Download Balancing Chemical Equations

Balancing Chemical Equations
PART I:
Background Information: Word and Formula Equations
The first step in writing a chemical equation is to identify the facts to be represented. It is
helpful to write a word equation, an equation in which the reactants (left) and products (right) in
a chemical reaction are represented by words. A word equation has only qualitative (descriptive)
meaning. It does not give the whole story because it does not give the quantities of reactants
used or products formed. A formula equation represents the reactants (left) and products (right)
of a chemical reaction by their symbols or formulas. Chemical formulas must be written
correctly according to the rules of nomenclature.
Word Equation (A)
An aqueous solution of hydrochloric acid reacts with an aqueous solution of sodium hydroxide
to produce liquid water and aqueous sodium chloride.
Formula Equation (A)
HCl (aq)
+ NaOH (aq) H2O (l) + NaCl (aq)
Word Equation (B)
Solid calcium carbonate decomposes when heated to yield solid calcium oxide and carbon
dioxide gas.
Formula Equation (B)
CaCO3 (s)
CaO (s) + CO2 (g)
Word Equation (C)
Gaseous ethene and gaseous hydrogen will react in the presence of a platinum catalyst to form
ethane gas.
Formula Equation (C)
C2H4 (g)
+ H2 (g)
Pt
C2H6 (g)
Group Activity:
1. What does the arrow represent in a chemical equation?
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
2. What do the following symbols in the equations above represent?
(s)
(l)
(g)
(aq)
Pt
3. In the table below, indicate the reactant(s) and product(s) for each of the equations above.
EQUATION
REACTANTS
Name
Formula
Name
PRODUCTS
Formula
A
B
C
4. In chemical equation (C), is platinum a reactant, a product, or neither? Explain.
Model: Atoms Are Conserved in Chemical Reactions.
Chemical reactions are described by chemical equations. According to the Law of Conservation
of Mass (Matter), atoms are neither created nor destroyed when chemical reactions take place.
Therefore, the number of atoms of each element must be identical on the reactant (left) and the
product (right) sides of a balanced chemical reaction.
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
Reaction (D)
CuO (s) +
H2(g)
CO(g)
+
Cu(s)
+
Reaction (E)
O2(g)
+
H2O(g)
+
CO2(g)
+
Group Activity:
5. How many of each type of atom are represented on each side of the equation in reaction (D)?
Cu
O
H
Reactant
Side
Product
Side
6. Does this equation (D) obey the Law of Conservation of Mass (Matter)? Explain.
7. How many of each type of atom are represented on each side of the equation in reaction (E)?
C
O
Reactant
Side
Product
Side
8. Does this equation (E) obey the Law of Conservation of Mass (Matter)? Explain.
9. If either Reaction D or E does not obey the Law of Conservation of Mass (Matter), draw
additional molecules on the reactant and/or product side in order to make the number of all
atoms equal on both sides of the equation. (Remember that once written correctly, chemical
formulas cannot be changed. In other words, molecules must remain intact.)
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
10. In reaction (D), how many H2O molecules are produced for every H2 molecule that is
consumed?
11. In reaction (E), how many CO2 molecules are produced for every O2 molecule consumed?
12. In reaction (E), how many CO molecules react with every O2 molecule?
Independent Activity:
1. Read pages 243 through 248.
2. Write word and formula equations for the chemical reaction that occurs when solid sodium
oxide is added to water at room temperature and forms sodium hydroxide (dissolved in the
water). Include symbols for physical states in the formula equation.
3. Translate the following chemical equation into a sentence:
PbCl2(aq) + Na2CrO4(aq) PbCrO4(s) + NaCl(aq)
4. Work problems 18 and 19 on page 270.
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
Balancing Chemical Equations
PART II:
Background Information: Balanced Chemical Equations
A balanced chemical equation represents a chemical reaction that obeys the Law of
Conservation of Mass (Matter). It can be thought of as describing how many atoms or molecules
of reactants are consumed in order to produce a certain number of atoms or molecules of
products. A coefficient is a small whole number that appears in front of a formula in a chemical
equation. The coefficient represents the relative number of atoms or molecules.
Recall from Part I of this activity the following reactions:
Reaction (D)
CuO (s) +
H2(g)
CO(g)
+
O2(g)
+
Cu(s)
+
Reaction (E)
+
H2O(g)
+
CO2(g)
In order to answer question 9, Reaction D was already drawn correctly, but Reaction E should
have been redrawn as pictured below:
+
This picture shows 2 carbon atoms and 4 oxygen atoms on each side of the equation. These
atoms are represented as 2 CO molecules and 1 O2 molecule on the reactant side and 2 CO2
molecules on the product side of the equation.
Group Activity:
1. Based on the correct drawings write a formula equation that will obey the Law of
Conservation of Mass (Matter) for both Reaction D and E. In order to do this, coefficients
may be required.
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
2. Is the number of molecules identical on the reactant and product sides of both of these
balanced equations?
3. Explain how your answer to # 2 can be consistent with the idea that atoms are neither created
nor destroyed when chemical reactions take place.
4. Why must we balance chemical equations?
Model: Balanced Chemical Equations
a) Zn (s) + 2 HCl (aq) H2 (g) + ZnCl2 (aq)
b) 2 H2 (g) + O2 (g) 2 H2O (g)
c) BaCl2 (aq) + 2 AgNO3 (aq) Ba(NO3)2 (aq) + 2 AgCl (s)
d) 2 C6H14 (g) + 19 O2 (g) 12 CO2 (g)
+ 14 H2O (g)
Group Activity:
5. What is the coefficient for hydrochloric acid in equation a?
6. What is the coefficient for barium nitrate in equation c?
7. How many barium nitrates are on the product side of equation c? Does your answer agree
with your answer for # 6 above?
8. How many barium atoms are on each side of equation c? Explain how you arrived at this
answer.
9. How many carbon atoms are on each side of equation d? Explain how you arrived at this
answer.
10. How many oxygen atoms are on each side of equation d? Explain how you arrived at this
answer.
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
11. Balance the following chemical equations:
a) ______Cr(s) + ______S8(s)
b) ______NaHCO3 (s)
______Cr2S3(s)
______Na2CO3 (s) + ______CO2(g) + ______H2O (g)
c) ______Fe2S3 (s) + ______HCl (g)
______FeCl3 (s) + ______H2S (g)
d) ______CS2 (l) + ______NH3 (g)
______H2S (g) + ______NH4SCN (s)
e) ______Fe2(SO4)3 (aq) + _____KOH (aq) ______K2SO4 (aq) + ______Fe(OH)3 (s)
f) ______C25H52 (l)
+
______O2 (g) ______CO2(g) + ______H2O (g)
12. The trial-and-error method for balancing equations can be successful; however it can be
made easier by following some simple guidelines. Develop a few simple guidelines to
achieve a balanced chemical equation.
13. Use your guidelines to balance the following chemical equations:
a) _____H3PO4 _____H4P2O7 + _____H2O
b) _____C6H6
+ _____O2 _____CO2 + _____H2O
c) _____Al(OH)3 + _____H2SO4 _____Al2(SO4)3 + _____H2O
14. What adjustments, if any, need to be made to your guidelines in order to balance the
equations above?
Independent Activity:
15. Read pages 250 through 254. Carefully study the sample problems 8.3, 8.4, and 8.5 on pages
252 – 254.
16. Work practice problem on page 254.
17. Write the balanced chemical equation for the gaseous reaction of methane (CH4) with oxygen
(O2) to form carbon dioxide (CO2) and water (H2O).
18. Chapter 8: page 270, questions #20 and #21.
19. Chapter 8: page 272, questions #41 and #47.
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
Balancing Chemical Equations
Teacher Notes
Time Required:
Estimated 20-30 minutes for Part I and 50 minutes for Part II. It is suggested that Part I and Part
II be completed on consecutive days.
Prerequisites:
Chemical formulas and nomenclature
Learning Objectives:
1.
2.
3.
4.
Write word equations correctly.
Write formula equations correctly, using proper symbolic notation.
Correctly balance chemical equations.
Explain how a balanced chemical equation illustrates the Law of Conservation of Mass
(Matter).
Considerations:
This activity is a wonderful way to introduce the concept of writing and balancing
chemical equations.
Be careful not to answer the students’ questions for them. If a group asks a question
concerning content, rather than supplying the answer, ask a question in return that will steer them
toward discovering the answer for themselves. Another way to intervene with the group may be
to have the Spokesperson or Presenter for the group to restate their reasoning so that they have
the opportunity to pinpoint misconceptions or faulty reasoning on their own.
Closure:
It is always good to have the students reflect on what they have learned before leaving
class. One way to do this is to stop the activity about 5 minutes before the end of class and have
students take out a sheet of paper. Have them record one thing that they learned as a result of the
lesson that day. Then have them to ask a question concerning the lesson. The question could be
something that is still unclear to them or it could be something they are curious about or a subject
that they think may be related to the lesson.
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
Answers to Questions in Group Activity:
Part I:
1. What does the arrow represent in a chemical equation? Yields or produces
2. What do the following symbols in the equations above represent?
(s)
solid
(l)
liquid
(g)
gas
(aq)
aqueous
heat
Pt
platinum catalyst
3. In the table below, indicate the reactant(s) and product(s) for each of the equations above.
EQUATION
A
B
C
REACTANTS
Name
Formula
Name
PRODUCTS
Formula
hydrochloric acid
HCl
water
H2O
sodium hydroxide
NaOH
sodium chloride
NaCl
calcium
carbonate
CaCO3
calcium oxide
CaO
carbon dioxide
CO2
ethane
C2H6
ethene
C2H4
hydrogen
H2
4. In chemical equation (C), is platinum a reactant, a product, or neither? Explain.
Neither, because it is not on either side of the arrow.
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
5. How many of each type of atom are represented on each side of the equation in reaction (D)?
Reactant
Side
Product
Side
Cu
1
O
1
H
2
1
1
2
6. Does this equation (D) obey the Law of Conservation of Mass (Matter)? Explain.
Yes, because there are the same number of each atom on both sides of the equation.
7. How many of each type of atom are represented on each side of the equation in reaction (E)?
Reactant
Side
Product
Side
C
1
O
3
1
2
8. Does this equation (E) obey the Law of Conservation of Mass (Matter)? Explain.
No, because there are NOT the same number of oxygen atoms on each side of the equation.
9. If either Reaction D or E does not obey the Law of Conservation of Mass (Matter), draw
additional molecules on the reactant and/or product side in order to make the number of all
atoms equal on both sides of the equation. (Remember that once written correctly, chemical
formulas cannot be changed. In other words, molecules must remain intact.)
+
10. In reaction (D), how many H2O molecules are produced for every H2 molecule that is
consumed?
one
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
11. In reaction (E), how many CO2 molecules are produced for every O2 molecule consumed?
two
12. In reaction (E), how many CO molecules react with every O2 molecule?
two
Part II
1. Based on the correct drawings write a formula equation that will obey the Law of
Conservation of Mass (Matter) for both Reaction D and E. In order to do this, coefficients
may be required.
(D) CuO (s) +
H2(g)
(E) 2 CO(g)
+
Cu(s)
O2(g)
+
H2O(g) already balanced
2 CO2(g)
2. Is the number of molecules identical on the reactant and product sides of both of these
balanced equations?
No!!!!!!! NOTE: This question asks about molecules, not atoms. In reaction (D), there are 2
molecules on the reactant side and 1 atom and 1 molecule on the product side. In reaction (E),
there are 3 molecules on the reactant side and 2 molecules on the product side. If your students
do not see this, hint that they look back at their picture from part I.
3. Explain how your answer to # 2 can be consistent with the idea that atoms are neither created
nor destroyed when chemical reactions take place.
Because the atoms are balanced, even though the molecules are not.
4. Why must we balance chemical equations?
In order to obey the Law of Conservation of Mass (Matter).
5. What is the coefficient for hydrochloric acid in equation a? 2
6. What is the coefficient for barium nitrate in equation c? 1
7. How many barium nitrates are on the product side of equation c? Does your answer agree
with your answer for # 6 above? 1, yes
8. How many barium atoms are on each side of equation c? Explain how you arrived at this
answer. 1, because there is 1 Ba in BaCl2 and 1 Ba in Ba(NO3)2
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
9. How many carbon atoms are on each side of equation d? Explain how you arrived at this
answer. 12, because there are 2 molecules of C6H14 and 12 molecules of CO2
10. How many oxygen atoms are on each side of equation d? Explain how you arrived at this
answer. 38, because there are 19 molecules of O2, 12 molecules of CO2 = 24 atoms of O, and
14 molecules of H2O = 14 atoms of O
11. Balance the following chemical equations:
a) ___16___Cr(s) + ___3___S8(s) b) ____2__NaHCO3 (s)
___8___Cr2S3(s)
______Na2CO3 (s) + ______CO2 (g) + ______H2O (g)
c) ______Fe2S3 (s) + ____6__HCl (g)
__2____FeCl3 (s) + ___3___H2S (g)
d) ______CS2 (l) + ___2___NH3 (g)
______H2S (g) + ______NH4SCN (s)
e) ______Fe2(SO4)3 (aq) + __6__KOH (aq) ___3__K2SO4 (aq) + __2___Fe(OH)3 (s)
f) ______C25H52 (l)
+
___38___O2 (g) __25____CO2(g) + ___26___H2O (g)
12. The trial-and-error method for balancing equations can be successful; however it can be
made easier by following some simple guidelines. Develop a few simple guidelines to
achieve a balanced chemical equation.
Student answers may vary. 13. Use your guidelines to balance the following chemical equations:
a) __2__H3PO4 _____H4P2O7 + _____H2O
b) ___2__C6H6
+ ___15__O2 ___12__CO2 + __6___H2O
c) ___2__Al(OH)3 + ___3__H2SO4 _____Al2(SO4)3 + ___6__H2O
14. What adjustments, if any, need to be made to your guidelines in order to balance the
equations above?
Student answers may vary. However, the purpose of this question is to show students that there
are a few helpful guidelines to use when balancing equations:
• Save H and O for last.
• Keep polyatomic ions together when possible (treat them as a unit).
• Combustion reactions may require doubling to remove fractions from the coefficients.
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
Can A Molecule Be Identified by its Percent Composition?
Background Information: Percent Composition
The percent composition (by mass) of an element in a molecule is the mass of the
element in the molecule divided by the mass of the entire molecule times 100. Or, because the
number of atoms (molecules) is proportional to the number of moles of atoms (molecules),
Percent composition of element x = mass of x in one mole of the compound x 100
Mass of one mole of the compound
% Ba in BaCl 2 = mass of Ba in 1 mole of BaCl 2 x 100
mass of 1 mole of BaCl 2
% Ba in BaCl2 =
137.3 grams Ba
208.3 grams BaCl2
x 100 = 65.91% Ba in BaCl2
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
Group Activity
1. Fill in the missing molecular formulas using the structural formulas in Table 1.
2. Find the % composition of benzene, cyclobutane, and 1-octene.
3. Verify that the % composition given for ethyne in Table in Table 1 is correct.
4. Is it possible, given the original data in Table 1, to determine the % composition by mass of
H for 2-butene without using the equation given in the model above? If so, how?
5. Based on the data in Table 1, is it possible to determine the molecular formula of a
compound solely from its percent composition? Why or why not?
6. What is similar about the molecular formulas of cyclobutane and 1-octene?
7. Compare the molecular formulas of ethyne and benzene?
8. What mathematical relationship do all compounds with the same % composition have?
Background Information: Empirical Formula
The empirical formula of a compound describes the relative number of each type of atom in
the compound. It is given in terms of the smallest-possible-whole-number ratios (as subscripts).
For example, the empirical formula of ethane is CH3. (Note that the subscript “1” is omitted.)
Group Activity
9. Write the empirical formulas for all of the compounds in Table 1.
Independent Activity
1. The molecule 2-hexene has the molecular formula C6H12. Refer to Table 1 and determine the
percent composition of H in the molecule.
2. Determine the percent composition of each element in acetic acid, CH3COOH.
3. A molecule containing only nitrogen and oxygen, contains 30.4% N by mass.
(a) How many grams of N would be found in a 100.0 g sample of the compound?
(b) How many grams of O would be found in the same sample of the compound?
(c) How many moles of N would be found in a 100.0 g sample?
(d) How many moles of O would be found in the same sample?
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
(e) What is the ratio of number of moles of O to number of moles of N?
(f) What is the empirical formula of the compound?
4. An unknown liquid contains 38.7% C and 51.6% O by mass. The remainder of the
compound is H. What is the empirical formula?
5. Holt, Rinehart, Winston 2002 Text. Chapter 7,p. 229 - 231 practice problems 1-3, p. 231; p.
232-233, practice problems 1 and 2 and section review problems 1-5, p. 233; p. 237 problems
36-39, 47, 50, and 52.
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
Limiting Reagent (Reactant)
Model 1: The S’more
A delicious treat known as a S’more is constructed with the following ingredients and amounts:
2 graham crackers
1 chocolate bar
2 marshmallows
At a particular store, these items can be obtained only in full boxes, each of which contains one
gross (144) of items. A gross is a specific number of items, analogous (but not equal) to one
dozen. The boxes of items have the following net weights ( the weight of the material inside the
box):
Box of graham crackers
Box of chocolate bars
Box of marshmallows
9.0 pounds
36.0 pounds
3.0 pounds
Group Activity
1. Based on the information given, which of the three ingredients (a graham cracker, a
chocolate bar, or a marshmallow) weighs the most? Which weighs the least?
2. If you have a collection of 100 graham crackers, how many chocolate bars and how many
marshmallows do you need to make S’mores with all of the graham crackers?
3. If you have a collection of 1000 graham crackers, 1000 chocolate bars, and 1000
marshmallows, how many S’mores can you make? What will be left over?
4. If you have 36.0 pounds of graham crackers, 36.0 pounds of chocolate bars, and 36.0 pounds
of marshmallows, which item do you have the most of? The least? Explain your reasoning
5. a) If you attempt to make S’mores from the material described in question #4, what item
will you run out of first? (This item is known to chemists as the limiting reagent
because it is the reactant which limits the amount of product which can be made.)
b) How many gross of S’mores will you have made?
c) How many gross of each of the two left over items will you have?
d) How many pounds of each of the left over items will you have?
e) How many pounds of S’mores will you have?
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
6. Using G as the symbol for graham crackers and Ch as the symbol for the chocolate bars and
M for marshmallows, write a “balanced chemical equation” for the production of S’mores.
7. Why is it not correct to state that if we start with 36 pounds each of G, Ch, and M, then we
should end up with 3 x 36 = 108 pounds of S’mores?
Model 2: Water
8.
25.0 grams of hydrogen and 25.0 grams of oxygen react to form water.
a) Write the balanced chemical equation and show all steps.
b) Assuming that the reaction goes to completion, which element will be totally consumed
in the formation of water?
c) What is the limiting reagent?
d) How many grams water can be produced?
e) How many grams of the excess element remain unreacted?
Independent Activity #1
Read p. 288-292 Modern Chemistry Text
1. Given the balanced chemical equation: 2 NO(g) + O2(g) 2 NO2(g)
calculate the mass of nitrogen dioxide that can be made from 30 grams of NO and 30 grams
of O2.
2. Zinc and iodine, I2, react to form zinc iodide, ZnI2 (the reactants and the product are all solids
at room temperature).
a) Write a balanced chemical equation for this reaction.
b) Suppose that 50.0 g of zinc and 50.0 g of iodine are used to form zinc iodide.
1) Assuming that the reaction goes to completion, which element will be totally
consumed in the formation of the zinc iodide?
2) What is the limiting reagent?
3) How many grams of zinc iodine can be produced?
4) How many grams of the excess element remain unreacted?
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
3. Acetylene gas, HCCH, is commonly used in high temperature torches.
a) Write a balanced chemical equation for the reaction of acetylene with hydrogen gas (H2)
to form ethane (C2H6).
b) How many grams of ethane can be produced from a mixture of 30.3 grams of HCCH and
4.14 grams of H2?
4. Titanium (Ti) is a strong, lightweight metal that is used in the construction of rockets, jet
engines, and bicycles. It can be prepared by reacting TiCl4 with Mg metal at very high
temperatures. The products are Ti(s) and MgCl2(s).
a) Provide a balanced chemical reaction for the reaction described above.
b) How many grams of Ti metal can be produced from a reaction involving 3.54 x 104 g of
TiCl4 and 6.53 x 103 g of Mg?
Independent Activity #2
1.
Modern Chemistry Text - Page 297, problems 22 27
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
EUREKA ! ! !
(Seeing the unseen)
Why: An understanding of atomic structure is foundational to the understanding of chemical
principles. This activity will help cultivate an understanding of the development of
currently accepted models of atomic structure as well as an appreciation of the difficulty
of studying the structure of something not directly observable.
Introductory Activity:
Distribute the Obsertainers available from Science in Motion.
Group Work:
1)
Devise a procedure for determining the plastic shape embedded in the Obsertainer:
NO OPENING OF CONTAINERS
2)
Perform the procedure.
3)
Draw the plastic shape that your group determined experimentally in the circle below.
4)
Would you revise your original procedure?
5)
Open the Obsertainer to determine the shape inside. How accurate were you at
determining the shape?
6)
How would you describe the process you followed in order to determine the hidden
shape inside the Obsertainer?
7)
What would you name the process scientists use to investigate items that cannot be
seen?
How?
Developed by Alabama Science in Motion teachers at the 2003 summer workshop.
Page 1
Revised 8/2/2005
Model:
Results of experiment:
21000 positively charged particles were shot at the foil.
20996 positively charged particles landed in region A.
3 positively charged particles landed in region B.
1 positively charged particle landed in region C.
8)
Calculate the percentage of particles that landed in each region to complete the table
below.
Percentage
Region A
Region B
Region C
9)
In what region did the majority of the particles land?
10)
What interaction had to happen between these particles and the gold atoms within the
foil in order to explain this result?
Developed by Alabama Science in Motion teachers at the 2003 summer workshop.
Page 2
Revised 8/2/2005
11)
Describe the interaction that occurred between the positive particles that landed in
Region B and the gold atoms in the foil in order to account for the results.
12)
Describe the interaction that occurred between the positive particles that landed in
Region C and the gold atoms in the foil in order to account for the results.
13)
Carefully consider your results for several years like Ernest Rutherford did in the
early 1900s. (Just kidding, but that is really what he did!)
14)
Write a hypothesis of the structure of an atom based on your results. Draw a picture
to illustrate your hypothesis.
Individual Activity (Homework):
15)
Read pages _______ in your textbook.
16)
Compare your group’s reasoning process and results with that of Ernest Rutherford
and his colleagues. Critique your group’s answer to question #14 and revise it (if
necessary) to more closely follow the model proposed by Rutherford.
Developed by Alabama Science in Motion teachers at the 2003 summer workshop.
Page 3
Revised 8/2/2005
EUREKA ! ! !
(Seeing the unseen)
Teacher Notes
Time Required:
One 50 minute class period.
Prerequisites:
Students should understand that like-charged particles repel each other.
They must know this in order to reason through the particle behavior that
leads to the invention of the concept.
Learning Objectives:
1. Understand the observational and logic skills necessary for performing indirect
measurements.
2. Explain currently accepted models of atomic structure.
Performance Criteria:
1.
2.
3.
4.
Explain the process for performing indirect observations and measurements.
Interpret the results of observed phenomena and collected quantitative data.
Describe the currently accepted model of atomic structure.
Explain the objective observations that led to the development of current atomic structure
models.
Considerations:
High school students are in the midst of developing abstract thinking skills so your
classes will probably contain students at varying levels of skill in this area. Be VERY
CAREFUL not to rob them of this opportunity to expand their skills by supplying them with too
much information and too many answers. You will probably find that students are easily
frustrated with this activity because it stretches their reasoning abilities but this is an excellent
way for them to expand their capacity for applying abstract reasoning and logic.
If you find that some groups seem to hit a “dead end” you may want to try having some
arbitrary group member rotate within the groups. It is probably best to leave the Manager and
Recorder in the group where they began, but the Spokesperson/Presenter or Technician/Reflector
would be a good one to rotate. Just have all the Presenters rotate clockwise (or whatever scheme
you choose). This may bring some fresh blood and new understanding to a stagnant group.
Sometimes just through re-explaining to the new group member what has been done and said
within the group, the rehashing spurs new ideas. Also the new group member may bring new
ideas from the discussions of the group they just left.
Developed by Alabama Science in Motion teachers at the 2003 summer workshop.
Page 4
Revised 8/2/2005
Closure:
It is always good to have the students reflect on what they have learned before leaving
class. One way to do this is to stop the activity about 5 minutes before the end of class and have
students take out a sheet of paper. Have them record one thing that they learned as a result of the
lesson that day. Then have them to ask a question concerning the lesson. The question could be
something that is still unclear to them or it could be something they are curious about or a subject
that they think may be related to the lesson.
Answers to Questions:
Answers will vary in the group work depending on the container assigned to the group and
students approach to solving the problem
8. Region A = 99.981 %
Region B = 0.014 %
Region C = 0.005%
9. Region A
10. There would have been no interaction between the alpha particles and the gold atoms.
11. The positive alpha particles must have come close to another positively charged particle
in order to be slightly deflected off course.
12. The positive alpha particles must have collided directly with positive particles of the gold
atoms in order to have bounced back toward the source of the alpha particles.
13.
14. Answers will vary – Rutherford concluded that the atom was mostly space but did
contain a dense region of positive charge.
Developed by Alabama Science in Motion teachers at the 2003 summer workshop.
Page 5
Revised 8/2/2005
LABORATORY SAFETY
(How can we all survive chemistry labs?)
Why: The chemistry laboratory is a potentially hazardous place to work. There are
dangerous substances and equipment that must be handled with care. This exercise is
designed to construct student knowledge of common lab safety issues. and to focus on
the importance of laboratory safety and the procedures to execute before, during, and
after laboratory activities.
Group Members
Group Activity
1. Brainstorm as many lab safety rules as you can within your group (time limit 5 minutes).
2. Determine the top five safety rules from the list generated by your group and rank them
in order of importance.
3. Your instructor will supply you with a random list of lab safety rules. Rank these safety
rules in order of decreasing importance (most important to least important).
4. Place an asterisk beside the top five rules identified by your group in question 2 that
appear on the instructor’s list.
5. Compare your group’s brainstormed list to the instructor’s list. Account for any
differences that you find.
Developed by Alabama Science in Motion teachers Summer, 2003.
Page 1
Revised 8/2/2005
6. Design an emergency procedure to use in the event of each of the situations listed below
in which the instructor is incapacitated (unconscious) and students have to react
responsibly to the situation to reduce injury and panic.
•
A chemical table or floor fire
•
An individual’s clothing catches on fire
•
A cut or a burn injury
•
An eye injury
•
An acid spill
•
A base spill
•
A gas or noxious fumes
Developed by Alabama Science in Motion teachers Summer, 2003.
Page 2
Revised 8/2/2005
7. Identify these safety symbols and determine their proper location in your school lab.
Floor Plan:
In the space below draw a sketch of the floor plan of your school’s
chemistry laboratory. There should be 2 exits from your lab. (NOTE:
Sometimes a window is considered an alternative exit.) Locate both exits
on your floor plan and label where the safety goggles, safety shower, eye
wash station, and fire extinguisher are located.
Developed by Alabama Science in Motion teachers Summer, 2003.
Page 3
Revised 8/2/2005
Review Activity
Each group will choose one of the safety procedures and create a laboratory safety poster
for display in the classroom.
Developed by Alabama Science in Motion teachers Summer, 2003.
Page 4
Revised 8/2/2005
Instructor’s Safety List
Acids should be transferred to water only (never add water to acid).
Aprons must be worn at all times.
Bunsen burners should be monitored at all times.
Chemicals must be transferred from large stock bottles to small manageable containers.
Fire blankets should be used on individuals in case of fire.
Fire extinguishers should not be used on individuals.
Broken glassware should be disposed of in its proper container.
Goggles must be worn at all times.
Long hair should be tied back.
Loose clothing should not be worn.
No eating or drinking in the laboratory.
No horseplay in the laboratory.
Open-toed shoes should not be worn.
Solid substances should not be disposed of in the sink unless approved by your instructor.
Unlabeled glassware with unknown substances should not be used.
Developed by Alabama Science in Motion teachers Summer, 2003.
Page 5
Revised 8/2/2005
The Mole Concept
Why: Samples of matter are composed of numerous particles (atoms, ions, or molecules).
Because the numbers of particles are so huge, chemists have established a unit of
measure called the mole (abbreviated mol) for use in counting them. In this activity you
will discover the relationship between the term “mole” as it relates to the number of
particles and the mass of the particles.
Model 1:
Below are some equivalent quantities with which you may or may not be familiar:
1 pair of shoes = 2 shoes
1 dozen donuts = 12 donuts
1 ream of copy paper = 500 sheets of copy paper
1 gross of pencils = 144 pencils
One elephant has one trunk and four legs.
Equivalent quantities may be used as conversion factors. A conversion factor is written as a
fraction where the numerator and denominator are expressed in different units but are equal
quantities. For example:
1 ream of copy paper
500 sheets of copy paper
OR
500 sheets of copy paper
1 ream of copy paper
Because the numerator and denominator represent the same thing, only in different units,
conversion factors are always = 1.
Equivalent quantities (conversion factors) used in the study of chemistry:
1 mole of items = 6.022 x 10 23 items (Avogadro’s Number)
(items = atoms, molecules, ions or formula units)
One methane molecule, CH4, contains one carbon atom and four hydrogen atoms.
Key Questions:
If your answer is extremely large or small, use scientific notation form. Include units for all
answers. Show your work.
1.
How many trunks are found in one dozen elephants?
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
Page 1
2.
How many legs are found in one dozen elephants?
3.
How many trunks are found in a ream of elephants?
4.
How many legs are found in a pair of elephants?
5.
How many carbon atoms are found in one dozen methane (CH4) molecules?
6.
How many hydrogen atoms are found in one dozen methane molecules?
7.
How many carbon atoms are found in a pair of methane molecules?
8.
How many hydrogen atoms are found in a ream of methane molecules?
9.
How many elephants are there in one mole of elephants?
10.
How many trunks are found in one-half mole of elephants?
11.
How many legs are found in one mole of elephants?
12.
How many methane molecules are there in one mole of methane?
13.
How many carbon atoms are found in one mole of methane molecules?
14.
How many hydrogen atoms are found in one-half mole of methane molecules?
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
Page 2
Model 2:
The mass of 1 mole of any pure substance = average atomic mass expressed in grams of that
substance. For example:
1.008 amu = average atomic mass for H
1.008 g H = 1 mol H
15.
Where would you find the average atomic mass for carbon?
16.
What is the average mass (in amu) of one carbon atom?
17.
What is the mass (in grams) of one mole of carbon atoms?
18.
What is the average mass (in amu) of one methane molecule?
19.
What is the mass (in grams) of one mole of methane molecules?
20.
How is the mass in amu of one atom of an element related to the mass in grams of one
mole of that element?
21.
Refer to questions #12 and 19. If you measured out the mass of methane in your
response to question 19, how many methane molecules would you have?
22.
If you measure out 58.69 g of Ni, how many nickel atoms would you have?
23.
If you want to measure out 3.011 x 1023 atoms of gold, how many grams would you need
to measure out?
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
Page 3
Complete the Table below by supplying the necessary information.
Substance
Number of Particles
Al
6.022 x 1023 atoms
H2O
O2
Mass in grams
18.02 g
1.505 x 1023 molecules
Ne
10.09g
Skill Development Exercises:
1.
Indicate whether each of the following statements is true or false and explain your
reasoning.
A. One mole of NH3 weighs more than one mole of H2O.
B. There are more carbon atoms in 48 grams of CO2 than in 12 grams of diamond (a
form of pure carbon).
C. There are equal numbers of nitrogen atoms in one mole of NH3 and one mole of N2.
D. The number of Cu atoms in 100 grams of Cu(s) is the same as the number of Cu
atoms in 100 grams of copper (II) oxide, CuO.
E. The number of Ni atoms in 100 moles of Ni(s) is the same as the number of Ni atoms
in 100 moles of nickel (II) chloride, NiCl2.
F. There are more hydrogen atoms in 2 moles of NH3 than in 2 moles of CH4.
2.
Use grammatically correct sentences to describe how to calculate the number of H atoms
in any number of moles of NH3.
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
Page 4
The Mole Concept
Teacher Notes
Time Required:
One 50 minute class period.
Prerequisites:
Knowledge of average atomic mass, the use of the Periodic Table to find an element’s average
atomic mass, and the calculation of a formula mass
Learning Objectives:
1.
2.
3.
Understand the relationship between the unit “mole” and Avogadro’s number.
Define the gram formula mass of a substance.
Understand the relationship between the mole and the gram formula mass.
Performance Criteria:
1.
Perform conversions between mass, moles, and numbers of particles.
Considerations:
This activity is a wonderful way to introduce the concept of moles to an introductory
chemistry class. No previous knowledge of moles is required.
Be careful not to answer the students’ questions for them. If a group asks a question
concerning content, rather than supplying the answer, ask a question in return that will steer them
toward discovering the answer for themselves. Another way to intervene with the group may be
to have the Spokesperson or Presenter for the group to restate their reasoning so that they have
the opportunity to pinpoint misconceptions or faulty reasoning on their own.
Closure:
It is always good to have the students reflect on what they have learned before leaving
class. One way to do this is to stop the activity about 5 minutes before the end of class and have
students take out a sheet of paper. Have them record one thing that they learned as a result of the
lesson that day. Then have them to ask a question concerning the lesson. The question could be
something that is still unclear to them or it could be something they are curious about or a subject
that they think may be related to the lesson.
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
Page 5
Answers to Questions:
Model 1 – Key Questions:
1. 12 trunks
2. 48 legs
3. 500 trunks
4. 8 legs
5. 12 carbon atoms
6. 48 hydrogen atoms
7. 2 carbon atoms
8. 2000 hydrogen atoms
9. 6.022 x 1023 elephants
10. 3.011 x 1023 trunks
11. 2.409 x 1024 legs
12. 6.022 x 1023 molecules
13. 6.022 x 1023 carbon atoms
14. 1.204 x 1024 hydrogen atoms
Model 2
15. periodic table
16. 12.01 amu
17. 12.01 g
18. 16.05 amu
19. 16.05 g
20. One atomic mass unit (amu) equals the mass in grams of one mole of an element.
21. 6.022 x 1023 molecules
22. 6.022 x 1023 atoms
23. 98.99 g
Substance
Number of Particles
Mass in grams
Al
6.022 x 1023 atoms
26.98 g
H2O
6.022 x 1023 molecules
18.02 g
O2
1.505 x 1023 molecules
8.00 g
Ne
3.011 x 1023 atoms
10.09g
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
Page 6
Skill Development Exercises:
1.
a. False, NH3 1 mole = 17.03 g, H2O 1 mole = 18.02 g
b. True, there are 6.57 x 1023 atoms of carbon in 48 g of CO2 and only 6.016 x 1023 atoms of
carbon in 12 g of diamond
c. False, 1 mole of NH3 = 6.022 x 1023 atoms of nitrogen, 1 mole of N2 = 1.2044 x 1024 atoms of
nitrogen
d. False, 100 g of Cu = 7.57 x 1023 atoms of copper, 100 g of CuO = 9.48 x 1023 atoms of
copper
e. True, Since 1 molecule of NiCl2 contains 1 atom of nickel then 1 mole of NiCl2 would
contain 6.022 x 1023 atoms of nickel. One mole of nickel also contains 6.022 1023 atoms
of nickel.
f. False, In 2 moles of NH3 there are 3.61 x 1024 hydrogen atoms but in 2 moles of CH4 there are
4.82 x 1024 hydrogen atoms.
2.
In one molecule of NH3 there are three atoms of hydrogen and in mole of NH3 there are
6.022 x1023 molecules of NH3. To determine the number of hydrogen atoms in any number of
moles, multiply the number of moles by 6.022 x 1023 to convert to molecules. Then convert
molecules to atoms by multiplying by three.
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
Page 7
1
What is an Atom?
Background Information:
An atom is defined as the smallest particle of an element that retains the chemical properties of
that element. All atoms are composed of the same basic particles, but all atoms are not the same.
The Periodic Table is a useful tool for determining the number of particles in different atoms.
Here is the Periodic Table entry for the element carbon:
6
C
12.011
Atomic number
Atomic symbol
Atomic mass
Model: Schematic Diagrams for Various Atoms and Ions
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
2
Group Members:
Group Activity:
1. How many protons are found in 12C? 13C? 13C-?
2. How many neutrons are found in 12C? 13C? 13C-?
3. How many electrons are found in 12C? 13C? 13C-?
4. Based on the background information,
a) what do all carbon atoms (and ions) have in common?
b) what do all hydrogen atoms (and ions) have in common?
5. Look at the Periodic Table provided. The atomic number (normally referred to as Z) is
the number given above each element’s symbol. What is the significance of this atomic
number?
6. What do all nickel (Ni) atoms have in common? (refer to the periodic table if needed)
7. How is the mass number (normally referred to as A) of an atom (or ion) determined?
(NOTE: The mass number is the superscript number to the left of the atomic symbol.)
8. What structural feature is different in isotopes of a particular element?
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
3
Model: Schematic Diagram of Various Atomic Changes
Loss of electrons
Neutral
Atom
Gain of electrons
Change in atomic mass (or neutrons)
Positive
Ion
Negative
Ion
Isotope
9. a) What distinguishes a neutral atom from an ion?
b) How is the charge on an ion determined?
10. Where is most of the mass of a neutral atom, ion and isotope found? Within the nucleus
or outside of the nucleus? Explain your reasoning.
11. What is the mass (in grams) of one 1H atom? Of one 12C atom?
Review Questions/Problems (Individual Effort):
1. Read pages 75-82 in your textbook.
2. Study Sample Problem 3.1 on page 77. Review Practice Problems on page 78.
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
4
3. Complete the following table:
ISOTOPE
31
18
P
ATOMIC
NUMBER
15
O
Ni2+
14
58
NUMBER OF
ELECTRONS
8
19
58
ATOMIC
MASS
39
18
58
27
59
25
3
7
3
3
6
3
N
Zn2+
19 -
F
4. How many electrons, protons and neutrons are found in each of the following?
a)
24
Mg
b)
23
Na+
c)
35
Cl
d)
35
Cl-
e)
56
Fe3+
f)
15
N
g)
16
O2+
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
5
h)
27
Al3+
5. What is the mass (in grams) of 4.35 x 106 atoms of 12C?
6. a) Define atomic mass (A). b) Define atomic number (Z).
Sources:
1. Davis, Raymond E., et al, Modern Chemistry, Holt, Rinehart and Winston, 2002, pages
75-82.
2. Farrell, John J. and Moog, Richard S., Chemistry: A Guided Inquiry, John Wiley & Sons,
1999, pages 1-4.
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
6
What is an Atom?
Teacher Notes
Time Required:
One 50 minute class period.
Prerequisites:
Knowledge of basic dimensional analysis, calculation of unit conversions
Learning Objectives:
1.
2.
3.
Identify the basic subatomic particles.
Understand the relationship between subatomic particles, atomic number, and atomic
mass.
Identify the nucleus of an atom and the subatomic particles contained in it.
Performance Criteria:
1.
Recognize the relationship between the atomic number of an element and its placement
on the Periodic Table.
Considerations:
This activity is a wonderful way to introduce the concept of basic atomic structure. No
previous knowledge of atoms is required.
Be careful not to answer the students’ questions for them. If a group asks a question
concerning content, rather than supplying the answer, ask a question in return that will steer them
toward discovering the answer for themselves. Another way to intervene with the group may be
to have the Spokesperson or Presenter for the group to restate their reasoning so that they have
the opportunity to pinpoint misconceptions or faulty reasoning on their own.
Closure:
It is always good to have the students reflect on what they have learned before leaving
class. One way to do this is to stop the activity about 5 minutes before the end of class and have
students take out a sheet of paper. Have them record one thing that they learned as a result of the
lesson that day. Then have them to ask a question concerning the lesson. The question could be
something that is still unclear to them or it could be something they are curious about or a subject
that they think may be related to the lesson.
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)
7
Answers to Questions in Group Activity:
1.
2.
3.
4.
5.
6.
7.
8.
9.
6, 6, 6
6, 7, 7
6, 6, 7
a) all have 6 protons b) all have 1 proton
It is the same as the number of protons.
They must all have 28 protons.
It is the total of the protons and neutrons.
The number of neutrons is different (which makes the mass different).
a) an ion is charged b) adding the protons (pluses) and electrons (minuses) together
equals the charge
10. inside the nucleus because that is where the protons and neutrons are located. The atomic
masses don’t agree if you add in the electrons that are outside of the nucleus.
11. 1.0078 amu x 1.6606 x 10-24 g = 1.6736 x 10-24 g for the 1H atom
1 amu
12 amu x 1.6606 x 10-24 g = 1.9927 x 10-23 g for the 12C atom
1 amu
Adapted from Chemistry: A Guided Inquiry, 2nd ed. by Moog and Farrell (Wiley and Sons, Inc.)