Have you ever wondered why they are
pronounced differently? This is why.
Kansas was named for
the Kansa, a Siouan tribe that lived in the region. The Kansa
people were called, in plural, Kansas, and that became the name
of the state.
Arkansas was named for a related Siouan tribe, the Quapaw. The
Algonquians called them “akansa,” joining their own a- prefix
(used in front of ethnic groups) to the Kansa name. It took some
time for Arkansans to come to agreement on pronunciation. In
1881, a heated disagreement between the state's two senators,
one who said “arKANzis” and the other who said “ARkansaw,” led
to a ruling by the state legislature making the “ARkansaw”
pronunciation official.