Chemistry
Name:__________________
Period: ____
Formation of Compounds
Packet 7
Day
In Class Work
1
2
3
4
5
6
7
8
9
Lab
Lab
Periodic Table of Elements
Ionization
Nomenclature
Writing Formulas
Writing Chemical Compound Names
Naming
Naming and Molar mass
Outcomes
 The students will be able define ion, ionization potential, valence electron, cation, and anion.
 Students will comprehend the relationship of columns from the periodic table to ion charges
and number of valence electrons.
 Students will be able to explain why ionization potential decrease as one goes down a column
and increase as one goes across the row.
 Given electron configuration students will predict ionization potential.
 Students will identify metals, transition metals, non-metals, and noble gases.
 Students will write the formula for any binary compound and vice versa.
 Given the formulas and charges for polyatomic ions, the students will write the formula for any
ternary compound and vice versa.
1
DETERMINATION OF AN EMPIRICAL FORMULA
INTRODUCTION:
In this experiment, you will determine the empirical formula of a compound. In so doing you will gain a clear
understanding of the difference between an empirical formula and a molecular formula.
An empirical formula gives the simplest whole number ratio of the different atoms in a compound. The
empirical formula does not necessarily indicate the exact number of atoms in a single molecule. This
information is given by the molecular formula. For certain compounds, the empirical formula and the molecular
formula are the same; for other compounds the empirical and molecular formulas are different. In all cases, the
molecular formula is a simple multiple of the empirical formula. Consider the following examples.
Experiments have shown that any sample of pure water contains two atoms of hydrogen for every atom of
oxygen. The empirical formula for water is, therefore, H2O. Various molecular formulas; H2O, H4O2, H6O3,
and so on, are possible. Each of these formulas expresses the same ratio of hydrogen and oxygen atoms as is
expressed in the empirical formula. Scientists have shown, however, that each water molecule actually consists
of two atoms of hydrogen bound to one atom of oxygen. Therefore, the molecular formula for this compound is
H2O. For water, the empirical and molecular formulas are identical.
For other compounds, the empirical and molecular formulas are different. Consider hydrogen peroxide. This
compound contains one atom of hydrogen for each atom of oxygen, and its empirical formula is HO. There is,
however, no stable molecule having this formula. In fact, it has been shown that individual hydrogen peroxide
molecules contain two atoms of hydrogen and two atoms of oxygen. The molecular formula of this compound
is, therefore, H2O2.
In some cases, two or more different compounds share the same empirical formula. This is true of acetylene and
benzene. Each of these compounds has the empirical formula CH. The molecular formula of acetylene,
however, is C2H2, while that of benzene is C6H6.
In this experiment, you will determine the empirical formula of magnesium oxide, a compound that is formed
when magnesium metal reacts with oxygen gas. In determining this empirical formula, you will make use of the
law of conservation of mass.
According to this law, the total mass of the products of a chemical reaction must equal the total mass of the
reactants.
mass of Mg + mass of O2 = mass of MgxOy
Therefore, knowing the mass of magnesium used and the mass of magnesium oxide produced in this reaction,
you can determine the mass of oxygen used. This ratio between the number of moles of magnesium used and the
number of moles of oxygen consumed can then be calculated and the empirical formula of magnesium oxide can
be written on the basis of this ratio.
SAFETY:
The smoke given off, and the extreme heat must be contained safely. Safety goggles must be worn at all times,
and a face shield might be added if available.
Handle the crucible only with the tongs. There is a significant burn hazard associated with the handling of
crucibles because a hot crucible looks exactly like a cold crucible.
Remove the gas burner from beneath the crucible before using the crucible tongs to remove the crucible and its
lid. Use the tongs to grasp the lid by its porcelain knob; the crucible should be grasped by its edge.
2
PROCEDURE:
DAY – 1
1. Place the crucible on a clay triangle balanced on a ring support clamped to a ring stand. Light the gas burner
and adjust it to give a clear blue flame (A yellow flame will deposit soot on the crucible and cause a large error
in your data.). Place the burner under the crucible. Adjust the height of the ring support so that the bottom of the
crucible is in the hottest part of the flame. Place the crucible lid slightly ajar on the crucible (The crucible lid
should be large enough to fit loosely down over the crucible edge.).
2. Heat the crucible so that its bottom glows red for five minutes. Remove the burner and allow the crucible and
crucible lid to cool. This will take at least 10 minutes. CAUTION: The crucible gets extremely hot. Never touch
it. Always use crucible tongs in handling this piece of equipment. When the crucible and lid are completely
cool, use crucible tongs to transfer them to a balance. Do not place a hot crucible on the balance. Inaccurate
mass readings and damage to the balance may result. Determine the mass of the empty crucible and lid to the
nearest 0.01 g. Record this mass in the DATA TABLE.
3. Coil a 25-cm length of magnesium ribbon and place it in the bottom of the crucible. Determine the combined
mass of the crucible, lid, and the magnesium. Record this mass in the DATA TABLE.
4. CAUTION: Do not look directly at the burning magnesium. The intense light may hurt your eyes. View
Place the crucible, without its lid, on the clay triangle. Heat the crucible strongly until the magnesium ignites.
CAUTION: Be careful to keep the crucible at arm's length at all times. Do not inhale the "smoke" produced.
When the magnesium begins to burn, immediately place the cover on the crucible (using tongs) and remove the
burner.
5. After the reaction has subsided and "smoke" production has ceased, replace the burner and continue to heat
the crucible. Every 2 or 3 minutes, remove the burner and check the progress of the reaction by using tongs to
lift the lid of the crucible. CAUTION: Do not lean over the crucible. Then replace the lid and again apply heat.
After 10 minutes of heating, remove the burner and check the product. When the reaction is completed, the
magnesium should be completely converted to a light gray powder, magnesium oxide. If no ribbon-like
material remains in the crucible, place the crucible in a 250ml beaker to cool completely. If ribbon-like material
remains, heat the covered crucible an additional 10 minutes, then place the crucible in the beaker to cool.
DAY -2
6. Remove your crucible from the beker and heat for 5 minutes. Allow the crucible to cool then find
the combined mass of the crucible, crucible lid, and magnesium oxide. Record on the DATA TABLE.
DATA TABLE:
Mass of crucible and lid. = _______ g
Mass of the crucible, crucible lid, and the magnesium. = _______ g
Mass of the crucible, crucible lid, and magnesium oxide. = _______ g
3
CALCULATIONS:
7. Determine the mass of magnesium ribbon used in the experiment by subtracting the mass of the
crucible and lid from the mass of the crucible, lid, and magnesium.
Mass of magnesium. = _______ g
8. Determine the number of moles of magnesium used. Remember: mass / atomic weight = number of moles.
the atomic weight of magnesium is 24.3 g / mole .
Number of moles of magnesium. = _______ Mole
9. Determine the mass of magnesium oxide that was formed by subtracting the mass of the mass of the
crucible and lid from the mass of the crucible, lid, and magnesium oxide.
Mass of magnesium oxide formed. = _______ g
10. Determine the mass of oxygen that combined with the magnesium.
Mass of oxygen = mass of magnesium oxide - mass of magnesium
Mass of oxygen that combined with the magnesium. = _______ g
11. Determine the number of moles of oxygen atoms that were used. This is elemental oxygen so use
16.0 g / mole for the atomic weight.
Number of moles of oxygen atoms that were used. = _______ mole
12. Calculate the ratio between moles of magnesium atoms used and moles of oxygen atoms used.
Remember, this is a simple division. Divide the number of moles of Magnesium by the number of
moles of oxygen. Round your answer to the nearest whole number, as we do not use part of an atom.
This represents the moles (and also atoms) of magnesium. The moles (and also atoms) of oxygen, are
represented by 1, because it was on the bottom of the division.
Moles of Magnesium : Moles of Oxygen
:
_______
___1___
13. Give the empirical formula for magnesium oxide that is indicated by your experimental data.
Empirical formula of magnesium oxide. = __________
4
Periodic Table of elements
The periodic table of elements is a basic reference in chemistry. It is an orderly arrangement of the
112+ elements, which include the elements symbol, atomic number, atomic weight and electron
configuration.
Each element has its name represented by a symbol. The symbol is always represented by a capital
letter and in some cases followed by a lower case letter. Some elements are represented by the first
letter in their name and a later one while others are represented by letters from their Latin word.
List the symbol for the following elements:
Boron____
Flourine_____ Iodine_____ Silicon_____ Argon_____ Arsenic____ Rubidium____
Copper_____ tin_____
potassium_____
sodium_____ silver______
**Note that the elements are arranged in horizontal rows can vertical columns. The horizontal rows
represent periods. There are seven periods just as there are 7 energy levels.
The horizontal rows are called _____________.
What period is the element potassium in? _____________
What period is the element carbon in? ____________.
** The vertical columns divide the elements into groups/families. Group IA, IIA,IIIB, ect. All the
elements of the same group have similar chemical properties.
Vertical columns are called _______________.
What group is the element sulfur in? ___________
Chlorine and iodine are in what group? __________
Elements are in the same group because they have similar ______________________________.
The horizontal arrangement of the elements in by atomic number, beginning with one and proceed left
to right.
The atomic number of an element is the same as the number of protons in the nucleus of the atoms.
This number will never change because protons never leave the atom.
How many protons does carbon have?__________
What is the atomic number of carbon?__________
All atoms are neutrally charged. The negatively charged electrons cancel out the positively charged
protons. Since protons equal electrons the atomic number also tells the number of electrons.
How many electrons does oxygen have?_________
How many electrons does argon have?_________
Protons have a mass of 1AMU
Neutrons have a mass of 1 AMU
Electrons are so small that they are considered to have no mass
***So if the atomic mass is known the number of neutrons in an atom of an element can also be
determined.
Atomic mass = protons + neutrons
Neutrons = Atomic mass – protons
PROTONS = ATOMIC NUMBER= ELECTRONS
5
How many protons are in nitrogen?________
What is the atomic mass of nitrogen?_________
How many electrons are in nitrogen?_________
How many neutrons are in chlorine?_________
What is the atomic weight of boron?_________
Atoms of the same element having different mass numbers (protons + neutrons) are called isotopes.
The atomic number must be the same for the two atoms to be the same element but the number of
neutrons must differ.
What is the difference between these two elements of uranium?
Uranium –235
Uranium- 238
Complete the following chart
Element
Symbol
Atomic
Name
Number
Atomic
Mass
At. Mass Number of Number of Number of
rounded to electrons
protons
neutrons
whole #
Hydrogen
Helium
Boron
Carbon
Nitrogen
Copper
Calcium
Iron
Chlorine
Fluorine
Silver
Mercury
Barium
Radium
Gold
Argon
Xenon
The electrons located in the last energy level are called valence electrons. For example, oxygen has
an electron configuration of 1s22s22p4.
What is the last energy level of oxygen? _________
How many electrons are located in the outer energy level? _______
Sodium belongs to group ________. Its electron configuration is ______________________;
therefore it has _____ valence electrons. Because sodium has _______ valence electron, each
member of the IA family would have ______ valence electron.
6
Chlorine belongs to group _______ and its electron configuration is ________________; therefore Cl
has _____ valence electrons and each member of the VIIB family would also have ______ valence
electrons.
The most stable group of elements is group VIII called the Noble Gases. Neon belongs to group
_______ and has an electron configuration of _____________________. Therefore, neon has ______
valence electrons. Neon has _____ electrons in the 2s level and ______ in the 2p level. Meaning that
the sublevels of neon are completely _____________.
Atoms lose or gain electrons in chemical reactions to fill or empty completely their s and p sublevels;
therefore gaining a structure similar to the noble gases. Sodium has the electron configuration
1s22s22p63s1. To completely fill the s and p sublevel of the third energy level the sodium atom would
have to gain ______ electrons. To completely empty the 3rd energy level the sodium atom would have
to lose _____ electron(s). Do you think that it would be easier to lose 1 or gain 7 electrons?
_____________________
What could Chlorine do to attain a stable structure? _____________________________
When an atom gains or loses and electron it becomes an ion. Ions are atoms that have gained a stable
noble gas structure by gaining or losing electrons. An atom that has lost an electron is called a
___________ and has a ____________ charge. An atom that has gained an electron is called an
____________ and has a ______________ charge.
Sodium loses one electron when it enters into a chemical reaction. This would give sodium a +1
charge because it lose an electron. The cation now has one more proton than electron. An atom such
as chlorine, when it gains one electron has a ____ charge, because it has one more electron than
proton.
Looking at the Periodic Table do you notice any differences between the groups and columns?
Elements will gain or lose electrons to fill an energy level to become more stable and have the electron
configuration of the Noble Gases
Complete the chart below by writing the atom configuration, number of electrons lost or gained, ion
configuration and ion charge.
Element
Lithium
Beryllium
Chlorine
Sodium
Flourine
Oxygen
Neon
Aluminum
Nitrogen
Carbon
Electron
Configuration
# of valence
Electrons
# of Electrons
gained/ lost
7
Ion Charge
Nobel Gas it
will act like
Group
Ion Charge
# of Valence electrons
IA
II A
III A
IV B
VB
VI B
VII B
VIII
_____
_____
_____
_____
_____
_____
_____
_____
_____
_____
_____
_____
_____
_____
_____
_____
The valence electrons, of each element, determines its chemical and physical properties. We can
predict the reactivity of elements, if the ionization potential is known. Metals try to lose electrons,
nonmetals try to gains and noble gases remain unchanged. Since metals can easily lose electrons be
cause of low ionization potential they are very reactive. So when ionization potential decreases
reactivity increases.
As one proceeds down a column of the Periodic Table the ionization potential of metals ___________
(increases/decreased) therefore the reactivity ____________ (increases/decreases). The most reactive
metals would be those at the ________ (top/bottom) of the column.
As one proceeds across the rows of a Periodic Table the ionization ____________
(increases/decreases) therefore the reactivity ____________ (increases/decreased). The most reactive
metals would be those on the _________ (left/right) in the row.
What is the most reactive element on the chart? ___________
What is the least reactive element on the chart? ___________
By finding their position on the Periodic Table determine the element with the greatest reactivity and
circle it.
K or Rb or Cs
Al or Ga or In
Ra or Ba or Be
Cr or Mn or Fe
Pd or Cd or Sn
Os or Au or Cs
Fe or Mn or Ni
K or H or Fr
Au or Pt or W
The Periodic Table is divided into three sections –metals, nonmetals, and noble gases. The metals are
located on the left of side of the table. The nonmetals are located in the upper right hand corner.
Noble gases are the very last column to the right.
8
Label the following as metals, nonmetals, and noble gases.
Calcium____
Fe ____
Sb____
Iodine ____
Oxygen ____
Nb ____
Ar ____
Rubidium ____
Hydrogen ____
Au ____
S ____
Krypton ____
Nomenclature
There are over 12 million known chemical compounds in the world and each individual compound
requires a unique name - preferrably a descriptive name that tells us something about the compound. A
name that identifies the compound as belonging to a particular class of compounds (ionic vs. covalent,
inorganic vs. organic, etc.) and provides information about the chemical composition (and structure) of
the compound would be ideal. Such a system of naming chemical compounds requires a set of rules,
and this set of rules is known as nomenclature. Nomenclature is the systematic approach to naming
chemical compounds.
We are only concerned with naming very simple compounds. For this course, we will learn the
nomenclature rules for three very broad classes of compounds (ionic compounds, binary covalent
compounds, and acids). Each class of compounds has a different set of nomenclature rules, so you
need to know what type of compound you're dealing with before you even begin. Use the flowchart
below to help you determine the type of compound and the nomenclature rules.
Naming Compounds
Binary Compounds containing a metal and nonmetal
Rules for naming:
1) Place the name of the metal first in the name
2) Place the name of the nonmetal last in the name, using the stem of the word plus –ide
Example: BaCl2 – barium chloride
9
Formula Name
ZnS
CaCl2
CaO
MgS
Formula Name
BaO
SrI2
K2S
KF
Binary Compounds containing a transition metal and nonmetal
Rules for naming:
1. Place the name of the transition metal first in the name
2. Determine the charge the of the transition metal. Place the charge of the transition
metal after is name as a roman numberal
3. Place the name of the nonmetal last in the name, using the stem of the word plus –ide
Example: CuO – Cu+2 O-2 copper II oxide
Formula Name
FeO
CuO
ZnCl2
Ni2O3
Formula Name
Cr2O3
CdI2
NiS
MnF2
Binary Compounds containing a nonmetal and nonmetal
Rules for naming:
1) Give the Greek prefix to indicate the number of atoms of the first element in the
formula, except when there is only one.
2) Add the name of the first element in the formula.
3) Give the Greek prefix that indicates the number of atoms in the second element of the
formula.
4) Add the stem of the second element
5) Add the ending –ide
Greek prefixes
1-mono
2-di
3-tri
4-tetra 5-penta 6-hexa 7-hepta 8-octa
9-nona 10-deca
Example: SO2 -sulfur dioxide
Formula Name
CO2
SO3
As2O5
Cl2O
Formula Name
N2O
PCl5
F2O
CO
10
Ternary Compounds containing a metal and a polyatomic ion
Compounds that are formed by bonding more than two elements are call ternary compounds.
Rules for naming:
1) Name the metal
2) Name the polyatomic ion
Example: K2CrO4 - Potassium Chromate
Formula
Mg(OH)2
Name
_____________________________________________________
Na2SO4
_____________________________________________________
K3PO4
___________________________________________________________________
KNO3
___________________________________________________________________
Li2SO4
___________________________________________________________________
Al(NO3)3
_____________________________________________________
Na2 (HCO3) _____________________________________________________
Naming Ionic Compounds
Name the following ionic compounds:
1)
NH4Cl _____________________________________
2)
Fe(NO3)3 _____________________________________
3)
TiBr3 _____________________________________
4)
Cu3P _____________________________________
5)
SnSe2 _____________________________________
6)
GaAs _____________________________________
7)
Pb(SO4)2 _____________________________________
8)
Be(HCO3)2 _____________________________________
11
Common Polyatomic Ions
+1 CHARGE
ion
-1 CHARGE
name
ion
-2 CHARGE
name
ion
name
-3 CHARGE
ion
name
NH4+ ammonium H2PO3-
dihydrogen
phosphite
HPO32-
hydrogen
phosphite
H3O+ hydronium H2PO4-
dihydrogen
phosphate
HPO42-
hydrogen
PO43- phosphate
phosphate
Hg22+ mercury(I) HCO3-
hydrogen
carbonate
CO32-
carbonate
PO23- hypophosphite
HSO3-
hydrogen
sulfite
SO32-
sulfite
AsO33- arsenite
HSO4-
hydrogen
sulfate
SO42-
sulfate
AsO43- arsenate
NO2-
nitrite
S2O32-
thiosulfate
nitrate
2-
-
NO3
-
OH
hydroxide
-
CH3COO acetate
CrO2
-
CN-
C2
carbide
2-
oxalate
2-
chromate
C2O4
chromite
CrO4
cyanide
Cr2O72-
dichromate
cyanate
C4H4O6 tartrate
-
thiocyanate
MoO42-
superoxide
2-
peroxide
2-
disulfide
CNS
-
O2
-
MnO4
-
ClO
ClO3-
chlorate
ClO4
O2
molybdate
hypochlorite
chlorite
ClO2
2-
permanganate S2
-
-
-
BrO
perchlorate
hypobromite
BrO2
-
bromite
BrO3
-
bromate
BrO4
-
perbromate
-
IO
hypoiodite
IO2-
iodite
-
iodate
IO3
-
IO4
AlO2
N3
silicate
2-
-
CNO
-
SiO3
periodate
-
aluminate
azide
12
PO33- phosphite
-4 CHARGE
ion
name
P2O74- pyrophosphate
Rules for Writing Metal-Nonmetal Formulas
1. Write the symbol of the metal first. The charge is above the symbol in the Periodic Table.
2. Write the symbol of the nonmetal next. The charge is above the symbol in the Periodic Table.
3. Add subscripts to balance the positive and negative charge.
Example: Sodium oxide Na +1 O -2
1(2) + -2 = 0
Na2O
Name
Formula
Aluminum oxide Al +3 O -2
3 (2) + -2(3) = 0
Al2O3
Name
Formula
Lithium sulfide
Strontium oxide
Rubidium oxide
Calcium chloride
Potassium oxide
Barium bromide
Sodium nitride
Lithium fluoride
Rules for Writing Transition Metal-Nonmetal Formulas
1. Place the symbol of the metal first- the Roman number indicates the charge.
2. Place the symbol of the nonmetal next. The charge is above the symbol in the Periodic Table.
3. Add subscripts to balance the charges.
Example: Copper I oxide Cu +1 O -2
1(2) + -2 = 0
Cu2O
Name
Formula
Iron III oxide
Name
Lead II oxide
Iron III sulfide
Copper I sulfide
Manganese III
chloride
Nickel II fluoride
Iron III bromide
Nickel II Oxide
Manganese II
bromide
13
Fe +3 O -2
3 (2) + -2(3) = 0
Fe2O3
Formula
Rules for Writing Nonmetal-Nonmetal Formulas
1. Write the symbol for the first nonmetal, followed by the subscript indicated by the prefix.
2. Write the symbol for the second nonmetal, followed by the subscript indicated by the prefix.
Prefixes:
1-mono
6-hexa
Example: Sulfur trioxide
Name
2- di
7-hepta
3- tri
8-octa
SO3
Sulfur hexafluoride SF6
Formula
4- tetra
9- nona
5- pent
Chlorine trifluoride
Name
Monohydrogen
dioxide
Dinitrogen
Pentachloride
Tetraphosphorous
Dioxide
Nitrogen Dioxide
Dihydrogen dioxide
Chlorine monoxide
Sulfur hexafluoride
10-deca
Formula
Write the formulas for the following compounds:
10)
chromium (VI) phosphate _____________________________________
11)
vanadium (IV) carbonate _____________________________________
12)
tin (II) nitrite _____________________________________
13)
cobalt (III) oxide _____________________________________
14)
titanium (II) acetate _____________________________________
15)
vanadium (V) sulfide _____________________________________
16)
chromium (III) hydroxide _____________________________________
17)
lithium iodide_____________________________________
18)
lead (II) nitride ____________________________________
14
Identify the first element of each compound as a Metal, Trans Metal or Non Metal then name each
compound
1. ZnS M zinc sulfide
26. CuCl2 _____________________________
2. MgCl2 _____________________________
27. PCl5 _____________________________
3. Ca(HPO4)__________________________
28. LiNO2 _____________________________
4. CaSO4 _____________________________
29. K3PO4 _____________________________
5. AgNO3 ____________________________
30. CuCN _____________________________
6. Li2S _______________________________
31. KHCO3 _____________________________
7. CaO _______________________________
32. NaHSO3 _____________________________
8. H2CO3 _____________________________
33. Li2HPO4 _____________________________
9. Mg3(PO4)2 __________________________
34. Li3PO3 _____________________________
10. KCl _______________________________
35. MgSO4 _____________________________
11. K2O _______________________________
36. Ca(OH)2 _____________________________
12. Al(NO2)3 ____________________________
37. SiO2 _____________________________
13. MgO _______________________________
38. CuCl _____________________________
14. SnI2 _______________________________
39. KCl _____________________________
15. AsCl5 ______________________________
40. CaSO3 _____________________________
16. CuSO3 _____________________________
41. NaBr _____________________________
17. LiF ________________________________
42. P2O3 _____________________________
18. FeSO4 ______________________________
43. ClO _____________________________
19. SnCl4 _______________________________
44. NO2 _____________________________
20. AsCl3 _____________________________
45. NaF _____________________________
21. KCN ______________________________
46. ZnS _____________________________
22. NaOH ____________________________
47. Pb(NO3)2 _____________________________
23. Fe(OH)3 ___________________________
48. CaSe _____________________________
15
ASSIGNMENT -- Write the formulas for the following compounds:
51. lithium chloride ________________
76. strontium carbonate ________________
52. phosphoric acid ________________
77. calcium nitrate ________________
53. boron trichloride ________________
78. disulfur dichloride ________________
54. ferric chloride ________________
79. tin (IV) oxide ________________
55. carbon tetrachloride _______________ 80. sodium bicarbonate ________________
56. silver sulfide ________________
81. strontium chlorate ________________
57. antimony trichloride _______________ 82. aluminum hydroxide ________________
58. barium carbonate ________________ 83. cadium nitrate ________________
59. iodine monochloride ______________ 84. diphosphorus trioxide ________________
60. aluminum nitride ________________ 85. sodium hydride ________________
61. lead sulfate ____________________ 86. calcium nitride ________________
62. ammonium chloride _______________ 87. sulfur trioxide ________________
63. hydrogen fluoride ________________ 88. aluminum nitrate ________________
64. hydrobromic acid ________________ 89. silver oxide ________________
65. tin (II) bromide _________________ 90. ammonium phosphate ________________
66. cuprous oxide __________________ 91. cupric sulfate ________________
67. calcium bicarbonate ______________ 92. lithium fluoride ________________
68. copper (II) cyanide _______________ 93. sodium sulfate ________________
69. cesium fluoride __________________ 94. radium carbonate ________________
70. zinc phosphate __________________ 95. copper (II) oxide ________________
71. dinitrogen pentoxide ______________ 96. iron (III) sulfate ________________
72. iron (II) sulfate ___________________ 97. magnesium perchlorate _______________
73. bromous acid ____________________ 98. potassium hypochlorite ________________
16
Percentage Composition Calculations
M&M Lab:
Red
Green
Brown
Orange
Yellow
Color/Whole #
Percent of
To calculate the correct percentage composition of each element in some compound you must correctly
follow several steps. It is not very difficult, once you get the hang of it. Please take notes on the steps
to follow.
Lets look at a sample problem: magnesium chloride --> Mg Cl2
step 1: calculate formula mass
24.3 + 2(35.4) =
24.5 + 70.8
= 95.1
step 2: divide each component mass by the formula mass and multiply by 100
Mg: 24.3/95.1 x 100 = 25.6%
Cl: 70.8/95.1 x 100 = 74.4%
step 3: make certain the percentages add up to 100 (+/- 0.1)
25.6 + 74.4 = 100
Determine percent composition for each element in the compound
Na2CO3
P2O5
NH3
FeSO4
phosphorus trifluoride
vanadium (V) oxide
aluminum hydroxide
zinc sulfide
17
Percent Composition of Gum
General Goal(s): Students will understand the concept of percent composition of compounds and be
able to perform the associated calculations. A lab will be used to reinforce the concept.
Specific Objectives: Students will be able to define percent composition. Students will be able to
calculate the percent composition of a compound.
Anticipatory Set :
How do you calculate percent?
How do you calculate the grade on your test?
Do examples:
NaCl
% Na =
CaF2
% Ca =
%Cl =
KNO3
%K =
%N =
%O =
%F=
Na2SO3
%Na =
%S =
%O =
Lab Activity: Calculate Percent Composition of Chewing Gum
We're assuming chewing gum has 2 components - gum and sugar. The sugar will dissolve when you
chew it, leaving behind only the gum. Thus we can calculate the percent of sugar in the gum.
This works best with 4-5 students in a group. Each student gets a piece of gum.
Get the mass of a paper cup. Unwrap the gum and put all sticks in the cup. Get the mass of the gum +
cup. Calculate the mass of the gum. (This is "total" gum - includes gum and sugar).
Each person chews their piece of gum for 5 minutes.
Mass of gum and sugar. __________
Mass of gum chewing. ________
Calculate the mass of sugar in the gum. (Total gum - chewed gum)
Calculate the moles of sugar in the gum.
Calculate the percent sugar in the gum.
Conclusion Questions:
1) Would a dentist recommend chewing this gum? Why or why not?
2) Why is it good to chew gum if you cannot brush your teeth right away?
18
EMPIRICAL & MOLECULAR FORMULA
An empirical formula gives the ratio of atoms in a compound. Molecular formula tells how many
atoms are in a compound. If a compound's empirical formula is C6H12O6, it will have a molecular
formula of C6H12O6, C12H24O12, and so on.
The term "empirical" refers to the relative percent composition of a pure chemical substance by
element.
Let's find this compound's empirical formula:
First we will assume that we have 100 grams of this compound. So, in 100 grams, there will be 40.00
grams of C (carbon), there will be 6.72 grams of H (hydrogen), there will be 53.29 grams of O
(oxygen). Next, we will compare each element. Before we can compare them, we need to convert them
to moles:
Now that we know the moles of each element, we can compare the different elements and determine
the empirical formula. We do this by dividing all of the mole quantities by the smallest one. In the
example above, the smallest mole quantity would be either carbon or oxygen (3.331 mol):
We now know that the ratio of C:H:O is 1:2:1, which makes the empirical formula CH2O. Let's
suppose we use a molecular weight of 180 g/mol for this compound. Knowing this, we can now
determine the molecular formula. The formula weight of our empirical formula is 30 g/mol. To find the
multiple, divide the molecular weight by the empirical formula weight:
The molecular formula has a multiple of 6:
C(1 x 6) H(2 x 6) O(1 x 6) which results in C6H12O6
19
Percent Composition & Empirical Formulas
A. Calculate the percent composition for the following compounds.
1. Cr2O3
2. iron (III) oxide
B. Determine the empirical formula for each compound.
3. A compound contains 0.0130 mol carbon, 0.0390 mol hydrogen, and 0.0065 mol oxygen.
4. A compound consists of 70.0% oxygen and 30.0% nitrogen by mass.
5. Glucose contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass.
6. Phosphoric acid is found in some soft drinks. A sample of phosphoric acid contains 0.3086 g of
hydrogen, 3.161 g of phosphorus, and 6.531 g of oxygen.
C. Determine the molecular formula for each compound described.
7. A compound has an empirical formula of NO2 and a molar mass of 92.02 g/mol.
8. A compound has an empirical formula of C2H3O and a molar mass of 172 g/mol.
9. Ibuprofen, a common headache remedy, has an empirical formula of C7H9O and a molar mass of
approximately 215 g/mol.
10. Nicotine is 74.1% carbon, 8.6% hydrogen, and 17.3% nitrogen by mass. Its molar mass is about
160 g/mol.
11. 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
180g/mol.
20
1. Determine the empirical formula of each of the following compounds if a sample contains
a. 0.104 mol K, 0.052 mol C, and 0.156 mol O
b. 5.28 g Sn and 3.37 g F
c. 87.5 percent N and 12.5 percent H by mass
2. Determine the empirical formulas of the compounds with the following compositions by mass
a. 10.4 percent C, 27.8 percent S, and 61.7 percent Cl
b. 21.7 percent C, 9.6 percent O, and 68.7 percent F
3. Determine the empirical and molecular formulas of each of the following substances:
a. ibuprofen, a headache remedy contains 75.69 percent C, 8.80 percent H, and 15.51
percent O by mass; molar mass about 206 g
b. epinephrine (adrenaline), a hormone secreted into the bloodstream in times of danger or
stress: 59.0 percent C, 7.1 percent H, 26.2 percent O, and 7.7 percent N by mass; MW
about 180 amu.
21
Analyzing the “Pop” in Popcorn
Introduction:
Corn is a common foodstuff, native to the Americas, which appears in many forms: corn on the cob,
corn off the cob, creamed corn, and popcorn. There is also field corn that is fed to livestock and
colored corn that is hung on our doors in autumn. Each variety of corn contains a different amount of
water, sugars and starches. Popcorn is a favorite evening snack. Popping popcorn involves heating the
corn until the vapor pressure of water inside the kernel is great enough to cause it to burst, turning the
kernel inside out and releasing the trapped water vapor.
Purpose:



Determine the percent of water in popcorn.
Determine the moles of water in popcorn.
Use the ideal gas law to determine the pressure inside the kernel when it pops
Safety:
1. Wear protective goggles throughout the laboratory.
2. Heat the flask evenly to prevent the oil from spattering, boiling oil is hotter than boiling water.
3. Do not eat the popcorn popped in lab. It may be contaminated with chemicals from other
laboratory investigations.
4. Thoroughly wash your hands before leaving the laboratory.
Procedure:
I. Finding the mass of 16 kernels of popcorn
II. Finding the volume of popcorn
1. Using the water displacement method, find the volume of the 16 kernels using the 25-mL
graduated cylinder.
2. Use paper towels to dry the kernels before proceeding.
III. Finding the mass of water in popcorn
1. Add one pipette of cooking oil and the 16 kernels of popcorn to a clean, dry 125-mL Erlenmeyer
flask.
2. Determine the mass of the flask, oil and unpopped popcorn.
3. Cover the flask with aluminum foil. Cut slits in it to allow water vapor to escape.
4. Pop the popcorn with a Bunsen burner. Slowly move the burner back and forth to avoid burning
the popcorn. If the popcorn burns, you will need to start over.
5. Remove from heat when most of the kernels have popped.
6. Remove the aluminum foil. If there is water vapor on the inside of the flask, use a paper towel to
wipe away. Set on the lab table to cool.
7. Determine the mass of the flask, oil and popped popcorn.
8. Throw popped popcorn in a trashcan. Wash Erlenmeyer flask in soapy water, rinse, and dry.
9. Wash your hands thoroughly.
22
Data:(Include appropriate labels)
Mass of popcorn - ____________
Volume of popcorn ____________
Volume of popcorn in L (dm3) - ____________
Mass of flask, oil, and unpopped popcorn - ____________
Mass of flask, oil and popped popcorn ____________
Mass of water in the popcorn ____________
Molecular mass of water
____________
Calculations:
1. What is the percent of water in the popcorn?
2. How many moles of water were in the popcorn?
3. What was the water pressure at the time of the “pop”? PV = nRT.
Assume that the popcorn pops at the boiling point of the cooking oil (225oC).
Questions:
1. What is standard atmospheric pressure? ___________________
2. Assuming the atmospheric pressure is standard, how does the pressure need to pop corn compare
with atmospheric pressure?
3. Name two sources of error (NOT INCLUDING MEASURMENTS OR CALCULATIONS OR
MEASURING DEVICES!
23
Mixed Practice: Names and Formulas
First determine whether each of the following compounds is ionic (M + NM), polyatomic (3 or
more atoms), or covalent (2 NM’s). Then write the name for each compound.
1) NO2 __________________________________________
2) NaBr __________________________________________
3) SiO2 __________________________________________
4) P2Br4 __________________________________________
5) FeSO4 __________________________________________
6) SF6 __________________________________________
7) Li2S __________________________________________
8) MgBr2 __________________________________________
9) carbon monosulfide __________________________________________
10) vanadium(II) phosphide __________________________________________
11) oxygen difluoride __________________________________________
12) gold(I) phosphate __________________________________________
13) triboron tetrahydride __________________________________________
14) aluminum carbonate __________________________________________
15) dinitrogen heptoxide __________________________________________
16) dinitrogen trioxide __________________________________________
17) cadmium chloride __________________________________________
18) aluminum oxide __________________________________________
19) disulfur trichloride __________________________________________
20) cobalt(II) acetate __________________________________________
24
Self Test
Complete the following chart
Element
Symbol
Atomic
Name
Number
Atomic
Mass
At. Mass Number of Number of Number of
rounded to electrons
protons
neutrons
whole #
Krypton
Radon
Lead
Uranium
Write the chemical formulas:
SnSe2 _____________________________________
GaAs ____________________________
Pb(SO4)2 _____________________________________
Be(HCO3)__________________________
Mn2(SO3)3 ___________________________________
Al(CN)3 ___________________________
Write the formulas for the following compounds:
(a) chromium (VI) phosphate ______________
(b) vanadium (IV) carbonate _______________
(c) tin (II) nitrite _______________
(d) cobalt (III) oxide ____________
Give the percent composition for the formulas (a-d) above:
(a)
(b)
(c)
(d)
Element
Atom
Configuration
# of
electrons
gained or
lost
Ion
Configuration
Rubidium
Bromide
Potassium
Silicon
25
Ion Charge
Number of
Valence
Electrons
26