Why do they bother to wipe the area where the lethal injection iv is going to be placed with alcohol?
The Master has already covered this one.
Cecil’s answer notwithstanding, the main reason for why a vein stands out after rubbing with a swab is not because of the effect of the alcohol. It’s because of local inflammatory effects caused by the rubbing action.
You can test this for yourself. Just run a thumbnail firmly down the inside of your forearm, and almost immediately a reddened weal pops up. The underlying cause is the release of histamines and other inflammatory substances that act on the local tissue to cause vasodilation of the capillaries therein; hence the red colour.
The same effect is achieved by vigorously rubbing a vein with a swab prior to precisely identifying a spot to insert the IV cannula. The other common method is to slap the general area to achieve the same result. Both are tricks that have been used in the trade for as long as IV’s have been administered.