yĭ jing - already -(已经) yĭ qián- before - (以前) I'm pretty sure that both of the first characters here is the 3rd tone. U know characters r just for writting while the tones r for listening and speaking. In chinese there'r so many different characters have the same syllable and tone. But let them alone, not so much care about that. Learn Pinyin well first.

Tones do NOT affect the way the character is written. The character represents MEANING. That is why you have two different characters there. I think you need a new book.

The tone does not effect the character. The character is a representation of meaning. A lot of words in Chinese sound the same but have different meanings and there are characters that have the same tone mark, same pinyin but the character is not the same and of course has a different meaning. yi qian 一前 for before. There isn't a 'g' at the end. yi(3) jing(1) 已经 (there should be a tone mark for the second character)

There are many homonyms in Chinese. There are even words with two sounds and intonation, which are identical sounding - which have different meanings (the source of jokes). There are words which are written the same, but pronounced differently depending upon the context. There are even phrases now which are now hip, which are due to common typing errors: 神马都是浮云

Yĭjing - already-已经 Yĭqiáng- before －以前 if you write these characters one by one and depends on pinyin,of course you will feel confused. Usually,people will write a sentence,then they will not confused. So I suggest you remember a character through by a short sentence.