While preparing chloroalkane from primary and secondary alcohols by the action of halogen acids, anhydrous ZnCl2 is used.

In pradeep's its work is written as co-ordination with oxygen atom and breaking of C-O bond. Whereas in another book, it says that it removes water.

So are the both reasons same thing? If yes, why? And what is meant by co-ordination anyway, does it mean that it makes bond with O atom?

both statements mean the same thing.

ZnCl2 is a lewis acid. OH of alcohol gives it lone pair to ZnCl2 ad gets coordinated(coordination means forming bond by donating or accepting lone pairs). looks like this:

R---O⁺----(ZnCl2)^- assume H is attched to O(as not able to draw the bond here; charges appear as oxygen loses e^-s and Zn

                                                                  accepts e^-s.)

now one Cl attacks at R (i.e C--O bonds break)and bonding electrons remain with O to remove + sign. (NOTICE THAT SOME HCL(acid) IS ALSO ADDED IN RXN;and Cl comes from HCl) now further in presence of H⁺ H2O and ZnCl2 separate out.

please approve by clicking "YES" below