I believe the reason could be your ages. He's older, so he gets money to go out and such.

Do you ever ask for anything? Perhaps if you did, and then pointed out all the good you do around the house, you may get something you request.

Now if you have already talked to your mom and she flipped, did you explain all this to her? Maybe try and tell her you feel unappreciated with what you do. She may feel that as the kid, it is your responsibility to help around the house. Which it is, but I can still see why you are upset that your brother does nothing and everything.

I believe that all parents try to treat their kids the same, but it's impossible.. I mean you're different people, different ages ect.. I think that maybe at 13 she buys you things? Maybe you don't feel like she gives you the same because you get other things, and he gets the money.
I think that helping out around the house doesn't mean you're entitled to money ect.. When I was 13 I used to have to help clean the house ect, and I got £3 pocket money on a really good week, if I was lucky. So it shouldn't be expected..
Also there may be things your brother does that you dont notice, or nips to the shops ect for your mum?
When you're 16 you will probably get the same as he gets now, you just dont see it as fair, because you're seeing him get it now x