How to pacify an angry mom?

I'd say it depends on what you've done. And what your mother is like!

Apologising is always a good first step. Explaining why you did what you did helps. If she is really angry a little sacrifice like doing something nice for her you wouldn't normally do (e.g. tidying up the house for her) or buying her a little treat (e.g. chocolates) can help to pacify her a little.

It all depends on what she is upset about.
I am a mother and if I am upset about something, first of all I need to be able to vent about it and the recipient of the venting needs to be patient with me. When I am finished venting, then I will calm down. The recipient should also remain calm and then that will help me to calm down. Do not try to sweet talk me, just be patient with me.
Hopefully that method will work with your mom too.

For me, you always need to say sorry and listen to your mum on what she's saying to you. When she starts nagging, just keep quite, don't say a word just wait until she calms down and explain to her.
Happy myloting.