Topic 9
Name __________________________________
Review: The Mole
Students will be able to:
1. State that one mole = 6.02x1023
2. Convert moles
number of particles*
Key:
3. Calculate the molar mass of a compound
All
Most Some
4. Convert moles
grams
5. Convert mass
number of particles*
6. Calculate the percentage composition of the elements of a compound when given the
compound’s formula.
7. Work out the empirical formula of a compound from mass data.
8. Work out the empirical formula of a compound from percentage composition data.
9. Work out the molecular formula of a compound when given molar mass and the empirical
formula.
10. Work out the empirical formula and then the molecular formula of a compound when given
mass/percentage composition data and molar mass.
11. Use percentage composition as a conversion factor
Note: a strong grasp of scientific notation, significant figures and dimensional analysis is also required.
1. State that one mole = 6.02x1023
One mole of a substance contains Avogadro’s number of particles of that
substance. State Avogadro’s number.
Did you get it right? If so, proceed to the next objective. If not, get some help (notes,
book, peer, teacher, etc) and then try the additional question below:
How many atoms in a mole of atoms?
2. Convert moles
number of particles
How many atoms in 4.2 mol of iron?
How many moles in 1.2x1024 molecules of carbon
dioxide?
Did you get them right? If so, proceed to the next objective. If not, get some help (notes, book, peer, teacher, etc) and then
try the additional questions below:
How many atoms in 2.8 mol of neon?
*
Atoms, molecules or formula units
How many moles in 3.1x1022 molecules of water?
3. Calculate the molar mass of a compound
Calculate the molar mass of ammonium sulphide.
Did you get it right? If so, proceed to the next objective. If not, get some help (notes, book, peer, teacher, etc) and then try
the additional question below:
Calculate the molar mass of magnesium sulphate (MgSO4).
4. Convert moles
grams
How many moles in 230.g of silver nitrate?
What is the mass of 0.25 mol of sodium chloride?
Did you get them right? If so, proceed to the next objective. If not, get some help (notes, book, peer, teacher, etc) and then
try the additional questions below:
How many moles in 2.0g of carbon dioxide?
What is the mass of 5.66 mol of calcium
carbonate?
5. Convert mass
number of particles
How many molecules in 23g of boron trichloride? What is the mass of 7.3x1025 fluorine molecules
(F2)?
Did you get them right? If so, proceed to the next objective. If not, get some help (notes, book, peer, teacher, etc) and then
try the additional questions below:
How many molecules in 2.0g of carbon
monoxide?
†
What is the mass of 6.8x1022 formula units† of
potassium chloride?
Formula units are the representative particles of ionic compounds.
6. Calculate the percentage composition of the elements of a compound when given the
compound’s formula.
What is the percentage composition of Cr2O3? (1dp)
Did you get it right? If so, proceed to the next objective. If not, get some help (notes, book, peer, teacher, etc) and then try
the additional question below:
What is the percentage composition of CaCl2? (1dp)
7. Work out the empirical formula of a compound from mass data.
Work out the empirical formula of a molecule containing 3.12g lithium, 2.72g carbon, and 10.83g
oxygen.
Did you get it right? If so, proceed to the next objective. If not, get some help (notes, book, peer, teacher, etc) and then try
the additional question below:
Work out the empirical formula of a compound that contains 2.27g of carbon, 3.6g of fluorine and
20.1g chlorine.
8. Work out the empirical formula of a compound from percentage composition data.
Work out the empirical formula of a compound that is 40.0% carbon, 6.7% hydrogen and 53.3%
oxygen by mass.
Did you get it right? If so, proceed to the next objective. If not, get some help (notes, book, peer, teacher, etc) and then try
the additional question below:
Work out the empirical formula of a compound that is 72.2% magnesium and 27.8% nitrogen by
mass.
9. Work out the molecular formula of a compound when given molar mass and the
empirical formula.
Work out the molecular formula of ethylene glycol (it’s found in antifreeze). The molar mass is
62g/mol and the empirical formula is CH3O.
Did you get it right? If so, proceed to the next objective. If not, get some help (notes, book, peer, teacher, etc) and then try
the additional question below:
Work out the molecular formula of a compound with empirical formula P2O5 . The molar mass is
283.9g/mol.
10. Work out the empirical formula and then the molecular formula of a compound when
given mass/percentage composition data and molar mass.
Methyl butanoate smells like apples. Its percentage composition is 58.8% carbon, 9.8% hydrogen and
31.4% oxygen. Its molar mass is 102 g/mol. Work out its empirical and molecular formulae.
Did you get it right? If so, proceed to the next objective. If not, get some help (notes, book, peer, teacher, etc) and then try
the additional question below:
Nicotine is 74.1% carbon, 8.6% hydrogen, 17.3% nitrogen by mass. Its molar mass is 160 g/mol.
Work out its empirical and molecular formulae.
11. Use percentage composition as a conversion factor
Work out the mass of aluminium in 200.0 g of aluminium cyanide, Al(CN)3
Did you get it right? If so, proceed to the next objective. If not, get some help (notes, book, peer, teacher, etc) and then try
the additional question below:
Work out the mass of hydrogen in 151g of sodium hydride, NaH
Extension:
1) In the USA, the 23rd of October is known as “Mole Day”. Can you think of a reason why?
2) A compound contains hydrogen, carbon and oxygen atoms in the ratio 6:2:1. What is the empirical
formula of a compound?
3) Fertilisers often contain NH4NO3.
a. State the name of the compound.
b. Calculate the molar mass of the compound.
c. Calculate the percentage composition of nitrogen in the compound.
d. Calculate the number of oxygen atoms in 31g of NH4NO3.
4) Epinephrine is a hormone secreted into the bloodstream at times of danger and stress. It is 59.0%
carbon, 7.1% hydrogen, 26.2% oxygen and 7.7% nitrogen by mass. Its molar mass is about 183
g/mol. Work out its molecular formula. (You will need to round a fair bit)
5) Calcium chloride is used to absorb household humidity. Water molecules become attached to each
calcium chloride formula unit, forming a complex called a hydrate.
a. State the formula of calcium chloride.
b. Mary has found out that the calcium chloride hydrate contains 0.018 mol of water for every
0.0091 mol of calcium chloride. How many water molecules are attached to each calcium
chloride formula unit?
c. Explain why the term formula unit has been used, rather than molecule.
------------------------------------------------------------------------------------------------------------------------------------Answers: (remember your answers might be off by a hundredth or so, depending on which periodic table you’ve used)
1) 6.02x1023; 6.02x1023. 2) 2.5x1024atoms; 2.0mol; 1.7x1024atoms; 0.051mol. 3) 68.16g/mol; 120.37g/mol. 4) 1.35mol; 15g; 0.045mol;
567g. 5) 1.2x1023; 4 600g; 4.3x1022; 8.4g. 6) 68.4% Cr and 31.6% O; 36.1% Ca and 63.9% Cl. 7) Li2CO3; CFCl3. 8) CH2O; Mg3N2. 9) C2H6O2;
P4O10. 10) Empirical: C5H10O2, Molecular: C5H10O2; Empirical: C5H7N, Molecular: C10H14N2. 11) 51.37g; 6.35g.
Extension: 1) the date is 10/23. 2) H6C2O. 3)a) ammonium nitrate; b) 80.06g/mol; c) 35.00% d)7.0x1023 ; 4) C9H13O3N; 5)a) CaCl2;
b) about 2; c) calcium chloride is an ionic compound and ionic compounds are not made up of molecules because they are giant structures.