Drawing up a chemical formula app for iPhone and iPad

The program is designed to help improve understanding and memorization of chemistry and its formulas. The user can create formulas by typing them in the appropriate field, select their complexity, and add a favorite. The user can also redefine the list of all added formulas, the favorite formulas will be highlighted in yellow. 
After creating several formulas, the user is able to use the find-in test mode. On this screen, he sees a mixed formula, and he needs to add a formula using mixed symbols.