Why are both mass and volume often measured in chemistry investigations?
Because different substances have different densities. For example, if you knew a reaction produced a gas, you could work out what volume this would be, and you could design your apparatus to prevent any pressure build-up. Also, sometimes it is easier to measure liquids by volume in a measuring cylinder or pipette than it would be to put them on a weighing machine. For example, some liquids are unstable when exposed to air, and so it is easiest to measure them by syringe.