1. When he comes back, I will go out with him.

Question

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?)

Answer 1

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.