This was written in 2014. Since then Apple iOS has created other workarounds for this problem, although the solution laid out here still works as well.
This is very different from nearly all of my other spiritual/philosophical blog posts. It's semi-complex, kinda techie, and intended to help make iPad use easier. So if you don't care about entering math or chemistry into an iPad, PLEASE IGNORE.
However, if you use an iPad and type chemical formulae or math equations on a regular basis, or other text that requires numerical subscripts or superscripts (such as H₂O or A² + B² = C²), this may be of interest to you.
Tonight I was talking with a colleague who teaches science about the fact that there is no ready-built, easy way to do subscripts or superscripts on an iPad. There are some third party apps, but nothing native to the system.
After doing some digging, I figured out a workaround. The problem centers around the fact that the sub/superscript numbers are not just normal numbers made small, but a separate kind of unicode text (in the same family as symbols such as © or ™). So, you have to train the iPad to input text that is NOT available on the keyboard.
However, it only takes about 10 minutes and the material in this blog, and you can train your iPad or iPhone to easily type sub/superscripts in any App (including Notes and iWork apps such as Pages and Keynote). Instructions and pictures are below:
1. Keep this blog open in your web-browsing app on your iPad / iPhone.
2. Switch to Settings --> General --> Shortcuts (see picture above)
3. Open "Add new shortcut" at the bottom of pane (see picture above)
4. In the "Phrase" box, cut and paste one of the sub- or superscript characters in the list below (such as Subscript Zero ₀).
5. In the "Shortcut" box, type the text you will enter in your keyboard to make it produce the subscript. I chose 0! and 1! and 2! (etc.) for the subscripts. I chose 0$ and 1$ and 2$ (etc.) for the superscripts.
6. Once you have entered all of your shortcuts, you will be able to type them in any app and produce sub/superscripts. One word of warning: You must put a SPACE before the shortcut phrase to make it recognize it.
So, if you enter H2!O you will NOT get H₂O.
But, if you enter H 2! O you WILL get H ₂ O.
Or, if you enter A 2$ + B 2$ = C 2$ you WILL get A ² + B ² = C ²
The only downside I have found is that if you really care about formatting, you will have to go back and delete the spaces in between. Hope this helps someone out there!