Quote Originally Posted by Звездочёт
In modern Russian the unstessed "о" are pronounced like "a". So the word "чистой" are pronounced like "чистай".
The unstressed "o" is pronounced like "a" only when it stands directly before the stressed syllable in a word. In other cases it's pronounced like "schwa".

"O" is pronounced like "a": товарищ, погода, непорядок, корова, молоко.

"O" is pronounced like "schwa": много, мало, удостоверение, молоко.