using "them" or "it" as a pronoun for uncountable noun

I'm an English learner. I have a question relating to using pronouns. Here's my example sentence:

Yesterday I bought some furniture for my kitchen. Some of them is so expensive.

I don't know if I should use "them" or "it." And is "is" correct or not?

Answer

We don't use plural pronouns for mass nouns. Furniture is treated as a mass (or uncount or noncount) noun. See Cambridge.

This might seem counter-intuitive since most people can count individual pieces of furniture.

Here's an example with another mass noun, milk:

Yesterday I bought some milk for the new refrigerator. Some of it is on the top shelf. I put the rest of it on the bottom shelf.