Helpful Chemistry links: 

BHS Chemistry Team's Reference Google Site -- https://sites.google.com/bisd303.org/bhschemistry/home -- links to all the learning objectives as well as videos on the main topics within each unit

http://www.chem.purdue.edu/gchelp/  --> nice visual reference for general chemistry with several practice items

http://www.simbucket.com/welcome-to-simbucket/ --> Select "chemthink" from the list on the main page to get lots of helpful tutorials and simulations in general chemistry

http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/chemcon.html#c1 --> more advanced tutorial than Purdue's but several are still applicable for high school level chemistry. 

https://www.khanacademy.org/science/chemistry --> series of good videos to help students understand and walk through processes. 

http://antoine.frostburg.edu/chem/senese/101/tutorials/  --> first-semester chem tutorials with quizzes and slides.