Sahin, Chemistry is a tricky subject to score in although many deem it to be one of their favorites. Now, moving over to your query, if your exam is done, then you cannot change anything and thinking about the marks or the chances of passing would not do any good, rather focus on other subjects so that you can compensate for "not-so good" chemistry exam. As regarding grace marks or what some technically refer to as normalization, it is very difficult to predict if there would be grace marks given, although most of the authorities have a policy of normalization of marks in case of marks being very close to passing marks, so you should hope for the same. However, you should not predict anything until the results are out as you never know the examiner's thought- process while checking your answers, so all you can do is to hope for the best and prepare for other exams.

Good Luck.