Weighing Moles

What it shows

If the molar mass of a substance is found using the periodic table, a mole of the substance can be weighed out in grams.

How it works

The molar mass is the number of grams in one mole of a substance. For any pure substance, you can use its chemical formula and the periodic table to calculate its molar mass. Then weigh out that number of grams, and you have one mole of the substance! For example, the molar mass of carbon dioxide, CO₂, is 12.01 g/mol + (2*16.00 g/mol) = 44.01 g/mol. If we place 44.01 g of CO₂ in an evacuated container, that will be one mole of CO₂.

Setting it up

The electronic scales are set up in front of a camera or under a doc cam. In a secondary container, there is a cube of lead weighing 208 g. In addition, there are 18 g of water in a bottle with an empty bottle for the tare weight, and 200.6 g of mercury in a bottle with an empty bottle for the tare weight.

Ask students how they would measure out one mole of lead. Hopefully they come up with 207.2 grams from the periodic table. Ask similar questions for water and mercury.