze jest duża. = The amount of glass on the floor is large.

The second sounds more analytical.

A rough pronunciation guide is:

• Ilość ≈ EE-loshch
• szkła ≈ shkwah
• jest ≈ yest
• duża ≈ DOO-zhah

A few useful points:

• ś is a soft sh-like sound
• ć is a soft ch-like sound
• in -ość, the ending is compressed and can be tricky for English speakers
• sz sounds like English sh
• ż sounds like the s in measure

A more connected approximation: EE-loshch shkwah yest DOO-zhah

Because szkło here is being treated as a mass noun, like English glass, water, or sand.

Even if physically there are many pieces, Polish can still talk about the substance as one uncountable material:

• dużo szkła = a lot of glass
• mało szkła = little glass

If you wanted to focus on separate objects, you would usually use different wording, for example a countable noun referring to bottles, panes, glasses, etc.

So the sentence is about the quantity of the material, not the number of individual items.

Yes. In this sentence, ilość szkła is the full subject phrase.

More specifically:

• head noun: ilość
• dependent genitive noun: szkła
• predicate: jest duża

So grammatically, the sentence is built around ilość. That is why the verb and adjective are singular:

• jest
• duża

They agree with ilość, not with szkła.

Yes, very easily. This is a very common pattern:

• Ilość + genitive + jest + adjective

Examples:

• Ilość wody jest mała. = The amount of water is small.
• Ilość pracy jest ogromna. = The amount of work is enormous.
• Ilość informacji jest wystarczająca. = The amount of information is sufficient.

So Ilość szkła jest duża is a good model for learning how Polish expresses amount of X is Y.