Baking powder can dissolve in water or not?
Yes, because it is a Sodium salt, all of those are soluble!
Baking powder is Sodium Bicarbonate a polar compound that is particularly amenable to water (a polar solvent). So Baking powder will dissolve faster than a non-polar powder like Talcum powder. Also baking power is very finely ground and will present a large surface area to the water which hastens dissolving. Salt in comparison although a strongly polar compound is course ground and will take longer to dissolve.
Baking powder is not the same as baking soda. Baking powder is a 1:3 ratio of baking soda to cream of tartar, which are both raising agents designed for different purposes - one of them is activated by water, the other by heat. Baking soda is "strong" compared to baking powder, and is not a direct substitute for baking powder.
For a good long time if it is kept properly stored. Here is a test you can use to make sure your baking powder is usable . Put water in a teaspoon and sprinkle a little bit of the baking powder in the water. If your baking powder is good the water will fizz sort of like a soda does. if you don't hear or see the fizz then baking powder is no good and…