Will chemical burn leave scar?

Possibly: The depth of a burn determines whether a scar will be left, no matter what the cause. A shallow burn will not leave a scar but the skin color will be changed. Deeper burns cause proportionately more severe scarring.

Less if washed off: There are many varied chemicals that can burn but the key point is to immediately wash off the area with a large amount of cold water. One wants to prevent the chemical from being absorbed and causing more tissue damage. Cold constricts the tissue so that less is absorbed as well as having the water dilute the chemical.