Unit 0 – Chemistry Review
Section 3 – Chemical Formulas
Molecular (Covalent) Compounds
1. What information can we tell about a compound given its empirical formula?
We can tell the smallest whole-number ratio of all the atoms in a given compound.
2. What additional information is conveyed when we know its molecular formula?
We can tell the mass of the molecule.
3. What additional information to we know when we see its structural formula?
We can tell what each atom is bonded to.
4. Two compounds have the same empirical formula; one is a gas at room temperature and the other is a liquid.
How is this possible? Just because they have the same empirical formula does not mean they are the same compound. Small changes
in atom arrangement and quantity can result in large differences in physical properties.
5. Determine the molecular and empirical formula of the following: Molecular first, then empirical.
a. The organic solvent benzene that has six carbon atoms and six hydrogen atoms C6H6 CH
b. The compound silicon tetrachloride, a substance used to make computer chips SiCl4 SiCl4
c. The reactive substance diborane, a compound with two boron atoms and six hydrogen atoms B2H6 BH3
d. The sugar glucose, a substance with six carbon, twelve hydrogen, and six oxygen atoms C6H12O6 CH2O
6. Write down the molecular and structural formulas represented by the following models:
C2H6O
C2H5OH
C2H5Br
C2H7N
CH3OH
PF3
Notice how some are written slightly different. The are all correct representations even though one is more condensed and one shows the valence
electrons.
Ionic Compounds
7. Which of the following compounds below likely represents an ionic compound and which represents a covalent
compound? Explain your answer.
The first one is likely an ionic compound because of the repeating pattern (of positive and negative ions).
8. Predict the charge of the most stable ion each element below is capable of forming:
a. Mg 2+
c. S 2e. F 1b. Al 3+
d. K 1+
f. O 2-
g. N 3h. Na 1+
9. Fill in the table for the compound made from each cation and anion pair. Use parentheses when necessary.
Cl
NO3
S2
CO32
N3
PO43
OH
Na+
NaCl
NaNO3
Na2S
Na2CO3
Na3N
Na3PO4
NaOH
NH4+
NH4Cl
NH4NO3
(NH4)2S
(NH4)2CO3
(NH4)3N
(NH4)3PO4
NH4OH
Sn2+
SnCl2
Sn(NO3)2
SnS
SnCO3
Sn3N2
Sn3(PO4)2
Sn(OH)2
Hg22+
Hg2Cl2
Hg2(NO3)2
Hg2S
Hg2CO3
(Hg2)3N2
(Hg2)3(PO4)2
Hg2(OH)2
Al3+
AlCl3
Al(NO3)3
Al3S2
Al2(CO3)3
AlN
AlPO4
Al(OH)3
Sn4+
SnCl4
Sn(NO3)4
SnS2
Sn(CO3)2
Sn3N4
Sn3(PO4)4
Sn(OH)4
NOTE: ONE of the above formulas is incorrect. If you can spot it, send me an e-mail. The first one to
find it and email me the answer will receive extra credit!
Naming Compounds: Molecular and Ionic
It is very important that you do as much of this as you can for memory. You will not be given the list on the AP test.
Show Formulas for the Following Compounds
calcium iodide CaI2
magnesium nitrate Mg3N2
iron (II) acetate Fe(CH3COOH)2
lead (IV) oxide PbO2
calcium hydride Ca(OH)2
copper (II) sulfide CuS
ammonium ion NH41+
hydrogen sulfide H2S
magnesium nitrate Mg(NO3)2
lead (IV) oxide PbO2
potassium chromate K2(CrO4)
cadmium (II) bromide CdBr2
copper (I) sulfide Cu2S
aluminum acetate Al(CH3COOH)3
antimony (V) sulfite Sb(SO3)2
vanadium (V) carbonate V2(CO3)5
nickel (II) sulfate NiSO4
arsenic (II) sulfite SbSO3
tin (II) fluoride SnF2
lead (IV) sulfide PbS2
hydrogen bromide HBr
lead (II) chlorate Pb(ClO3)2
manganese (II) oxalate MnC2O4
carbon tetrachloride CCl4
manganese (III) dichromate Mn2(Cr2O7)3
ammonium sulfate (NH4)2SO4
mercury (II) bisulfate Hg(HSO4)2
mercury (I) nitrite HgNO2
cobalt(II) hydroxide Co(OH)2
tin (IV) sulfide SnS2
lithium perchlorate LiClO4
manganese(III) permanganate Mn(MnO4)3
tetraphosphorus decoxide P4O10
silver cyanide AgCN
Show Names for the Following Compounds
KCN potassium cyanide
NaCl sodium chloride
SiH4 silicon tetrahydride
KSCN potassium thiosyanate
SO3 sulfur trioxide
AgIO silver hypoidodite
NO3- nitrate ion
HCN hydrogen cyanide
ZnO2 zinc peroxide
CuCl2 cupric chloride or copper (II) chloride
SF6 sulfur hexafluoride
KIO4 potassium periodate
CO carbon monoxide
CO2 carbon dioxide
(NH4)2C2O4 ammonium oxalate
Fe(HSO3)3 ferric bisulfate or iron (III) bisulfite
LiBrO lithium hypobromite
NO3 nitrogen trioxide
Hg2Cl2 mercurous chloride or mercury (I) chloride
MgCr2O7 magnesium dichromate
CuNO3 cuprous nitrate or copper (I) nitrate
CBr4 carbon tetrabromide
Show Names and Formulas for the Following Acids
hydrobromic acid HBr
HI hydroiodic acid
sulfurous acid H2SO3
HC2H3O2 acetic acid
chlorous acid HClO2
HF hydrofluoric acid
hydrochloric acid HCl
H3PO3 phosphorous acid
phosphoric acid H3PO4
HClO3 chloric acid
nitrous acid HNO2
H2CO3 carbonic acid
hydrofluoric acid HF
H2SO3 sulfurous acid
perchloric acid HClO4
HClO2 chlorous acid
Percent Composition and Empirical Formulas
10. A compound is 85.7% C and 14.3% H by mass. Determine its empirical formula. CH2
C:
85.7g 1 mol

 7.14 mol
1
12.011g
H:
14.3
1 mol

 14.19 mol
1 1.00794 g
11. In areas where temperatures get extremely cold, people must take special precautions to make sure machinery
runs properly. One compound contains 83% rubidium, 16% oxygen, and 1% hydrogen is used in low temperature
storage batteries. What is the empirical formula for this compound? RbOH
Rb :
83g
1 mol

 0.971 mol
1 85.4678 g
O:
16g
1 mol

 1.00 mol
1 15.9994 g
H:
1g
1 mol

 0.992 mol
1 1.00794 g
12. A form of phosphorus called red phosphorus is used in match heads. When 0.062 grams of red phosphorus burns
it combines with oxygen and 0.142 grams of product is formed. What is the empirical formula and name of this
substance? P2O5 diphosphorous pentoxide
P:
0.062 g
1 mol

 0.002 mol
1
30.974 g
O:
0.080 g
1 mol

 .005 mol
1
15.9994 g
13. A compound that is usually used as a fertilizer can also be used as a powerful explosive. The compound has the
composition, 35.00% nitrogen, 59.96% oxygen and the remainder being hydrogen. What is its empirical formula?
Given it is ionic, suggest a name for the compound. NO1.5H2  N2O3H4 (NH4)(NO3) ammonium nitrate
N:
35.00 g
1 mol

 2.50 mol
1
14.007 g
O:
59.96 g
1 mol

 3.75 mol
1
15.9994 g
H:
5.04 g 1 mol

 5.00 mol
1
1.0079
14. The common pain medicine, Advil, contains the active ingredient Ibuprofen that has a molar mass of about 184
g/mole. Ibuprofen contains 75.73% C, 8.74% H, the remainder being oxygen. What are the empirical and
molecular formulae for Ibuprofen? C6.5H9O1  C12H18O2 = 184 amu The empirical and molecular formula are
the same.
C:
75.73 g 1 mol

 6.31 mol
1
12.011g
H:
8.74g
1 mol

 8.67 mol
1
1.0079 g
O:
15.53g
1 mol

 0.97 mol
1
15.9994g
15. A compound is found to be 40% carbon, 6.7% hydrogen and 53.5% oxygen. Its molecular mass is 60 g/mol. What
is its molecular formula? CH2O = 30 amu. The molecular formula is C2H4O2
C:
40.0g 1 mol

 3.33 mol
1
12.011g
H:
6.7g 1 mol

 6.64 mol
1
1.0079g
O:
53.5 g
1 mol

 3.34 mol
1
15.9994 g
16. Epinephrine (adrenaline) is a hormone secreted into the bloodstream in 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 180 g/mol.
59.0 g 1 mol

 4.91 mol
1
12.011g
7.7 g 1 mol
N:

 0.55 mol
1
14.007g
C:
H:
7.1g 1 mol

 6.93 mol
1
1.0097g
O:
26.2g
1 mol

 1.64 mol
1
15.9994 g
C9H13O3N1 = 183 amu The empirical and molecular formula are the same.
Hydrates
17. When 5.00 g of FeCl3 · xH2O are heated, 2.00 g of H2O are driven off. Find the chemical formula and the name of
the hydrate.
H 2O :
2.00 g
1 mol

 0.111 mol
1
18.015 g
FeCl3•6H2O
FeCl3 :
iron (III) chloride hexahydrate
3.00 g
1 mol

 0.0185 mol
1
162.20 g
18. A 16.4 g sample of hydrated calcium sulfate is heated until all the water is driven off. The calcium sulfate that
remains has a mass of 13.0 g. Find the formula and the chemical name of the hydrate.
H 2O :
3.4 g
1 mol

 0.189 mol
1
18.015 g
CaSO4 • 2H2O
CaSO 4 :
13.0 g
1 mol

 0.095 mol
1
136.14 g
calcium sulfate dihydrate
19. A hydrate is determined to be 45.43% water and 54.57% CoCl2. What is the formula and name of this hydrate?
45.43 g
1 mol

 2.522 mol
100 g 18.015 g
54.57 g
1 mol
CoCl 2 :

 0.42 mol
100 g 129.93 g
H 2O :
CoCl2 • 7H2O
cobalt (II) chloride pentahydrate
20. What is the formula and name for a hydrate that is 90.7 g SrC2O4 (strontium oxylate) and 9.30 g H2O?
9.30 g
1 mol

 0.516 mol
100 g 18.015 g
90.7 g
1 mol
SrC 2 O 4 :

 0.516 mol
100 g 175.62 g
H 2O :
SrC2O4 • 1H2O
strontium oxylate monohydrate