A sample of impure NaHCO3 with an initial mass of 0.654 g yielded a solid residue (consisting of Na2CO3 and other solids) with a final mass of 0.456 g. Determine the mass percent of NaHCO3 in the sample.

15. which of the following is not human-caused groundwater pollution? a. water in an aquifer dissolves elements such as arsenic and mercury from surrounding rock. b. water in an aquifer is contaminated by leachate that seeps into the ground from a landfill. c. water in an aquifer becomes polluted with chemicals used in hydraulic fracturing, or fracking. d. water in an aquifer absorbs harmful bacteria from the drainage field of a septic tank.