Strong & Weak Acids and Bases
A strong acid and a strong base will neutralize to reach an equivalence point of 7.
A strong acid and a weak base will neutralize to reach an equivalence point below 7, because the strong acid will ionize completely to form H+ ions while the weak base will not dissociate fully.
Hydrochloric acid is a strong acid.
Sodium carbonate is a strong base.
Thus, they will reach an equivalence point of 7.
On the other hand, sodium bicarbonate is a weak base.
Thus, it will react with HCl to reach an equivalence point below 7.