It really depends on your school. At my school, AP chem is a double period, the teachers attempt to give their students more homework than any other chem student in the nation, there's a 100% exam pass rate, and you can get a C in the class and still get a 5 on the exam. I have a friend in California, who got straight A's, yet his whole class would get 1's and 2's on the exam. Calling a course "AP" doesn't always identify its rigor.
But if you go to a very competitive, nationally ranked school such as mine, B's are good! They will look at you in the context of your school. Also, senior year grades aren't given as much attention as your other high school grades.