Question

to make sure that the white powder was all sodium chloride and not mixed with sodium hydrogen carbonate, would you add a little less or a little more hydrochloric acid to the reaction?

Answer 1

NaHCO₃+HCl$\to$ NaCl+H₂O+CO₂(gas)

If bubbles of the gas (carbon dioxide) intensely evolve during the reaction, then the sample is containing NaHCO₃