1) There is a problem I have noticed with students using hydroxide. Instead of correctly writing Ca(OH)2 for calcium hydroxide, many want to write CaOH2.
That's wrong. Learn what the ChemTeam thinks is the reason.
2) There are many polyatomic ions which are not mentioned in the ChemTeam tutorials. Superoxide is one of them. Superoxide is O2¯. For example, here is the formula for potassium superoxide:
KO2
Be aware that the formula IS NOT potassium peroxide, but superoxide.
This particular compound happens to have use in a "re-breathing" apparatus, used in underwater diving. This device does not release bubbles into the surrounding water, as does SCUBA gear. The KO2 helps to absorb the additional CO2 in exhaled air, allowing it (with some oxygen added) to be "re-breathed" instead of releasing the exhaled air into the water, as SCUBA does.
This has obvious military applications.