Я вымыла палитру после урока, чтобы краски не засохли.

I

Breakdown of Я вымыла палитру после урока, чтобы краски не засохли.

• не: not
• чтобы: in order to
• после: after

Questions & Answers about Я вымыла палитру после урока, чтобы краски не засохли.

Why is it вымыла, not мыла?

Because вымыла is the perfective past tense of вымыть, meaning washed completely / cleaned off.

Here the speaker is talking about a completed action: the palette got washed after the lesson.
If you said мыла, that would be the imperfective verb, which focuses more on the process: was washing / used to wash / washed without emphasizing completion.

So in this sentence, вымыла fits better because the result matters: the palette was cleaned so the paints would not dry out.

Why does вымыла end in -а?

In the past tense, Russian verbs agree with gender and number.

• вымыл = masculine
• вымыла = feminine
• вымыло = neuter
• вымыли = plural

So Я вымыла tells us the speaker is female.
If the speaker were male, it would be Я вымыл палитру...

Why is it палитру, not палитра?