Reactions between simple models of biomolecular compounds ...
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Objective 4 1
Objective 4: use models for describing compounds and chemical reactions
This objective is further broken down into 3 outcomes
Outcome 4A: Demonstrate models of ionic and molecular compounds
Outcome 4B: Describe reactions by using word equations, chemical formulas, and molecular models and identify types of reactions
Outcome 4C: Balancing simple chemical reactions
Outcome 4A: Demonstrate models of ionic and molecular compounds
Models Models are often used
to show which elements are
making up either ionic or
molecular compounds and can
be either drawn with the atoms
directly touching, or with a
line attaching the atoms which
represent the bond between
them. They also show the
numbers of atoms that are making up the compound. When drawing models (either ionic or molecular)
the size of the atoms will represent which has a larger
atomic mass (look to the periodic table to find out as it is
arranged in order of increasing atomic mass). In the H2O
example, oxygen has a higher atomic mass than hydrogen
and will therefore be drawn larger. If there is more than
one atom of an element, this is shown in the subscript of
the chemical formula. For example, H2O is the chemical
formula for water and since there are two Hydrogen atoms,
the number 2 is written as a subscript. Once you know the
elements and the number of atoms, you can draw the
model.
The number of atoms can be counted by looking at a model or by looking at the chemical
formula. For example, it you look at the model of NaCl above, you can count 2 atoms. This can also be
determined by simply looking at the chemical formula NaCl. If a compound has many more atoms, you
just simply count them up. For example, the chemical formula for sodium acetate is NaC2H3O2. You can
see there are 4 elements that make up sodium
acetate but if you count the total number of
atoms you get 8. Another example: A certain
compound’s formula is NaHCO3C. There are 4
elements and 6 atoms that make up this formula
(carbon is found in 2 different places in the
compound but you can’t count it twice because it’s still carbon).
Objective 4 2
A subscript can also be used to indicate whether an element or compound is currently in a solid,
liquid, or gas state. For example, H2O(s) indicates that you are looking at water’s solid form (ice). H20(l)
would indicate the compound is currently in its liquid state, and H20(g) would indicate that water has
been boiled and is in its gaseous form. There is one more subscript you need to know. The subscript (aq)
stands for “aqueous” and means the compound is dissolved in water. For example, if salt (NaCl) was
dissolved in water, its chemical formula would be written as NaCl(aq)
In the examples above, different elements are indicated by different sizes. But there are many
different ways that models can represent different elements. Another common way is simply to use
different colors. For example, in the diagram below, hydrogen is represented as a different color than
oxygen, even though in
reality hydrogen atoms
are much smaller.
In the two
examples on the
previous page, different sizes and colors were used to identify which element was which. Sometimes,
however, there is no way to tell. For example, sometimes models only
represent the number of total atoms present as shown in the diagram to the
right. There is no way to tell which atom to the right is the sulfur atom and
which 3 are the hydrogen atoms. These models still may give you some
information however. For example, if you asked if the model to the right were
SeO3 or C4H, you would pick SeO3 based on the fact that SeO3 has 4 total
atoms and C4H has 5 total atoms.
Objective 4 3
1. Complete the table below. Remember to draw the proper size of the elements in relation to each other. Also,
when writing in the chemical formula, make sure you put in the subscript to indicate its state of matter. Boxes
with an in them don’t have to be done Chemical
formula
Model model (use different sizes for
different atoms)
# of elements # of atoms State of matter chemical found in
BeO(l)
….
2 2 Liquid………….
PO2(g)……….
.
2 3 Gas
Mg3P2(s) …….……
2 5 Solid…………
C12H22O11(aq)
(common name
is sugar)………
3 45 Dissolved in water
Use the following information to answer the next question
CrC2H3O2H
2. How many elements are found in the above compound? How many atoms are there?
4 elements. 9 atoms.
3. Match each compound with its model by placing the number next to the chemical formula underneath the
appropriate model.
1. N2 2. CO 3. nitrogen dioxide 4. Beryllium phosphoride 5. MgF2
2 5 3 1 4
---
---
Objective 4 4
Use the following information to answer the next question
4. What is the chemical formula for the compound on the right above?
A. S2Cl5P3 B. S2Cl4P4 C. S3Cl4P3 D.S3Cl3P4 E.S4Cl3P3 F.S4Cl4P2
D
Use the following information to answer the next question
I.
II
III
IV
5. Which of the above models is modeling C3H?
III Use the following information to answer the next question
6. Which of the following formulas could the model above represent?
A. S2 B. F2Br C. MgC3 D. CFCO
B
Use the following information to answer the next question
7. Which of the following formulas could the marshmallow model above represent?
A. He3 B. B2P C. NC3 D. BrCl
C ……………..
Objective 4 5
Use the following information to answer the next question
8. Write the chemical formula for the compound on the above right (it doesn’t matter what order you put the elements in)
H5S2N4
9. Fill in the chart. Show your work for balancing ionic compounds
Elements to
combine chemically
into compounds:
Ionic or
Molecular
Chemical formula (you
may need to look at
outcome 3D again if you
forget how to do this)
Chemical name (you may
need to look at outcome 3B
again if you forget how to do
this)
Model (use different
sizes for atoms)
# of
atoms
Lithium and fluorine
I
LiF
lithium fluoride
2
Two sulfur and one
chlorine atom
M
S2Cl
disulfur monochloride
3
Beryllium and
fluorine
I
BeF2
beryllium fluoride
3
Iron (2+) and
phosphorus
I
Fe3P2
Iron (II) phosphoride
5
Two nitrogen atoms
M
N2
nitrogen gas
2
----
Objective 4 6
Outcome 4B: Describe reactions by using word equations, chemical formulas, and molecular models and identify types of reactions
Word equations In previous outcomes you have looked at how elements combine to form compounds. You have looked
at the difference between ionic and molecular compounds and how to name each of them. You have also
learned how to model these compounds with molecular models. But what happens when these ionic and
molecular compounds react with elements or other compounds? In this outcome you will learn about some
common chemical reactions and how to represent them with word equations, chemical formulas, and molecular
models
All chemical reactions, whether simple or complex, involve changes in substances. One or more starting
substances (the reactants) are changed into one or more new substances (the products). In a word equation, the
reactants are written on the left, and the products are written on the right. They are connected by an arrow ( )
that is read as "yields" or "reacts” to produce."
Reactants Products Word equations are simply a different way of writing the chemical formula for a chemical reaction. The
models simply represent the chemical formulas and word equations in a visual way. Below is an example of a
chemical word equation which represents a chemical reaction. When writing the word equations, common
names are used if a compound has a common name (like methane or water). If a compound doesn’t have a common name, it is simply named using the naming systems learned in previous outcomes (like tricarbon
dioxide or sodium sulfide).
Chemical Formula H2O + H H4O
Word Equation water + hydrogen tetrahydrogen monoxide
Model
(Do not worry if the atoms do not
balance. There are only 3 hydrogen
on the reactant side but 4 on the
product side. You will learn how to
balance these in the next outcome)
+
NOTE: In the reaction above, you may have noticed that an “extra” hydrogen seemed to appear in the
product that wasn’t there in either of the reactants (the reactants only had three hydrogen, but the product has four.) This is because in this topic you are not required to balance chemical reactions. For now, just be able
to name each individual element or compound and be able to recognize the 3 types of reactions found below
(combustion, corrosion, replacement reactions).
Chemical Reactions The word equation, chemical formula, and model above represent a chemical reaction. While there are
many types of chemical reactions, you are going to learn how to identify just three: corrosion reactions,
combustion reactions, and replacement reactions
Combustion Reaction A combustion reaction is a reaction involving a fuel (which almost always has the element carbon in it)
and oxygen. In a combustion reaction heat is produced. When combined, the fuel is used up and heat is
released. The burning of paper, wood, or gasoline are examples of combustion reactions. Most combustion
reactions involve the burning of carbon in a substance. The
combination of the carbon and oxygen is what produces the
heat and light energy. All fossil fuels (gasoline, oil, propane,
coal, natural gas, methane) contain the element carbon
somewhere in their chemical formula. So do paper and wood.
Burning carbon will produce carbon dioxide gas (CO2(g)), which
is the main cause of global warming. The most basic
combustion reaction, involving pure carbon, is shown below.
Objective 4 7
Notice that although heat had to be produced, it isn’t included in the model. This is because heat isn’t made up of atoms.
Chemical Formula C(s) + O2(g) CO2(g)
Word Equation carbon + oxygen gas carbon dioxide
Model
+
While fossil fuels have carbon in them, they are not made of pure carbon. Therefore, most combustion
reactions will have a reactant that is made of carbon as well as other elements. Below shows the burning
(combusting) of methane, which is the main component of natural gas.
Chemical Formula CH4(g) + O2(g) CO2(g) + H2O(l)
Word Equation methane + oxygen gas carbon dioxide + water
Model
+ +
Corrosion reaction When some metals are exposed to oxygen they undergo
corrosion. You learned in previous outcomes that corrosion
is the decomposition of a metal. All corrosion reactions
involve a metal, oxygen and water. In fact, corrosion will not
occur if there is no moisture present. When iron corrodes, it
is called rusting and is shown in the diagram to the right and
in the example below. Corrosion occurs quicker if there is more moisture and if it is more heat. It is also
sped up if there is salt in the water. Note that water is not usually included as a reactant, but its presence is
needed to transfer the electrons needed for corrosion to occur. The reason it is usually not listed as a
reactant is because the water’s chemical makeup is not usually rearranged into a new chemical but is simply present as a way to move electrons around in order for the corrosion to occur. It’s the same reason that “heat” is not usually included as a reactant in combustion although a little bit of heat is needed in order for combustion to occur (also, heat is not made of atoms but is a type of energy).
Chemical Formula Fe(g) + O2(g) Fe2O3
Word Equation iron + oxygen gas iron (III) oxide
Model
+
Replacement reaction When a compound reacts with an element or another compound, one element may replace another. For
example, when pure zinc reacts with the compound copper (II) sulfide, zinc replaces the copper leaving
pure copper and zinc sulfide
(Zn + CuS Cu + ZnS). This
is called a replacement
reaction and is shown below.
Chemical Formula Zn + CuS Cu + ZnS
Word Equation zinc + copper (II) sulfide copper + zinc sulfide
Model
+
+
Objective 4 8
10. Write the word equation for this chemical reaction: Be + O BeO
beryllium + oxygen beryllium oxide
11. Write the word equation for this chemical reaction: O2 + S2O2 S2O4
oxygen gas + disulfur dioxide disulfur tetraoxide
12. Write the word equation for this chemical reaction: Na + Al2O3 Na2O + Al
sodium + aluminum oxide sodium oxide + aluminum
13. Write the word equation for this chemical reaction: H + P3H4 P3 H5
hydrogen + triphosphorus tetrahydride triphosphorus pentahydride 14. What two things are necessary for a combustion reaction to occur? What is ALWAYS produced in a
combustion reaction?
Necessary: Fuel, oxygen Always produced: Heat 15. What are 8 substances mentioned in the reading that contain the carbon needed for combustion to occur?
paper wood gasoline oil
natural gas coal methane propane 16. What three things are necessary for a corrosion reaction to occur?
A metal, oxygen and water (heat would speed up the reaction)
17. Identify the below reactions as a combustion, corrosion, or replacement reaction (water is not represented in
the corrosion reactions below, even though in reality it would need to be present).
I Cr + FeCl2 CrCl2 + Fe Replacement II Ti + O2 Ti2O3 Corrosion III Al + HCl AlCl + H Replacement IV C + O2 CO2 Combustion V CH3OH + O2 CO2 + H2O Combustion VI Mg + O MgO Corrosion
18. How many products are seen in IV above?
1
Objective 4 9
19. What 3 conditions will speed up a corrosion reaction?
More moisture, warmer, salt
20. In which example will corrosion currently be working on the metal the slowest?
A. A coin in the sand of the Sahara Desert on an extremely hot day
B. The metal bottom of a boat sailing near Hawaii in December
C. A nail in the roof of a house in Los Angeles on a rainy day in summer
A (corrosion needs moisture to occur)
21. Fill in the information for the following combustion reaction (don’t worry about balancing out number of atoms in the reactants and products)
Chemical Formula C2H6(g) ……. + O2(g) CO2(g)……... + H2O(l)……..
Word Equation ethanol (common name)
+ oxygen gas carbon dioxide + water
Model
+
+
………………
22. Fill in the information for the following corrosion reaction (don’t worry about balancing out number of atoms in the reactants and products)
Chemical Formula Mg +.. O2(g) . MgO…..………
Word Equation magnesium +.. oxygen gas.. . magnesium oxide
Model ...
+..
.
23. Fill in the information for the following replacement reaction (don’t worry about balancing out number of atoms in the reactants and products)
Chemical Formula Be….. + AlO……….. Al…… + BeO Word Equation beryllium + aluminum oxide aluminum + beryllium oxide..
Model
+
..
+
……
-------
Objective 4 10
Outcome 4C: Balancing simple chemical equations
Water (H2O) is a common name for one type of
compound that is very important to us (the chemical name
for water is dihydrogen monoxide). Water is necessary
for life as we know it on Earth and makes up 70% of a
humans body weight. There are a few more common
names that you must know. Hydrochloric acid is the
common name for HCl which is the acid found in our
stomachs but is also used in the production of many
foods, medicines and countless other products. Sodium
hydroxide has the chemical formula of NaOH and is
used in many strong household cleaners such as drain
cleaner and oven cleaner. You know that the symbol for
sodium is “Na” but you have not learned that when
oxygen and hydrogen combine they can form an ion
called a “hydroxide” ion (represented as: OH
- ). The Na
+
ion and the OH
- ion combine to form sodium hydroxide
(NaOH), which is a very powerful cleaning agent.
Ammonia is another chemical found in some cleaners
and has the chemical formula of NH3. The most common
cleaner it is found in is Windex. It is also used in many
areas of product production from fertilizers and food to
the production of rubber and metals. In fact, 80% of
ammonia is used in the production of fertilizers (nitrogen
is one of the main atoms needed for plants to grow).
Ammonia is also the chemical that gives cat urine that
strong potent smell. Another important chemical that is
given a common name is methane and has the chemical
formula of CH4. It is a fossil fuel similar to gasoline oil or
coal. All of these fossil fuels, including methane, have
carbon and you learned earlier in this unit that carbon is
almost always the fuel for combustion. Methane is also
the gas that cows burp out. Cows burping methane
doesn’t seem like a big deal, but this activity contributes largely to global warming. A cow will burp out 200
pounds of methane gas a year and there are 1.5 billion
cows on the planet raised for milk and meat. And
methane is a much more powerful greenhouse gas than
carbon dioxide. In fact, it traps heat 23 times more than
carbon dioxide.
Objective 4 11
You learned previously about modeling elements and compounds. In those models, each element was
represented as a circle (as seen in the diagram below on the left. However, it is also common for
compounds (along with their chemical structure) to be represented in just one large circle. For example,
water (H2O) can be modelled as seen below on the right:
The reason that molecules are commonly many of these water molecules joined together can get confusing
using the above method so it is simpler to draw them as seen below:
You see above that the number “4” is put in front of the H2O to indicate that 4 water molecules joined
together. It also indicates the number of total atoms. The 4 is multiplied by the subscript to give the total
number of atoms of each element in the larger molecule. Since 4 multiplied by 2 is equal to 8 we know
there are a total of 8 hydrogen atoms. And since 4 multiplied by 1 is 4, we know that there are 4 oxygen
atoms (remember that when there is no subscript written we know that is actually a 1). The number in front
is not only needed to represent the number of water molecules joined together to form the larger molecule
but is needed to balance chemical equations. For example, when oxygen gas (O2) and hydrogen gas (H2)
join they form water. But since oxygen and hydrogen are only found as diatomic molecules (O2 and H2
instead of just O or H as single atoms) it would seem that you can’t make H2O because two hydrogen and
two oxygen would make H2O2 (which is called hydrogen peroxide and is extremely poisonous). What it
means is that two hydrogen gas (H2) molecules will always combine with one oxygen gas (O2) molecule to
form two (H2O) molecules. This is seen in the reaction below:
Chemical
equation: 2H2 + O2 2H2O
Models:
+
2 hydrogen
gas
+ oxygen
gas
2 water
You can see that the number of hydrogen atoms in the reactants and the product is now equal. This is also
true of the oxygen atoms. The above chemical equation represents a reaction where compounds are joining
into larger compounds. Sometimes however, compounds are broken down. An example of this is seen
below as ammonia breaks down into nitrogen gas and hydrogen gas.
Chemical equation: 2NH3 N2 + 3H2
Models:
+
2 ammonia nitrogen gas + 3 hydrogen gas
You can see that throughout the breakdown of ammonia, the number of nitrogen and hydrogen atoms is equal
on each side of the chemical equation but that two ammonia molecules were originally needed for this reaction
to occur.
Objective 4 12
1. Give the common name for the following chemicals and give 1 fact about water and sodium
hydroxide and 2 facts about hydrochloric acid, ammonia and methane.
HCl NH3 H2O NaOH CH4
Common
name Hydrochloric
acid
Ammonia Water Sodium
hydroxide
methane
Fact Found in
our stomach.
Used in
making
many
products.
Used in
certain
cleaners such
as Windex.
Used in
production of
fertilizers and
other products
Makes
up 70%
of human
body
weight
Used in
strong
cleaning
agents
Is a fossil
fuel. Also
found in
cow burps;
leads to
global
warming
Use the following information to answer the next question
2. Answer the following questions based on the diagram of the structure above
How many types
of compounds
are seen above?
How many
elements are
found above?
How many
atoms of carbon
and hydrogen are
found above?
How many total
molecules are
found above?
How would you write the
chemical formula for the
molecules that are joined
above?
1 (methane) 2 3 carbon
12 hydrogen
3 3CH4
3. Fill in the chart below based on the title below in bold (it may be easier to start with writing the
chemical formula)
Four hydrochloric acid molecules are joined together
Write the chemical
formula
Draw a model How many atoms
are there?
How many
elements are there?
4HCl
8
2
Objective 4 13
Use the following information to answer the next question
4. How many types of compounds are seen to the right?
3 5. How many elements are seen to the right?
2 6. How many total molecules are seen to the right?
11 7. How many atoms are seen to the right?
29
8. Draw a model representing the breakdown of two water molecules into hydrogen gas and oxygen gas
Chemical equation: 2H2O. 2H2 +. O2
Models:
+.
9. Draw a model representing chlorine gas and hydrogen gas combining into joined hydrochloric acid
molecules
Chemical equation: Cl2 +.. H2 ...... 2HCl
Models:
+
...
10. Hydrogen peroxide is the common name for H2O2 and has many uses from disinfecting wounds to paper
production. Draw a model representing 3 hydrogen peroxide breaking down into hydrogen gas and
oxygen gas
Chemical equation: 3H2O2. . 3H2 +. 3O2
Models:
+.
Objective 4 14
Objective 4 15
3A
A sodium ion is positively charged while a chlorine ion is negatively charged. Since different charges are
attracted to each other (much like magnets), they will combine to form NaCl (which is table salt). This
combining due to opposite charges is an ionic bond resulting in an ionic compound.
Objective 4 16
Three Fluorine and
two Chlorine atoms M F3Cl2 trifluorine dichloride
5
3D
Chemical Formula Li + ScP Li3P + Sc
Word equation lithium scandium phosphoride lithium phosphoride scandium
Model
+ +
Chemical Formula H2 + O2 H2O2
Word equation Hydrogen gas + Oxygen gas dihydrogen dioxide
Objective 4 17
Model
+
Chemical Formula Fe + O2 Fe2O3
Word equation iron + oxygen gas iron (III) oxide
Model
+
1. W rite the word equation for this chemical reaction: Fe + F FeF2
Iron + Fluorine iron (II) fluoride
H20 NaCl O2 ClN O MgF2 C6H12O6