What are some common mistakes students make with polyatomic compounds?
In my own experience being a grade eleven chemistry student in a grade twelve chem class, there are several minor mistakes that myself and my peers make with polyatomic compounds.
Really, the only thing that trips A LOT of people up is the charges on each of the polyatomic ions and remembering to cross charges to determine formulae.
For example, if I was to say... Write the equation for the reaction between Potassium and the Phosphate ion... you should begin by determining that Potassium has a charge of 1+ and Phosphate has a charge of 3-. To determine this formula, you cross these charges over and they become the subscripts in the formula...
K (charge of 1) + PO4 (charge of 3-) --> K3PO4
Hope this helps!