Breakdown of На уроке орфографии мы проверяем правописание трудных слов в словаре.
в
in
мы
we
слово
the word
на
in
Questions & Answers about На уроке орфографии мы проверяем правописание трудных слов в словаре.
Why is it на уроке, not на урок?
Because на уроке uses the prepositional case after на to mean at/in the lesson or during the lesson.
- на уроке = at the lesson, in class
- на урок = to the lesson
So here there is no movement; it describes where the action happens.
Why is it орфографии?
Орфографии is in the genitive singular because it depends on урок:
- урок орфографии = a spelling lesson / a lesson in orthography
This is a very common Russian pattern:
- урок математики = a math lesson
- урок музыки = a music lesson
- урок русского языка = a Russian lesson
So in на уроке орфографии, only уроке changes because of на; орфографии stays genitive because it means lesson of spelling.
What case is правописание here?