• Batch size that chemists measure out for any substance is 6.02*1023. This is the Avogadro constant, NA. This is the mole. It is defined as the amount of substance containing 6.02*1023 particles.
• The number of moles of a substance is given symbol n.
Why the number?
• Avogadro’s number s the number of carbon atoms in 12 g of pure carbon-12. Thus, if you measure 1.0 g of hydrogen, you have 1 mole of hydrogen atoms, if 16.0 g of oxygen, you have 1 mole of oxygen atoms, if 18.0g of water, you have 1 mole of water molecules.
• The relative mass of a substance tells us the mass of 1 mole of that substance.
Relating number of moles to number of particles:
• n(X)=(number of particles of X)/(6.02*1023)
o Where X is the type of particle being measured. This can be transposed to:
o Number of particles of X = n(X) * (6.02*1023)0042
Particles in ‘packages’
• E.g. “how many carbon atoms are present in 5 mol of sucrose, C12H22O11?” or “How many moles of hydrogen atoms are present in 3*1021 water molecules?’
• How many carbon atoms are present in 5 mol of sucrose, C12H22O11
o Each molecule contains 12 carbon atoms.
o Calculate the number of sucrose molecules present:
• Number of C12H22O11 molecules = n(C12H22O11 molecules) * 6.02 * 1023
o Calculate the total number of carbon atoms:
• =12 * number of C12H22O11 molecules
• =3.6*1025 atoms
• How many atoms are present all together?
o The molecule contains 45 atoms altogether.
o Again, we multiply the number of moles by Avogadro’s number to find the number of molecules. WE then multiply this by 45 to find the total number of atoms.
• How many moles of carbon atoms are present?
o There are 5 moles of the molecule, and there are 12 carbon atoms per molecule. This means the number of moles of carbon is 12 * the number of mols of sucrose.
o Therefore, the answer is 60.
Calculations the second:
• Calculate the number of moles of Cl- ions...