Silver dollars and half dollars are often collected for more than their silver value, cleaning them will only ruin their collectable value. You will never add value to a coin by cleaning it (the exception being coins dug out of the ground) and can possibly shave tens, hundreds or even thousands of dollars off the value of your coin by cleaning it.
Never.
Rubbing it gently with sodium bicarbonate.
It is tarnished, but not ruined. Clean/polish it as you would with a polishing cloth, or bring it to a jeweler. It will be fine.
Mix salt and vinigear, and soak it in. But if its valubale, DO NOT USE TOO MUCH SALT.
It happens with exposure to air and certain chemicals. The silver atoms combine with oxygen to form a layer of silver oxide, which is what causes the discoloration.See the Related Links for "How to clean and polish silver" to the bottom for the answer.
Tarnished silver jewellery can be cleaned by wrapping it in aluminum foil, then placing it in a bicarbonate of soda solution.
You don't.
http://home.howstuffworks.com/how-to-clean-furnishings3.htm
no
Can you? Yes. Should you? Probably not - you'll remove toning (which many collectors like) and likely scratch the coin's surface.
you use baking powder and coke
Use windex and a coffe filter liner thing to wipe it off and it should be gone...
One suggestion is Lemon or Lemon rinds