How to calculate the density of a substance at standard temperature and pressure

Question

How to calculate the density of a substance at standard temperature and pressure

Answer 1

This is actually pretty easy. Lets use the example of a small rock or pebble.

First, we get our direction from the equation for Density.

Density = Mass / Volume

What this means is we need two values: Mass (in grams) and Volume (in cm3)

so to tackle the mass problem, we simply weight the rock / pebble on an electronic balance. Lets say it weights 50 grams.

To get the volume, is a bit more tricky. First, we pour a carefully measured amount of water in a beaker or test tube. So lets say we measure out 250 ml (which is equal to 250 cm3).

Then We place the rock in this beaker or test tube. The CHANGE in volume, is the volume of the rock itself. so if you put the rock in the test tube / beaker and the new volume reads say 270 ml, then the volume of this rock is 270 - 250 = 20 ml.

So now we have both values, and its just a simple calculation

Density = Mass / Volume = 50 / 20 = 2.5 grams per cm3

Hope that helps :-)