You should throw out baking soda after it's expiration date or when it becomes stale as after it's expiration date or when it becomes stale the baking soda loses it's potency and power and the baked goods won't turn out as good and it won't work as good as fresh baking soda.
Baking soda does expire although it won't harm you if you do use it for baking with or cooking with or for use for whitening teeth etc.
However baking soda loses it's effectiveness in baking when it is expired so the baked goods won't turn out as good.
When unopened baking soda is shelf stable until it's best by date on the box which is around 2 years.
After you open the box of baking soda it should be used within 6 months as it starts to lose it's power and potency although it remains safe to use.
You can use baking powder in baking if you don't have baking soda.
When using baking powder in place of baking soda when you don't have baking soda you just use 3 times as much of baking powder to replace baking soda with.
For example if a recipe calls for one teaspoon of baking soda, you instead would use three teaspoons of baking powder.
And since baking powder contains a little salt you should also halve the salt the recipe calls for.
Baking soda and baking powder are not the same although they can be used in place of one another in recipes.
Sodium bicarbonate and bicarbonate of soda are other names for baking soda.
Baking powder is made of baking soda plus cream of tartar and cornstarch.
Just remember that baking soda is stronger than baking powder, so you'll want to use a quarter of the amount of baking soda as powder.
So if the recipe calls for 1 tsp. baking powder, use ΒΌ tsp. baking soda.