Ипотека кажется страшной, но мы взяли её, потому что хотели свою квартиру.

After казаться (and similar verbs like быть, становиться), Russian often uses the instrumental case for the “predicate” adjective describing how something seems/turns out.

• Ипотека (subject, nominative)
• кажется (seems)
• страшной = instrumental feminine singular of страшная (страшной)

You may also see nominative in some contexts, but instrumental is the most common/neutral with казаться.

кажется means (it) seems / appears. Grammatically, ипотека is the thing that “seems,” and the person judging is implied (here: to us).

If you want to state the observer explicitly, you can add a dative pronoun:

• Ипотека нам кажется страшной = The mortgage seems scary to us.

Because но (but) joins two independent clauses: 1) Ипотека кажется страшной
2) но мы взяли её...

In Russian, you normally put a comma before но in this structure.

Because потому что introduces a subordinate clause of reason. Russian typically separates the main clause from the reason clause with a comma:

• мы взяли её, потому что хотели...
  = we took it, because we wanted...

её is the accusative form of она (her/it), and it refers back to ипотека (a feminine noun), meaning we took it / we got it (i.e., took out the mortgage).

Note: её doesn’t change for case (it looks the same in genitive/accusative), but here it’s functioning as the direct object of взяли.

Yes. In Russian, the common collocation is:

• взять ипотеку = to take out a mortgage (get a mortgage loan)

You can also say:

• взять квартиру в ипотеку = to buy/get an apartment with a mortgage

So мы взяли её is a natural continuation referring to ипотека.

взяли is past tense plural of взять, which is perfective.

Perfective is used because this is a completed, one-time action: they made the decision and took out the mortgage.

The imperfective counterpart would be брали (from брать), which would suggest a repeated/ongoing process or background context.

свой/своя/своё/свои is a reflexive possessive meaning “one’s own,” and it refers back to the subject (мы).

• мы хотели свою квартиру = we wanted our own apartment (belonging to us)

нашу квартиру is also possible, but it often sounds more like you mean a specific apartment already identified as “ours” in the conversation. свою strongly emphasizes “our own (not rented / not someone else’s).”

It’s accusative because хотеть takes a direct object: “to want (what?)”.

• квартира (nominative) → квартиру (accusative)
• своя → свою (accusative feminine singular)

Russian word order is flexible, but this order is neutral and conversational:

• Ипотека кажется страшной, но мы взяли её... (contrast: scary, but we did it)
• ...потому что хотели свою квартиру (reason placed after the decision)

Other orders are possible for emphasis, e.g.:

• Потому что хотели свою квартиру, мы взяли её. (puts the reason first)

• ипотека: stress on the last а → ипотеКА
• её: stress on the second syllable → еЁ

In writing, you’ll often see её spelled as ее (without ё)—that’s common, but the pronunciation is still её.