Just base your calculations on a factor of 60221 and add zeros in the string:
str_cat_num(Moles, "%.0f0000000000000000000 mole(s) of gas", n);
\
Thanks! @JustSid, wow, I hadn't even considered the possibility of making my own special data type. I'd have to use a struct for that right? I'll go with Superku's suggestion