1. How many moles are in 3.4 x 10²⁴ molecules of HCl?
if there are 6.022 × 10²³ molecules in 1 mole of HCl
then there are 3.4 × 10²⁴ molecules in X moles of HCl
X = (3.4 x 10²⁴ × 1) / 6.022 × 10²³ = 5.6 moles of HCl
2. How many grams are in 2.59 x 10²³ formula units of Al₂O₃?
if there are 6.022 × 10²³ units in 1 mole of Al₂O₃
then there are 2.59 × 10²³ units in X moles of Al₂O₃
X = (2.59 x 10²³ × 1) / 6.022 × 10²³ = 0.43 moles of Al₂O₃
number of moles = mass / molecular weight
mass = number of moles × molecular weight
mass of Al₂O₃ = 0.43 × 102 = 43.86 g
3. How many grams are in 9.05 x 1023 atoms of silicon?
if there are 6.022 × 10²³ atoms in 1 mole of silicon
then there are 9.05 × 10²³ atoms in X moles of silicon
X = (9.05 x 10²³ × 1) / 6.022 × 10²³ = 1.5 moles of silicon
mass = number of moles × molecular weight
mass of silicon = 1.5 × 28 = 42 g
4. If you had 7.00 moles of PtO₂, how many grams would you have?
mass = number of moles × molecular weight
mass of PtO₂ = 7 × 227 = 1589 g
5. How many moles are in 29.2 L of oxygen gas at STP?
At standard temperature and pressure (STP) we may use the following formula:
number of moles = volume (L) / 22.4 (L / mol)
number of moles of oxygen = 29.2 / 22.4 = 1.3
6. What is the volume (liters) of 75.8 g of N₂ at STP?
number of moles = mass / molecular weight
number of moles of N₂ = 75.8 / 28 = 2.7 moles
At standard temperature and pressure (STP) we may use the following formula:
number of moles = volume (L) / 22.4 (L / mol)
volume = number of moles × 22.4
volume of N₂ = 2.7 × 22.4 = 60.48 L
