I've never been good at chemistry, so I'm probably misremembering...

My understanding was that the cocaine's chemical structure is what reacts with the baking soda (and heat), leaving the adulterants to burn off. I guess unless they share the same property that binds the cocaine with the baking soda. The baking soda isn't meant to increase weight, there is an actual chemistry-based reason that it's used.

It's why people stopped "free-basing" cocaine once crack came around. "Free-base" is a chemistry term, and the reaction with the baking soda is what makes it no longer "free-base."

It weighs more because of the baking soda, but that's just like a substrate to deliver the cocaine, not an adulterant meant to make it weigh more.

Again, could be wrong and don't feel like looking it up because I don't really care about crack or cocaine