Is it normal that my mom always mad at me?

Maybe, she's going through menopause?

I'm sorry your mom's such a bitch.. hopefully you don't have to live with her.

My mom's the same. Some people are just horrendous bitches and don't care enough to realize it or try to change.

Maybe you're a horrible person and don't realise it?

Year-round PMS? XD

Bi polar? Just an option she may just be an angry woman

I always ask her why she's angry? She always says because I don't respect her , I think that respect is give and take thing,
I respect her buy she doesn't.
Btw I'm 19 and my mom is 50.

Have you asked her why she's angry? Communicate with her and tell her how you feel, maybe that'll fix the problem.

If I had this problem today I would tell my mom,
"Mom, I hope you will tone those abusive tirades back a little or I'm going to be tempted to record some of them and play them for the counselors at Child Protective Services and try to get you some help with your anger issues. Deliberate infliction of emotional cruelty can be an ugly rap.
Or maybe I could post the audio to YouTube and send the link to your siblings and the grandparents.
I am your child. I remember a time when I loved you very much. Please don't persist in trying to suffocate what's left of that feeling."

Perhaps she is angry at other things going on in her life, and she's taking all of her anger out on you guys.

I realize that it sucks - my grandmother is the same way. What I do to avoid it all is I just stay in my room or I'm not at home (my room is in the basement).

Perhaps you could try to avoid her more to avoid problems or maybe if you don't want to try to avoid her have you considered talking to her? Trying to discuss what's bothering her?