Ask about graduate student life and the quality of life in the local town or city. Inquire also about the financial situation, particularly the availability of research stipends, of teaching assistantships and summer funding. In chemistry, at least, every reputable university should provide some sort of financial aid. There are numerous reasons for being rejected from a particular graduate program, many of them out of your control, such as retirement or departure of the most appropriate potential advisor, or the shortage of funds to support graduate students. Increase your odds by sending out more than one application, although don't lower your standards so much that you end up enrolling in a weak program just because you were accepted there.
Graduate schools consider a variety of factors in selecting students.
What is most important is evidence of independent research, especially a successful senior project. Your application essay should highlight what you have done outside of the classroom. Although nobody really expects an undergraduate to be able to propose a specific PhD thesis topic, you should define your general interests and demonstrate your familiarity with current problems in the field. A prospective advisor will be most concerned about your interest in, commitment to, and potential in his or her field. The best way to give your letter and application substance, then, is to have done something in the field as an undergraduate.