This is for industrial chem but i think the NaCl electrolysis is the hardest to understand at first. Followed by the ionic/cationic/anion detergent shit, but it's pretty easy to get your head around them under 30 minutes.
I also used to have trouble with these sort of questions... 2 important formulae to remember: q = mctriangle(T) and triangle(H) = q/n
And obviously u need the need to know the basic formulae such as n = cv, n = m/M and c1v1 = c2v2. Also, u MUST know how to rearrange these formulae... VERY IMPORTANT!