Question #5c383

Grams and milliliters measure two completely different physical quantities.

The gram (#"g"#) is a unit of mass, so the #100# #"g"# indicates the mass of that particular water sample.

The milliliter (#"mL"#) is a unit of volume, so the #100# #"mL"# indicates the volume of that particular water sample.

#" "#

What we cam do with this information, if we want, is calculate the density of the water, using the formula

#"density" = "mass"/"volume"#

So

#color(red)("density") = (100color(white)(l)"g")/(100color(white)(l)"mL") = color(red)(ul(1color(white)(l)"g/mL"#

Look familiar?

Volume can be accurately measured from fundamental units of length, but it's use for accurate substance measurements is hindered by the variation in density (mass/volume) of all substances.

Measuring 100 grams will always give you 100 grams. ( Weight is also different, and relates to the gravitational field that the mass is measured in). Measuring 100mL of water will result in a different volume whenever the ambient temperature changes.

ALL compounds (even atoms) can be measured by mass - solid, liquids and gases. Liquids and gases can be more easily measured by volumes, but special care needs to be taken to account for the measurement conditions. For the best accuracy and precision, all measurements and calculations are done on a MASS basis whenever possible.