Mole Calculations

Mole Calculations

Volume, cm3 Mass, g Moles Atomsuse density use

molar massuse

Avogadro’snumber

gcm3

mol g

atoms molx x x

A graduated cylinder holds 25.4 cm3 of mercury. If the density of mercuryat 25 oC is 13.534 g / cm3, how many moles of mercury are in the cylinder?How many atoms of mercury are there?

HINT: Volume of solids/liquids and moles are not directly connected. You must first use the density to convert the volume to a mass, and then derive the quantity of mercury, in moles, from the mass. Finally, the number of atoms is obtained from the number of moles.

Kotz & Treichel, Chemistry & Chemical Reactivity, 3rd Edition , 1996, page 93

Therefore, the volume of mercury is found to be equivalent to 344 g of mercury.

Volume, cm3 Mass, g Moles Atomsuse density use

molar massuse

Avogadro’snumber

gcm3

mol g

atoms molx x x

. 13.534 g Hg 1 cm3 Hg

25.4 cm3 Hg = 344 g Hg

Knowing the mass, you can now find the quantity in moles.

. 1 mol Hg . 200.6 g Hg

344 g Hg = 1.71 mol Hg

Finally, because you know the relation between atoms and moles (Avogodro’snumber), you can now find the number of atoms in the sample.

. 6.02 x 1023 atoms Hg . 1 mol Hg

1.71 mol Hg = 1.03 x 1024 atoms Hg

A

A B C

B

C

Kotz & Treichel, Chemistry & Chemical Reactivity, 3rd Edition , 1996, page 93

Formation of Ammonia