Would sodium bicarbonate absorb moisture from air and become a cake? Many
solids do that. Not sure if sodium bicarbonate would also.
Yes, I think it would with time and humidity. Sodium bicarbonate in its box
is often put into refrigerators to absorb smells. To be regenerated requires
heat. But to do so would release CO2 and convert sodium bicarbonate to
2NaHCO3 -> Na2CO3 + CO2 + H2O
So most people just throw away the box when it becomes stale.