It's pretty big for a scraper and doesn't really look like the flint adzes I've seen from Missouri. (Many of them are thicker than that.)
I'd call it a biface.
You see that curvature on pieces for a couple of reasons, the most common is that it was just made on a thinner spall of chert that had some curve to it. They maximized the length and ended up with a slightly bent piece. It could also be that it's a preform and they were going to do something with the base. You often see an bottom edge that is going to be flaked (fluted, notched, etc.) angled with an edge below the plane of the middle of the blade. Beveled for lack of a better term. Here are two pictures of a fluted point base from my collection that shows it. (I don't think the original relic here was going to be a fluted point, but maybe notched like a Smith or something.)