The AP Chemistry course on KA can be used to prepare for the AP Chemistry Exam, which is administered by the College Board and is used to gain university credits in many countries, but is most common in the United States (where it is based) and Canada. It likely won't be of much help to prepare for the national exams you mentioned, and those exams don't have preparation resources available on Khan Academy. 

You could use Khan Academy to brush up on certain topics that you think are on your exams, but Khan Academy doesn't have specific resources for the national exams you listed.