Hi camille, I'm an alto and when I did your exercise on chest belting the one with the phrase "that's mine" I stopped singing in chest register and switched to mix when i hit the note C5 ..not only with that exercise I mean its almost every time I try belting I stop belting at that note... what should I do to make it better? 

Hi, Manar! That's perfectly normal, and it's the healthier option. Ideally, you'll start mixing in that range (between A4 and C5) anyways. The ideal (for belt style) is a healthy mix that still sounds "chesty" and strong.