Probably not, but it won't be good for the dog, either.
three and a half ounces
5.509 tablespoons.
4
A couple tablespoons of baking soda will do the trick, for sure.
2
6 tablespoons.
No.
About a tablespoon per half a cup of water. Baking soda works well for stains and odor which all dentures, retainers, mouth guards or expanders will have from wearing. Be sure to brush any mouth piece/denture first with a toothbrush so the baking soda can do a better job. If one tablespoon isn't strong enough increase the baking soda to two tablespoons. It's best to let them soak overnight.
The proper substitution for baking powder is half baking soda and half cream of tartar. They both have leavening properties. If you don't have cream of tartar available, I guess I would go toward 2/3 - 3/4 baking soda and the rest cornstarch.
Don't use that stuff.
Make a paste of baking soda and water, and soak the sea shells in that overnight. The baking soda won't hurt the shells at all. Make sure you use baking SODA and NOT baking POWDER.
That amount of baking soda would be enough for 16oz of water, so cut it in half.