That seems a bit confused. On IP address2 you should simply type the following to do the mount - the / and IP address2 you have aren't meaningful unless you're mounting on a secondary IP of the host which I gather you aren't.
Code:
mount -t nfs -o rw {IP address1}:/ /mnt_for_70
On IP address2 you simply type the following to unmount it:
Unmounting a filesystem doesn't do anything to its contents. You should be able to remount it again after you unmount it. (This is also true of device filesystems - if you don't destroy or reformat the underlying device the data is still there - it simply isn't visible until mounted.)