1 mole contains the same number of particles as there are in 12g of carbon-12 atoms by definition. This number is called Avogadro's number or Avogadro's constant (NA) and is equal to 6.022 x 1023 particles.
1 mole of a pure substance has a mass in grams equal to its molecular mass (MM) [also known as molecular weight (MW) or formula mass (FM) or formula weight (FW)]. This is often referred to as the molar mass.
1 mole of an ideal gas has a volume of:
22.4 litres (22.4L) at S.T.P. [Standard Temperature and Pressure, 0oC (273K) and 101.3kPa (1 atm)]
24.47 litres (24.47L) at S.L.C [Standard Laboratory Conditions, 25oC (298K) and 101.3kPa (1atm)]
Examples
Avogadro's Number (NA)
1 mole of atoms or molecules contains 6.022 x 1023 atoms or molecules
eg, 1 mole of helium atoms (He) contains 6.022 x 1023 helium atoms (He)
To find the number of atoms in a known number of moles,
multiply the moles by 6.022 x 1023 eg, 2 moles of helium atoms (He) contains 2 x 6.022 x 1023 = 1.2044 x 1024 helium atoms. (He)
To find the moles of atoms,
divide the number of atoms by 6.022 x 1023 eg, If we have 4.2154 x 1023 neon atoms, how many moles of neon atoms are there?
Moles of neon atoms = (4.2154 x 1023) ÷ (6.022 x 1023)
= 0.7 mol
1 mole of molecules contains 6.022 x 1023 molecules.
eg, 1 mole of oxygen molecules (O2) contains 6.022 x 1023 oxygen molecules (O2).
To find the moles of molecules,
multiply the number of molecules by 6.022 x 1023 eg, ½ mole of oxygen molecules (O2) contains ½ x 6.022 x 1023 = 3.011 x 1023 oxygen molecules (O2).
To find the number of molecules,
divide the moles of molecules by 6.022 x 1023 eg, If we have 6.022 x 1021 chlorine molecules (Cl2), how many moles of chlorine molecules are there?
Moles of chlorine molecules = (6.022 x 1021) ÷ (6.022 x 1023)
= 0.01 mol
1 mole of molecules does not necessarily contain 1 mole of atoms of each element in the formula
eg, 1 mole of HCl WILL contain 1 mole of hydrogen atoms (H) and 1 mole of chlorine atoms (Cl)
eg, 1 mole of HCl contains 6.022 x 1023 hydrogen atoms and 6.022 x 1023 chlorine atoms
eg, 5 moles of oxygen molecules (O2) contains 5 x 2 = 10 moles of oxygen atoms (O)
eg, 5 moles of oxygen molecules contains 10 x 6.022 x 1023 = 6.022 x 1024 oxygen atoms.
eg, 1 mole of ammonia molecules (NH3) will contain 1 mole of nitrogen atoms (N) and 3 moles of hydrogen atoms (H)
1 mole of ammonia molecules contains 6.022 x 1023 nitrogen atoms and 3 x 6.022 x 1023 = 1.8066 x 1024 hydrogen atoms
Molar Mass
1 mole of a pure substance has a mass in grams equal to its molecular mass (MM).
eg, 1 mole of Helium (a monatomic gas with the formula He) has a mass equal to its relative atomic mass, 4.003g
eg, 1 mole of hydrogen gas (a diatomic gas with the formula H2) has a mass equal to 2 x 1.008 = 2.016g
eg, 1 mole of ammonia gas (NH3) has a mass equal to 14.01 + (3 x 1.008) = 17.034g
eg, 1 mole of water (H2O) has a mass equal to (2 x 1.008) + 16.00 = 18.016g
Ideal Gas Volumes
at S.T.P [0oC (273K), 101.3kPa (1 atm)], an ideal gas has a volume of 22.4L
To find the volume of a certain number of moles of gas, multiply the moles by 22.4L
eg, What is the volume of 2.5 moles of chlorine gas at S.T.P?
Volume of chlorine gas = 2.5 x 22.4 = 56.0L
To find the moles of a certain volume of gas, divide the volume by 22.4L
eg, How many moles of argon are in 3.36L of argon gas at S.T.P?
moles of argon gas = 3.36 ÷ 22.4 = 0.15 mol
at S.L.C [25oC (298K), 101.3kPa (1 atm)], an ideal gas has a volume of 24.47L
eg, To find the volume of a certain number of moles of gas, multiply the moles by 24.47L
What is the volume of 0.2 moles of hydrogen sulfide gas at S.L.C?
Volume of hydrogen sulfide gas = 0.2 x 24.47 = 4.894L
To find the moles of a certain volume of gas, divide the volume by 24.47L
eg, How many moles of carbon monoxide are in 70.5L of carbon monoxide gas at S.L.C?
moles of argon gas = 70.5 ÷ 24.47 = 2.881 mol
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