AL chem 2008 幾個小問題

1.
transmittance is okay. the basis of these are basically the same.

2.
i can't think of good one. maybe it's sulfide titration..?
let's do it like this:
add known amount of excess sodium hydroxide to precipitate the Cu(II), followed by filtration. back-titrate the amount of hydroxide left with standard acid, thus amount of Cu(II) can be obtained.

and sulfate? use excess barium nitrate, filter the precipitate, dry and weigh.

3.
D is false: bromination destroys the aromaticity. notice it's naphthalene, not a di-ene.

then, see which carbocation is most stable.
all three are stabilized by aromatic ring, yet the carbocation center can be mono-substituted (A) or di-substituted (B&C). B&C are more stable owing to more electron-donating methyl groups on center.

finally, compare B & C for the electron density on the alkene. B has 2 methyl while C has one, thus B has higher electron density. [think about the nature of electrophilic addition]

B is most reactive.