M.Sc Chemistry at IIT Kharagpur is a five-year integrated MSc course offered by the Department of chemistry. 

In the first year, all the courses will be the same for all the departments. Out of these courses, only one is chemistry. Other courses are from other departments like Electrical, computer science, Mechanical, Physics, etc. Here, you are given a chance to explore at least one course from most of the departments. Based on your performance in first year (i.e CGPA) you can change your department (also called Depc). But for this, you need to get a CGPA of more than the cut-off CGPA of the department to which you want to change. 

For instance suppose, Electrical Engineering department has a cut-off CGPA of 9.2 for DepC then you need to get a CGPA of more than 9.2 for DepC to Electrical. 

From the second year most of the courses will be from your department. Though, there will be a few courses from other departments as well. So, yes you will be studying mostly Chemistry from the second year onward. you can look at the complete Curricula Subjects List here