The antacid is basic so it neutralizes acidity or lowers it. Then if it goes into the esophagus, it's not as strong and it doesn't hurt, and it also calms your stomach because the acidity in your stomach is also lower. Antacids are therefore taken by many people, especially as they grow older and things like heartburn become more common.
Density is a physical property derived from mass devided by volume (first part of the question)
m=v*p (p is rho)
m=9.5*60 =570 g
Density of water is 1g/cm^3 (centimeter cubed)