Я купил два литра сока и литр молока, потому что завтра к нам придут гости.

Купил is the perfective past form of купить, so it presents the action as completed: the speaker bought the juice and milk, and that action is finished.

Покупал would be the imperfective past form and would focus more on the process, repetition, or background context. In this sentence, the point is the completed result, so купил is the natural choice.

Also, купил shows that the speaker is male. A female speaker would say купила.

This is because Russian number phrases affect the form of the noun:

• два литра = two liters
• один литр is usually shortened here to just литр = one liter

After 2, 3, 4, the noun usually goes in the genitive singular, so:

• два литра
• три литра
• четыре литра

After 1, the noun is nominative singular:

• один литр

So in this sentence:

• два литра сока
• литр молока = understood as один литр молока

Because after a measure word like литр, Russian normally uses the genitive for the substance being measured.

So:

• литр сока = a liter of juice
• литр молока = a liter of milk

And since the first measure word is part of a number phrase:

• два литра сока = two liters of juice

This is similar to English a liter of juice, where juice depends on liter. In Russian, that dependency is shown through the genitive case.

Because the preposition к takes the dative case.

The pronoun мы changes like this:

• nominative: мы = we
• genitive/accusative: нас
• dative: нам

So:

• к нам = to us / to our place

In this sentence, к нам придут гости means guests will come to us or more naturally guests will come over to our place.

Because the action happens tomorrow: завтра.

Придут is the future tense of the perfective verb прийти and means will come / will arrive.

This fits well because the sentence refers to a single completed future event: the guests will come over tomorrow.

If you used an imperfective future, it would sound different in meaning and would focus less naturally on the completed arrival.

Придут comes from прийти, which literally means to come on foot, but in many everyday contexts Russian uses it more generally for coming/arriving, especially when the exact method of travel is not important.

So к нам придут гости is a very normal way to say guests are coming over to us.

If you specifically wanted to say they are coming by vehicle, you could use приедут. But here придут is the standard neutral choice.

Because потому что introduces a subordinate clause meaning because.

The sentence has two parts:

• Я купил два литра сока и литр молока
• потому что завтра к нам придут гости

In Russian, clauses like this are normally separated by a comma, so the comma before потому что is required.

Russian word order is much more flexible than English word order. The sentence could be rearranged in several ways and still be grammatical.

For example, you could also say:

• ...потому что завтра гости придут к нам.
• ...потому что к нам завтра придут гости.

The version завтра к нам придут гости sounds natural and puts the flow roughly like this:

1. tomorrow
2. to us
3. will come
4. guests

This can make гости feel like the new or important information at the end.

That is normal in Russian. Unlike English, Russian often places the subject after the verb, especially when introducing an event or presenting new information.

So:

• гости придут = the guests will come
• придут гости = also the guests will come, often with a slightly more natural information flow in context

Both are grammatical, but the second one is very common in sentences like this.

Russian has no articles, so гости can mean either guests or the guests, depending on context.

In this sentence, English would naturally often say guests are coming over tomorrow, but the guests are coming over tomorrow could also fit in a different context.

Russian leaves that distinction to context rather than using words like the or a.

Because Russian often expresses that idea differently.

In English, come over suggests coming to someone’s home. In Russian, this is naturally conveyed by:

• к нам = to us / to our place
• придут = will come

So к нам придут гости already includes the idea of guests are coming over.

Russian does not need a separate word matching English over here.

Yes. Russian allows that.

For example:

• Потому что завтра к нам придут гости, я купил два литра сока и литр молока.

This is grammatical, but it may sound a little more marked or explanatory depending on context. The original order is more neutral.

So both are possible, but:

• Я купил..., потому что... = very natural, straightforward
• Потому что..., я купил... = also correct, but with different emphasis

Russian past tense does not require a specific time expression like today or yesterday. If the speaker says Я купил, it simply means I bought.

The timing is understood from context: the person bought these things already, and the reason is that guests are coming tomorrow.

So the timeline is:

• buying: already completed
• guests arriving: tomorrow

That contrast between past and future is perfectly normal in Russian.