Worksheet 1: REPRESENTATIVE PARTICLES
Directions: For each substance below, state the representative particle. If the RP
is a molecule, state the number of atoms that make up the molecule. If the RP is
a formula unit, state the number of ions that make up the formula unit.
1. NaCl
_________________________________________
2. H2SO4
_________________________________________
3. K+
_________________________________________
4. CaCl2
_________________________________________
5. S
_________________________________________
6. S6
_________________________________________
7. NH4Br
_________________________________________
8. Ca3(PO4)2 _________________________________________
9. C6H12O11
_________________________________________
10. Mg(NO3)2 _________________________________________
11. Cl2
_________________________________________
12. KMnO3
_________________________________________
13. H2O2
_________________________________________
14. H3PO3
_________________________________________
15. NH4+
_________________________________________
16. Fe2O3
_________________________________________
17. NaC2H3O2 _________________________________________
18. PO43-
_______________________________________
19. Hg
_________________________________________
20. O2-
_________________________________________
Worksheet 2: THE MOLE AND AVOGADRO’S NUMBER
One mole of a substance contains Avogadro’s Number (6.02 X 1023) of molecules. How many molecules are in the quantities below?
1. 2.0 moles
2. 1.5 moles
3. 0.75 mole
4. 15 moles
5. 0.35 mole
How many moles are in the number of molecules below?
1. 6.02 x 1023
2. 1.204 x 1024
3. 1.5 x 1020
4. 3.4 x 1026
5. 7.5 x 1019
Worksheet 3: MOLAR MASS
Determine the molar mass (the mass of one mole) of each compound below. Remember to
include units (either amu or g/mol).
Hint: for hydrated compounds such as CuSO4•5H2O, add the molar mass of the salt (CuSO4) to
the mass of the number of water molecules indicated by the coefficient (5H2O = 5 water
molecules).
1. KMnO4
________________________________________
2. KCl
________________________________________
3. Na2SO4
________________________________________
4. Ca(NO3)2
________________________________________
5. Al2(SO4)3
________________________________________
6. (NH4)3PO4
________________________________________
7. CuSO4•5H2O
________________________________________
8. Mg3(PO4)2
________________________________________
9. Zn(C2H3O2)2•2H2O ________________________________________
10. Zn3(PO4)2•4H2O
________________________________________
11. H2CO3
________________________________________
12. Hg2Cr2O7
________________________________________
13. Ba(ClO3)2
________________________________________
14. Fe2(SO3)3
________________________________________
15. NH4C2H3O2
________________________________________
Worksheet 4: PERCENTAGE COMPOSITION
Determine the percentage composition of each of the compounds below.
Answers:
Work:
1. KMnO4
K = __________
Mn = __________
O = __________
__________________________________________________________________
2. HCl
H = __________
Cl = __________
__________________________________________________________________
3. Mg(NO3)2
Mg = __________
N = __________
O = __________
__________________________________________________________________
4. (NH4)3PO4
N = __________
H = __________
P = __________
O = __________
__________________________________________________________________
5. Al2(SO4)3
Al = __________
S = __________
O = __________
__________________________________________________________________
Solve the following problems.
6. How many grams of oxygen can be produced from the decomposition of
100 g of KClO3? __________
7. How much iron can be recovered from 25.0 g Fe2O3? __________
8. How much silver can be recovered from 125 g of Ag2S? __________
Worksheet 5: Determining Empirical Formulas
What is the empirical formula (lowest whole number ratio) of the compounds below?
1. 75% carbon, 25% hydrogen
ANSWER:
2. 52.5% potassium, 47.3% chlorine
ANSWER:
3. 22.1% aluminum, 25.4% phosphorus, 52.5% oxygen
ANSWER:
4. 13% magnesium, 87% bromine
ANSWER:
5. 32.4% sodium, 22.5% sulfur, 45.1% oxygen
ANSWER:
6. 25.3% copper, 12.9% sulfur, 25.7% oxygen, 36.1% water
ANSWER:
Worksheet 5 continues onto the next page…
Worksheet 5 Continued: Determining Molecular Formulas (True Formulas)
1. The empirical formula of a compound is NO2. Its molecular mass is 92.0 g/mol. What is its
molecular formula?
ANSWER:
2. The empirical formula of a compound is CH2. Its molecular mass is
molecular formula?
70 g/mol. What is its
ANSWER:
3. A compound is found to be 40.0% carbon, 6.7% hydrogen and 53.5% oxygen. Its molecular
mass is 60. g/mol. What is its molecular formula?
ANSWER:
4. A compound is 64.9% carbon, 13.5% hydrogen and 21.6% oxygen. Its molecular mass is 74
g/mol. What is its molecular formula?
ANSWER:
5. A compound is 54.5% carbon, 9.1% hydrogen and 36.4% oxygen. Its molecular mass is 88
g/mol. What is its molecular formula?
ANSWER:
Worksheet 6: COMPOSITION OF HYDRATES
A hydrate is an ionic compound with water molecules loosely bonded to its crystal structure. The water is in a
specific ratio to each formula unit of the salt. For example, the formula Na2S•9H2O indicates that there are nine
water molecules for every one formula unit of Na2S. Answer the questions below.
1. What percentage of water found in Na2S•9H2O?
2. A 5.0 g sample of a hydrate of BaCl2 was heated, and only 4.3 g of the anhydrous
salt remained. What percentage of water was in the hydrate?
3. A 2.5 g sample of a hydrate of Ca(NO3)2 was heated, and only 1.7 g of the
anhydrous salt remained. What percentage of water was in the hydrate?
4. A 3.0 g sample of Na2CO3•H2O is heated to constant mass. How much anhydrous
salt remains?
5. A 5.0 g sample of Cu(NO3)2•nH2O is heated, and 3.9 g of the anhydrous salt
remains. What is the value of n?
Worksheet 7: Chemical Quantities Review (CP)
1. Name the representative particle for the following substances:
♦ N ______________________
♦ CO2 _________________________________
♦ N+ ______________________
♦ C6H6 _________________________________
♦ N2 ______________________
♦ Na2SO4____________________
♦ NaHCO3___________________
♦
NaOH ________________________
2. Calculate the molar mass of each the following substances:
♦ C6 H6
__________________________________
♦ Ca(NO3)2 __________________________________
♦ MgSO4•7H2O
___________________________
3. How many moles are in 20.1 g of HC2H3O2?
4. Calculate the mass of 15.6 moles of CuSO4•5H2O.
5. How many molecules are in 100.5 g N2O?
6. Calculate the volume of 67.8 g of Cl2 gas at STP.
7. How many oxygen atoms are in 6.50 molecules of HC7H5O2?
8. Calculate the mass of 2.35 x 1015 molecules of CH4.
9. Calculate the percentage composition of Ca(OH)2.
10. How many grams of zinc could be extracted from 1.00 kg (1000 g) of ZnCl2?
HELPFUL TIPS FOR THE UPCOMING TEST
! Know the four representative particles and be able to determine what the
R.P. is for a given substance.
! Know how to find the molar mass / molecular weight (MW) of a given
substance.
! Know how to determine the number of atoms / ions present in one
molecule or formula unit of a given substance.
! Know how to convert between units of mass, moles, volume,
representative particles, and atoms or ions when appropriate.
! Know the values of standard temperature and pressure.
! Know how to calculate percent composition.
! Know how to calculate the mass of some part of a compound that could
be recovered.
o For example, a typical bottle of fingernail polish contains 215.25 mg
of tin (IV) oxide. What mass of tin is present in this amount?
!
!
!
!
!
!
!
!
!
!
!
!
Begin calculations with the given value.
PAY ATTENTION TO UNITS
Convert to the mole before converting to any other unit.
Round to the tenth’s place when calculating molar mass.
Attach the appropriate units to all values.
Give your answer with the same number of significant digits as the given
value when converting between units.
PAY ATTENTION TO UNITS
Use Avogadro’s number (6.02 x 1023 representative particles / mole) to
convert to and from representative particles.
Use molar mass to convert to and from mass.
Use molar volume (22.4 L / mole) to convert to and from volume of a gas
at STP.
PAY ATTENTION TO UNITS
Remember that density = mass (g) / volume (L)
Remember: 1 mole = 6.02 x 1023 R.P.’s
1 mole = molar mass in grams
1 mole = 22.4 L of gas @STP