Broken white piece

The part you are showing us is known as a tilt latch. To be able to properly identify it, we need to see an undamaged version of it removed from the window. I'd especially like to see its underside so I can see what kind of locking tooth we are working with. 

I also want to express a little confusion about the description information about its function. When you say spring, are you referring to a balance? The tilt latch does not interact with the function of the balance in any way. Could we have you clarify on what you are describing to us please?