It is used as a production agent for PVC and a stimulant for oil production in rock formations.
Along with zinc amalgam, this substance acts as the catalyst in the Clemmensen reduction, and it reacts with all metals except for mercury and the coinage metals.  It is used as a production agent for PVC and a stimulant for oil production in rock formations. This substance is commonly used as a neutralizing agent of sodium hydroxide during titrations, producing water and sodium chloride as a result. For 10 points, identify this acid that also makes up the majority of the gastric juices found in the human stomach.
Along with zinc amalgam, this substance acts as the catalyst in the Clemmensen reduction, and it reacts with all metals except for mercury and the coinage metals.  
hydrochloric acid [accept hydrogen chloride before the word acid; accept HCl]