Aren't older siblings...

Aren't older siblings supposed to be more responsible then the younger sibling?
I washed the dishes yesterday, and it wasn't even my turn. It was my older sisters'. I done them on my own free will. Nobody told to do them. It was Cora's turn to wash them, but I knew that she was busy doing nothing,  that she would never get them done, and that they don't get cleaned all the way when she washes them. I washed the dishes before myself. The last time, my mom had me put some aside for Cora b/c she didn't get all of her dishes done. She didn't do them. I haven't gotten a "Thank you for washing Cora's/my dishes for her/me." It would be nice if someone did thank me...