Sumi Akagi

Sorry, I'm a bit of a newbie when it comes to tris HCL buffer, but I have some questions: I'm trying to make a tris HCL buffer of 1.2M with 10.5 pH. My preferred volume is 7.5 mL, and I know the amount of tris base (1.09g ) and HCl (3uLwith HCL being 37.2%(12.1M) )I need, but I don't know the amount of deionized water I need to dissolve the tris base in. Is it possible to use a recipe for 1L and add 800mL of deionized water or does that change the outcome for the tris HCL buffer?