[Christine1]

Is it possible to separate or isolate 1,4,7-heptanetriol and 1,3,7-heptanetriol from each other?
Also, is it possible to selectively carry out hydration on alkene that has same number of hydrogens attached, for instance, (RCH=CHR)?

Thank you so much 

[rucik5]

They probably have similar boiling points and polarities, so can't distill or do a column (can't be sure until you do a GC and TLC though). You might be able to form an acetal from 1,3- hydroxyls (1,4 - 4,7 - 3,7 would form a 7 or 8 membered ring with i.e. acetone) from the second triol. What I have in mind (not those exact conditions):

Link: http://www.organic-chemistry.org/protectivegroups/carbonyl/dioxanes-dioxolanes.htm

I don't think you can easily differentiate between two alkenes which have the same substitution, unless there is a large steric or electronic factor which might change the outcome of the reaction.