How can I tell if this is baking soda or powder? Sure it'd be easier and cheap to just buy new soda and powder but I'm curious. 

I had a jar of either baking soda or powder. The marker with which I'd labeled it rubbed off during a house move and I do not recall which one it was. 

Is there an easy way to test if I have a jar of baking powder or soda?
Baking powder contains starch, which is insoluble.

Baking soda is completely soluble

Take a small bowl, and put 1/8 tsp of the substance in the bottom.

Add water.

If the substance is bicarbonate of soda, the solution will be completely clear.

If it is baking powder, a cloudy/powdery residue will remain.

(You can also use excess vinegar which gives the same result, and fizzes in a pleasingly sciencey fashion...)