1. When he comes back, I will go out with him.
2. If he comes back, I will go out with him.
(What is the difference between the two sentences?)
3. I don't know when he will come back.
4. Because he will come back, I will go back home.
5. If he comes back, I will go back home.
6. I don't know the time when he will come back.
(Are the sentences all correct?)
For the first two sentences --
Using "when" assumes he is definitely coming back.
Using "if" express doubt whether he'll be back or not.
The others are correct.