It's generally not recommended to store baking soda directly next to spices in your pantry due to its odor-absorbing properties. Baking soda can absorb the aromas of nearby spices, potentially affecting their flavor and the baking soda's effectiveness.
Baking soda (sodium bicarbonate) is a powerful deodorizer and readily absorbs odors from its surroundings. While this is beneficial for keeping your refrigerator fresh, it's not ideal in a pantry where spices are stored. Spices contain volatile aromatic compounds that give them their distinct flavors. If baking soda is placed too close, it can absorb these compounds, diminishing the potency and altering the intended flavor profile of your spices. Furthermore, the baking soda itself might become subtly flavored by the spices, which could be undesirable depending on its intended use in baking. To prevent this, store baking soda in an airtight container, away from spices and other strong-smelling items. A separate shelf or area in the pantry is preferable.
To test the freshness of your baking soda, pour a small amount of vinegar into a bowl and add a spoonful of baking soda. If it fizzes vigorously, it's still active. If not, it's time to replace it, regardless of where it was stored.