Have you ever thought about what your hands and forearms are actually doing at the moment of impact? If not, please give this a try because it's one of the most important parts of the swing.
Try to get into the impact position, like you are about to make solid contact with the ball. Now flip your trailing wrist like you were casting a fishing pole. This is referred to as a wrist break, and it's not a move that you want to make in golf. So if you are trying to "flip" your hands through the ball at impact, this tip may help you understand the correct way to make this happen.
If you put a wrist watch on you'll be able to visualize the correct moves to make. As your leading arm approaches impact the watch face should be getting close to pointing exactly down the target line, or to the flag. Now simply ROTATE the watch face so it's pointed at the ground. With a club in your hands, you'll see that this move makes your trailing wrist and forearm "flip" on top of your leading wrist and forearm.
You also see that this will help to "close" the face of your club nicely, that will both reduce your slice, and add distance. This is the correct move to be completing through impact.
It's important to note that your forearms should be working together as well. Try to keep your forearms as close to each other as possible through the impact zone. If you can master this move, you'll find increased distance and it will also do wonders for your slice.