Originally Posted by piepatch
Soda and baking powder come with a date on them, but I always put an "opened" date on them with a marker. They generally have a long shelf life, especially soda, but in your case, I would toss them to be sure.
When it's past the 'good for cooking' date, use it for cleaning.
Dip a wet finger in the soda and scrub spots on dishes. Works great on tea rings, baked on spots on glassware, etc. Best of all it doesn't scratch!