Why is it called "bicarbonate"?
From Wikipedia


  The prefix bi in bicarbonate comes from an outdated naming system and is based on the observation that there is twice as much carbonate ($\ce{CO3}$) per sodium in sodium bicarbonate ($\ce{NaHCO3}$) as there is in sodium carbonate ($\ce{Na2CO3}$).


The IUPAC name for it agrees with its chemical formula: sodium hydrogen carbonate.