Using 'scrat' name in a web app Is there any problem that I may have in the future if I use the name 'scrat' in an web app for App Store? For example 'Scrat Store' or something similar? 

Since the name 'scrat' is the name of an Ice Age character and obviously is trademarked.
If it's a trademarked name then you will have a problem.  It might get through the app review process the first and second time but eventually, the trademark owner, in this case, 20th Century Fox, will find out and and ask/tell you to remove it (or go to Apple to have it removed).