End of year examples

[@#035;3]

a) This question is essentially asking to find the mol of oxalic acid excess in 100ml of the original solution.
To find the mol of oxalic acid excess we must first find the mol of I3- (n=cv)
then using stoichiometry, n(oxalic acid in 20ml)=n(I3-)
then n(oxalic acid in 100ml)=n(oxalic acid in 20ml)*5/1

which gave me an answer of 0.00560 mol or 5.60*10^-3

b) This question is asking the mol of oxalic acid reacting with MnO2..
This is a back titration, so the mol of oxalic acid that reacted with MnO2
---> n(oxalic acid initially) - n(oxalic acid excess).

which gave me an answer of 0.00940 mol or 9.40*10^-3 mol

c) Here use stoichiometry to find the mol of MnO2. Then simply find the mass by
mass=mol*molar mass, then the percentage

which gave me an answer of 65.3%.

Hopefully i was helpful.

[blacksanta62]

You were of great help. I used the top equation, could you explain why the bottom one should be used? Thank you

[blacksanta62]

If I feel like I'm particularly weak in naming hydrocarbons, what would you recommend I do? Do you have any tips that could help me name them? Or videos? Or notes? I now have the head start lecture notes but haven't read them yet. I'm pretty sure that hydrocarbons don't come up in great detail until chapter 9 or so in the Heinemann 2 book so I want a bit of an understanding so I can pick it up a lot quicker later on.