Name:______________________________________
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Unit 4 —Class Notes Page
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 107 Unit 4 —Class Notes Page
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 108 Name:______________________________________
Veritas:______________________________________
Unit 4, Worksheet 1—
Types of Matter
Read the following information on elements, compounds and mixtures. Fill in the
blanks where necessary.
Elements (pure substances):
1. A pure substance containing only one kind of ____________.
2. An element is always uniform all the way through (homogeneous).
3. An element _____________ be separated into simpler materials (except during
nuclear reactions).
4. Over 100 existing elements are listed and classified on the
____________________.
Compounds (pure substances):
5. A pure substance containing two or more kinds of _______________.
6. A compound is always homogeneous (uniform).
7. Compounds ___________________ be separated by physical means.
Separating a compound requires a _____________________.
8. The properties of a compound are usually different than the properties of the
elements it contains.
Mixtures:
9. Two or more ________________ or _________________ NOT chemically
combined.
10. No reaction between substances.
11. Mixtures can be uniform (called ________________________) and are known as
solutions.
12. Mixtures can also be non-uniform (called ________________________).
13. Mixtures can be separated into their components by chemical or physical
means.
14. The properties of a mixture are similar to the properties of its components.
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 109 Classify each of the following as elements (E), compounds (C) or Mixtures (M). Write
the letter X if it is none of these.
___Diamond (C)
___Sugar (C6H12O6)
___Milk
___Air
___Sulfuric Acid (H2SO4)
___Gasoline
___Krypton (K)
___Bismuth (Bi)
___Uranium (U)
___Ammonia (NH3)
___Salt (NaCl)
___Energy
___Water (H2O)
___Baking Soda (NaHCO3)
___Titanium (Ti)
Match each diagram with its correct description. Diagrams will be used once.
A
B
C
D
E
___1. Pure Element – only one type of atom present.
___2. Mixture of two elements – two types of uncombined atoms present.
___3. Pure compound – only one type of compound present.
___4. Mixture of two compounds – two types of compounds present.
___5. Mixture of a compound and an element.
Identify the following diagrams, using hardware pieces representing particles, as a
pure substance or a mixture. If it is a pure substance, identify it as an element or a
compound. If it is a mixture, identify it as homogenous or heterogeneous.
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 110 Name:______________________________________
Veritas:______________________________________
Unit 4, Worksheet 2—
Separation of Mixtures
1. Identify the separation techniques pictured below. Which technique would be useful to separate a mixture of sand and salt? Of salt and water? 2. Explain why the technique at left would not be effective in separating a mixture
of salt and sugar.
3.
Draw particle representations for the following:
A mixture of iron and sulfur
4.
A compound of iron and sulfur
Explain why a magnet can separate iron atoms from the mixture but not from
the compound.
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 111 5. Consider the four containers below. a. Which of these are mixtures? pure substances? only elements? a. Which of these are mixtures? b. Which contain only compounds? 7. Consider the four containers below. pure substances? only elements 8. pure substances? only elements b. Which contain only compounds? 6. Consider the four containers below. a. Which of these are mixtures? b. Which contain only compounds? Which of the containers in #7 contain a gas? a liquid a solid Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 112 Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 113 Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 114 Name:______________________________________
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Unit 4, Worksheet 3—
Avogadro’s Hypothesis
In Unit 2, you learned that the pressure of a gas is proportional to the Kelvin temperature (P ∝ T), when the volume and number of particles is held constant. Now consider equal volumes of two gases at the same temperature (in the figures below, the sphere in the upper corner of the box is a thermometer bulb). 1. What is reasonable to conclude about the number of gas particles in each container if the pressure and temperature is the same in both containers? Avogadro reached this same conclusion building on the work of Gay-­‐Lussac, who first noted that gases (at the same T and P) reacted in simple integer volume ratios. His hypothesis made it possible to deduce the formulas of compounds formed when these gases react. You have seen evidence that two volumes of hydrogen gas react with one volume of oxygen gas (at the same T and P) to produce water. The conclusion that two molecules of hydrogen combine with one molecule of oxygen to form water works only if we assume that each volume of gas contains the same number of particles. 2. Represent molecules of hydrogen and oxygen in the containers below. React these molecules to form water molecules, leaving no leftover gas. What do the H, O, and 2 in the chemical formula tell us about the composition of water Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 115 3. In like manner, represent particle diagrams that account for the fact that one volume of hydrogen combines with one volume of chlorine to form hydrogen chloride. What do you suppose is the formula of hydrogen chloride? 4. Represent the reaction in which one volume of nitrogen gas reacts with three volumes of hydrogen gas to form ammonia. What is the formula for ammonia? Avogadro built on the work of Gay-­‐Lussac who first noted that gases reacted in simple integer volume ratios (when measured at the same temperature and pressure). Gay-­‐Lussac concluded that this result could be explained if the volumes contained the same number of particles. Chemists found this hypothesis difficult to accept because they reasoned, for example, that if the particles of the gases were combining, then one volume of gas A reacting with one volume of gas B should produce one volume of product. However, it was frequently found that one volume of gas A reacted with one volume of gas B to produce two volumes of product. Chemists, including Gay-­‐Lussac, were unable to account for this behavior of gases. 5. Consider the reaction between hydrogen and chlorine. Two volumes of hydrogen chloride are formed. Sketch particle diagrams consistent with Avogadro’s Hypothesis to represent this reaction. Explain why hydrogen and chlorine molecules that have only one atom each cannot account for the observed behavior. Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 116 Avogadro reasoned that these results could be explained if Gay-­‐Lussac’s particles were actually combinations of smaller particles (which we now call “atoms”). He introduced the use of the term “molecule” to refer to these combinations of smaller particles. “Molecule” comes from “mole” – lumps of matter and “cula” – little. A molecule is a little lump of matter. His hypothesis was consistent with the view that gas pressure is caused by the collisions of molecules with the side of the container. If the pressure is the same, then it seems reasonable that the number of molecules in the container is the same. In addition to the ammonia and hydrogen chloride example combining in a one to one ratio, he found that a number of gases combined in such a way that could only be accounted for if the individual molecules were diatomic. The diagram below shows how one volume of hydrogen reacts with one volume of chlorine to produce two volumes of hydrogen chloride. Making the assumption that the gases are diatomic neatly accounts for the experimental evidence. Suppose that these gases were not diatomic. In the “product containers” combine the atoms of hydrogen and chlorine to make hydrogen chloride. Why is your representation inconsistent with Avogadro’s hypothesis? Of course, Avogadro did not base his hypotheses about number of molecules in a volume and the diatomic nature of molecules on just a couple examples. He cited the results of many experiments. Still, the scientific community was not able to accept the validity of his hypothesis until many years after his death. Using his hypothesis, chemists were able to deduce the formulas of gaseous substances based on combining volumes. The use of this hypothesis was also instrumental in determining the molar mass of elements. Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 117 Consider the case of two colorless gases, nitric oxide and oxygen gas, reacting to form two volumes of a reddish-­‐brown gas. Sketch the product molecules in the two containers after the reaction arrow. Explain how you were able to deduce the formula of these molecules. Two volumes of hydrogen gas combine with one volume of oxygen gas to form two volumes of water vapor. Sketch the product molecules in the containers at the right. Dalton insisted until his death that the formula of water was OH. Why do we believe that the correct formula for water is H2O? Why must oxygen gas be diatomic? Two volumes of nitric oxide react with one volume of oxygen gas to form two volumes of a reddish-­‐brown gas. Deduce the formula of this gas and sketch particle representations of its molecules. Formula ______________ Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 118 Unit 4 Reading: Atoms from Democritus to Dalton
by Anthony Carpi, Ph.D.
Early humans easily distinguished between materials that
were used for making clothes, shaping into tools, or good to
eat, and they developed a language of words to describe these
things, such as “fur,” “stone,” or “rabbit.” However, these
people did not have our current understanding of the
substances that made up those objects. Empedocles, a Greek
philosopher and scientist who lived on the south coast of
Sicily between 492 BCE and 432 BCE, proposed one of the
first theories that attempted to describe the things around us.
Empedocles argued that all matter was composed of four elements: fire, air, water, and
earth. The ratio of these four elements affected the properties of the matter. Stone was
thought to contain a high amount of earth, while a rabbit was thought to have a higher
ratio of both water and fire, thus making it soft and giving it life. Empedocles’s theory was
quite popular, but it had a number of problems. For example, no matter how many times
you break a stone in half, the pieces never resemble any of the core elements of fire, air,
water, or earth. Despite these problems, Empedocles’s theory was an important
development in scientific thinking because it was among the first to suggest that some
substances that looked like pure materials, like stone, were actually made up of a
combination of different "elements."
A few decades after Empedocles, Democritus, another Greek who lived from 460 BCE to
370 b.c., developed a new theory of matter that attempted to overcome the problems of his
predecessor. Democritus’s ideas were based on reasoning rather than science, and drew on
the teachings of two Greek philosophers who came before him: Leucippus and Anaxagoras.
Democritus knew that if you took a stone and cut it in half, each half had the same
properties as the original stone. He reasoned that if you continued to cut the stone into
smaller and smaller pieces, at some point you would reach a piece so tiny that it could no
longer be divided. Democritus called these infinitesimally small pieces of matter atomos,
meaning "indivisible." He suggested that atomos were eternal and could not be destroyed.
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 119 Democritus theorized that atomos were specific to the material that they made up, meaning
that the atomos of stone were unique to stone and different from the atomos of other
materials, such as fur. This was a remarkable theory that attempted to explain the whole
physical world in terms of a small number of ideas.
Stone
Fur
Ultimately, though, Aristotle and Plato, two of the best-known philosophers of Ancient
Greece, rejected the theories of Democritus. Aristotle accepted the theory of Empedocles,
adding his own (incorrect) idea that the four core elements could be transformed into one
another. Because of Aristotle’s great influence, Democritus’s theory would have to wait
almost 2,000 years before being rediscovered.
In the seventeenth and eighteenth centuries CE, several key events helped revive the
theory that matter was made of small, indivisible particles. In 1643, Evangelista Torricelli,
an Italian mathematician and pupil of Galileo, showed that air had weight and was capable
of pushing down on a column of liquid mercury (thus inventing the barometer). This was a
startling finding. If air - this substance that we could not see, feel, or smell - had weight, it
must be made of something physical. But how could something have a physical presence,
yet not respond to human touch or sight? Daniel Bernoulli, a Swiss mathematician,
proposed an answer. He developed a theory that air and other gases consist of tiny particles
that are too small to be seen, and are loosely packed in an empty volume of space. The
particles could not be felt because unlike a solid stone wall that does not move, the tiny
particles move aside when a human hand or body moves through them. Bernoulli reasoned
that if these particles were not in constant motion they would settle to the ground like dust
particles; therefore he pictured air and other gases as loose collections of tiny billiard-balllike particles that are continuously moving around and bouncing
off one another.
Many scientists were busy studying the natural world at this
time. Shortly after Bernoulli proposed his theory, the
Englishman Joseph Priestley began to experiment with red
mercury calx in 1773. Mercury calx, a red solid stone, had been
known and coveted for thousands of years because when it is
heated, it appears to turn into mercury, a silver liquid metal.
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 120 Priestley had observed that it does not just turn into mercury; it actually breaks down into
two substances when it is heated, liquid mercury and a strange gas. Priestley carefully
collected this gas in glass jars and studied it. After many long days and nights in the
laboratory, Priestley said of the strange gas, “what surprised me more than I can well
express was that a candle burned in this air with a remarkably vigorous flame.” Not only
did flames burn strongly in this gas, but a mouse placed in a sealed container of this gas
lived for a longer period of time than a mouse placed in a sealed container of ordinary air.
Priestley’s discovery revealed that substances could combine together or break apart to
form new substances with different properties. For example, a colorless, odorless gas could
combine with mercury, a silver metal, to form mercury calx, a red mineral.
Priestley called the gas he discovered dephlogisticated air, but this name would not stick.
In 1778, Antoine Lavoisier, a French scientist, conducted many experiments with
dephlogisticated air and theorized that the gas made some substances acidic. He renamed
Priestley’s gas oxygen, from the Greek words that loosely translate as "acid maker". While
Lavoisier’s theory about oxygen and acids proved incorrect, his name stuck. Lavoisier knew
from other scientists before him that acids react with some metals to release another
strange and highly flammable gas called phlogiston. Lavoisier mixed the two gases,
phlogiston and the newly renamed oxygen, in a closed glass container and inserted a
match. He saw that phlogiston immediately burned in the presence of oxygen and
afterwards he observed droplets of water on the glass container. After careful testing,
Lavoisier realized that the water was formed by the reaction of phlogiston and oxygen, and
so he renamed phlogiston hydrogen, from the Greek words for "water maker". Lavoisier
also burned other substances such as phosphorus and sulfur in air, and showed that they
combined with air to make new materials. These new materials weighed more than the
original substances, and Lavoisier showed that the weight gained by the new materials was
lost from the air in which the substances were burned. From these observations, Lavoisier
established the Law of Conservation of Mass, which says that mass is not lost or gained
during a chemical reaction.
An eighteenth-century chemistry bench.
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 121 Priestley, Lavoisier, and others had laid the foundations of the field of chemistry. Their
experiments showed that some substances could combine with others to form new
materials; other substances could be broken apart to form simpler ones; and a few key
“elements” could not be broken down any further. But what could explain this complex set
of observations? John Dalton, an exceptional British teacher and scientist, put together the
pieces and developed the first modern atomic theory in 1803.
Dalton made it a regular habit to track and record the weather in his home town of
Manchester, England. Through his observations of morning fog and other weather
patterns, Dalton realized that water could exist as a gas that mixed with air and occupied
the same space as air. Solids could not occupy the same space as each other; for example,
ice could not mix with air. So what could allow water to sometimes behave as a solid and
sometimes as a gas? Dalton realized that all matter must be composed of tiny particles. In
the gas state, those particles floated freely around and could mix with other gases, as
Bernoulli had proposed. But Dalton extended this idea to apply to all matter – gases, solids
and liquids. Dalton first proposed part of his atomic theory in 1803 and later refined these
concepts in his classic 1808 paper A New System of Chemical Philosophy.
Dalton's Elements
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 122 Dalton's theory had four main concepts:
1. All matter is composed of indivisible particles called atoms. Bernoulli,
Dalton, and others pictured atoms as tiny billiard-ball-like particles in various
states of motion. While this concept is useful to help us understand atoms, it is not
correct, as we will see in later modules on atomic theory linked to at the bottom of
this module.
2. All atoms of a given element are identical; atoms of different elements
have different properties. Dalton’s theory suggested that every single atom of an
element such as oxygen is identical to every other oxygen atom; furthermore, atoms
of different elements, such as oxygen and mercury, are different from each other.
Dalton characterized elements according to their atomic weight; however, when
isotopes of elements were discovered in the late 1800s this concept changed.
3. Chemical reactions involve the combination of atoms, not the destruction
of atoms. Atoms are indestructible and unchangeable, so compounds, such as
water and mercury calyx, are formed when one atom chemically combines with
other atoms. This was an extremely advanced concept for its time; while Dalton’s
theory implied that atoms bonded together, it would be more than 100 years before
scientists began to explain the concept of chemical bonding.
4. When elements react to form compounds, they react in defined, wholenumber ratios. The experiments that Dalton and others performed showed that
reactions are not random events; they proceed according to precise and well-defined
formulas. This important concept in chemistry is discussed in more detail below.
Some of the details of Dalton’s atomic theory require more explanation.
Elements: As early as 1660, Robert Boyle recognized that the Greek definition of element
(earth, fire, air, and water) was not correct. Boyle proposed a new definition of an element
as a fundamental substance, and we now define elements as fundamental substances that
cannot be broken down further by chemical means. Elements are the building blocks of the
universe. They are pure substances that form the basis of all of the materials around us.
Some elements can be seen in pure form, such as mercury in a thermometer; some we see
mainly in chemical combination with others, such as oxygen and hydrogen in water. We
now know of approximately 116 different elements. Each of the elements is given a name
and a one- or two-letter abbreviation. Often this abbreviation is simply the first letter of the
element; for example, hydrogen is abbreviated as H, and oxygen as O. Sometimes an
element is given a two-letter abbreviation; for example, helium is He. When writing the
abbreviation for an element, the first letter is always capitalized and the second letter (if
there is one) is always lowercase.
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 123 Atoms: A single unit of an element is called an atom. The atom is the most basic unit of
matter, which makes up everything in the world around us. Each atom retains all of the
chemical and physical properties of its parent element. At the end of the nineteenth
century, scientists would show that atoms were actually made up of smaller, "subatomic"
pieces, which smashed the billiard-ball concept of the atom (see our Atomic Theory I: The
Early Days module).
Compounds: Most of the materials we come into contact with are
compounds, substances formed by the chemical combination of two
or more atoms of the elements. A single “particle” of a compound is
called a molecule. Dalton incorrectly imagined that atoms
“hooked” together to form molecules. However, Dalton correctly
realized that compounds have precise formulas. Water, for
example, is always made up of two parts hydrogen and one part oxygen. The chemical
formula of a compound is written by listing the symbols of the elements together, without
any spaces between them. If a molecule contains more than one atom of an element, a
number is subscripted after the symbol to show the number of atoms of that element in the
molecule. Thus the formula for water is H2O, never HO or H2O2.
The idea that compounds have defined chemical formulas was first proposed in the late
1700s by the French chemist Joseph Proust. Proust performed a number of experiments
and observed that no matter how he caused different elements to react with oxygen, they
always reacted in defined proportions. For example, two parts of hydrogen always reacts
with one part oxygen when forming water; one part mercury always reacts with one part
oxygen when forming mercury calx. Dalton used Proust’s Law of Definite Proportions in
developing his atomic theory.
The law also applies to multiples of the fundamental proportion, for example:
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 124 In both of these examples, the ratio of hydrogen to oxygen to water is 2 to 1 to 1. When
reactants are present in excess of the fundamental proportions, some reactants will remain
unchanged after the chemical reaction has occurred.
The story of the development of modern atomic theory is one in which scientists built upon
the work of others to produce a more accurate explanation of the world around them. This
process is common in science, and even incorrect theories can contribute to important
scientific discoveries. Dalton, Priestley, and others laid the foundation of atomic theory,
and many of their hypotheses are still useful. However, in the decades after their work,
other scientists would show that atoms are not solid billiard balls, but complex systems of
particles. Thus they would smash apart a bit of Dalton’s atomic theory in an effort to build
a more complete view of the world around us.
Anthony Carpi, Ph.D. "Matter: Atoms from Democritus to Dalton," Visionlearning Vol. CHE-1 (1), 2003.
http://www.visionlearning.com/library/module_viewer.php?mid=49
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 125 Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 126 Name:______________________________________
Veritas:______________________________________
Unit 4, Worksheet 4—
Atoms from Democritus to Dalton
1. Explain the importance of Empedocles’s (492 BC- 432 BC) theory of matter.
2. Explain the problems with Empedocles’s theory of matter.
3. A few decades after Empedocles, Democritus developed a new theory of
matter that attempted to overcome the problems with Empedocles’s theory.
Describe Democritus’s theory.
4. Why did it take almost 2,000 years for Democritus’s theory to be
rediscovered?
5. How did Evangelista Torricelli (in 1643) find that air is made of something
physical?
6. Based on Torricelli’s findings, Daniel Bernoulli proposed how something
could have a physical presence, yet not respond to human touch or sight.
Describe his proposal.
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 127 7. Explain how Joseph Priestley’s experiments with mercury calx aided in our
understanding of matter.
8. Describe Antoine Lavoisier’s contributions to laying the foundations of
chemistry.
9. Describe Dalton’s Theory:
a.
b.
c.
d.
10. Describe elements.
11. Describe atoms.
12. Describe compounds and molecules.
13. Describe the Law of Definite Proportions.
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 128 Name:______________________________________
Veritas:______________________________________
Unit 4, Worksheet 5—Dalton’s Playhouse
In the late 18th century, Joseph Priestly, Antoine Lavoisier and others performed some critical
experiments that helped Dalton develop his theories on the atomic model of matter. The simulation at
the website: http://web.visionlearning.com/dalton_playhouse/ad_loader.html will allow you to
replicate some of the key experiments these scientists performed. Answer the questions on the website
and keep track of your responses on this notes sheet.
Part 1 – Priestley
Calx
Mass of mercury left in flask
Mass of gas produced
Volume of gas produced
100g
200g
216.59g
1. What happened to the mass of the material in the flask as it was heated?
2. What did you note about the masses of the gas produced and the mercury metal left in the
flask?
3. State the relationship between the volume of gas produced and the mass of the calx that
was heated.
Part 2 – Lavoisier
Burn 1/3
Burn 2/3
Burn all
Burn 1/3
Burn 2/3
Burn all
Initial mass of oxygen
Initial mass of phlogiston
Initial volume of oxygen
Initial volume of phlogiston
Final mass of oxygen
Final mass of phlogiston
Final volume of oxygen
Final volume of phlogiston
Mass oxygen used
Mass phlogiston used
Mass of product
Volume oxygen used
Volume phlogiston used
Volume of product
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 129 4. With relation to the volumes of the gases, in what specific proportion did phlogiston react
with oxygen?
5. How did the mass of the gas in all three vessels before burning compare to the total mass
after burning?
Part 3 – Diamond and Charcoal
0.20g diamond
initial
Mass O2
Volume O2
Mass product
Volume product
Mass O2
Volume O2
Mass product
Volume product
Mass O2
Volume O2
Mass product
Volume product
Mass O2
Volume O2
Mass product
Volume product
final
0.40g diamond
initial
final
0.20g charcoal
initial
final
0.40g charcoal
initial
final
6. How did the mass of gas formed compare if you used the same amount of diamond and
charcoal?
Concepts
7. Which of the core concepts below most logically follows from the experiments you
conducted in Track 1- Priestley?
a. Red calyx turns into mercury when it is heated.
b. Some substances are composed of discrete amounts of two or more other
substances.
c. All substances can be broken down into simpler materials by heating them.
8. Which of the core concepts below most logically follows from the experiments you
conducted in Track 2- Lavoisier?
a. The total mass of the products in a chemical reaction is greater than the mass of
the reactants.
b. The total mass of the products in a chemical reaction is less than the mass of the
reactants.
c. The total mass of the products in a chemical reaction is exactly equal to the mass
of the reactants.
9. Which of the core concepts below most logically follows from the experiments you
conducted in Track 3- Diamond?
a. Elements combine in specific, defined ratios in chemical reactions.
b. Carbon reacts differently depending whether it is in the diamond or charcoal form.
c. Carbon can form carbon dioxide when neither air nor oxygen is present.
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 130 Name:______________________________________
Veritas:______________________________________
Unit 4, Worksheet 6—
Multiple Proportions
Use the following information about the masses of elements in each pair of
compounds to help you suggest formulas that account for these ratios.
1. Compounds of carbon and oxygen Compound A: 57.1 g O / 42.9 g C Compound B: 72.7 g O / 27.3 g C a. Determine the value of the ratio mass O
in each compound. A ____ B _____ mass C
b. In words, describe what the ratios above tell you. A: €
B: c. How does the mass ratio for compound B compare to that in compound A? d. Express these ratios as improper fractions. e. For each hypothesis, sketch particle diagrams for the compounds of A and B that account for these mass ratios. Write the formula for the compound in each diagram. Hypothesis 1 Atoms of C and O have the same mass A B Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School Hypothesis 2 Atoms of O are heavier than C atoms by the ratio in compound A. A B 131 2. Compounds of copper and oxygen Compound A: 79.9 g Cu / 20.1 g O Compound B: 88.8 g Cu / 11.2 g O a. Determine the value of the ratio mass Cu
in each compound. A ____ B_____ mass O
b. In words, describe what the ratios above tell you. A: B: €
c. How does the mass ratio for compound B compare to that in compound A? d. Express these ratios as improper fractions. e. For each hypothesis, sketch particle diagrams for the compounds of A and B that account for these mass ratios. Write the formula for the compound in each diagram. Hypothesis 1 Atoms of Cu and O have the same mass A B Hypothesis 2 Cu atoms are heavier than O atoms by the ratio in compound A. A B Which hypothesis seems more reasonable to you? Justify your answer. Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 132 Use the hypothesis you have chosen to suggest formulas for the following pairs of compounds. 3. Compounds of copper and chlorine Compound A: 35.9 g of Cl / 64.1 g of Cu Compound B: 52.8 g of Cl / 47.2 g Cu a. Determine the value of the ratio 4. mass Cl
in each compound. A ____ B ____ mass Cu
b. In words, describe what the ratios above tell you. A: B: €
b. How does the mass ratio for compound B compare to that in compound A? c. What are the simplest formulas for compounds A and B? Explain your reasoning. Compounds of iron and chlorine Compound A: 56.0 g of Cl / 44.0 g of Fe Compound B: 65.6 g of Cl / 34.4 g of Fe a. Determine the value of the ratio mass Cl
in each compound. A ____ B ____ mass Fe
b. In words, describe what the ratios above tell you. A: €
B: b. The ratios you determined in step (a) give the mass of Cl that combines with 1 g of Fe in each compound. To determine how the mass of Cl in compound B compares to the mass of Cl in compound A for the same amount of Fe, divide these ratios and express the answer as an improper fraction. What does this fraction tell you about the number of Cl atoms in each of the two compounds? c. What would be the formulas of the two compounds, assuming that each compound contains one atom of Fe? Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 133 Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 134 Name:______________________________________
Veritas:______________________________________
Unit 4, Worksheet 7—
Percent Composition
Show all work/reasoning and use complete sentences in explanations.
1. Table sugar is a compound known as sucrose. Sucrose is composed of the
elements carbon, hydrogen, and oxygen. Analysis of a 20.0 g of sucrose from a
bag of sugar finds that the sugar is composed of 8.44 g of carbon, 1.30 g of
hydrogen, and 10.26 g of oxygen.
a. Express, as fractions, the ratio of the mass of each element to the total
mass of the sample.
b. Using these ratios, calculate the percent composition by mass of each
element in the compound.
2. A similar chemical analysis is performed on a 500.0 g sample of the sugar
isolated from a sample of pure sugar cane. Analysis shows this sample
contains 211.0 g of carbon, 32.5 g of hydrogen, and 256.5 g of oxygen.
a. Determine the percent composition by mass of each element in the sugar
cane sample.
b. Could the sugar in this sample be sucrose? Justify your conclusion.
3. A similar chemical analysis is performed on a 200.0g sample of the
sugar found in corn syrup. This sample contains 80.0g of carbon, 13.3 g of
hydrogen and 106.7 g of oxygen.
a. Determine the percent composition by mass of each element in the sugar
cane sample.
b. Could the sugar in corn syrup be sucrose? Justify your conclusion.
4. A 1.0 g sample of hydrogen reacts completely with 19.0 g of fluorine to
form a compound of hydrogen and fluorine.
a. What is the percent by mass of each element in the compound?
b. What mass of hydrogen would be present in a 50 g sample of this
compound?
c. Justify your answer to b.
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 135 5. Explain how the previous examples help to illustrate the Law of
Definite Proportions.
6. Two compounds of hydrogen and oxygen are tested. Compound I
contains 15.0 g of hydrogen and 120.0 g of oxygen. Compound II contains 2.0 g of
hydrogen and 32.0 g of oxygen.
a. Determine the ratio of the mass of oxygen to the mass of hydrogen in each
of the compounds.
b. Why are the compounds not the same?
c. What is significant about these mass ratios?
d. If compound I is water, what could be the formula of compound II?
7. Nitrogen and oxygen combine to form a variety of compounds. The
following data were collected for three different compounds of nitrogen and
oxygen:
Analysis Data of Nitrogen & Oxygen Compounds
Compound
Mass of Nitrogen that combines
with 1.00 g of Oxygen
A
1.750 g
B
0.8750 g
C
0.4375 g
a. Additional evidence shows that the formula of compound B is NO. Sketch
particle diagrams of molecules of all three compounds.
b. Justify your representations above.
8. Explain how the examples in questions 6 and 7 help to illustrate the
Law of Multiple Proportions.
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 136 Name:______________________________________
Veritas:______________________________________
Unit 4—Extra Practice Problems
Complete the following chart depicting the types of matter. Word bank: homogeneous,
gas, compound, mixture, liquid, pure substance, matter, homogeneous, element, solid.
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 137 For each box, first describe the substance as a pure substance or a mixture. Then
describe whether it contains a(n) element(s), compound(s), or both. (Example: Mixture
containing an element and a compound)
1.
2.
3.
4.
5.
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 138 6. Identify the separation techniques pictured below.
Which technique would be useful to separate a mixture of sulfur and water?
Of salt and water?
7. Describe the process of fractional distillation and include a temperature-time
graph in your explanation.
8. What are the seven diatomic elements? Show how you would draw these
elements in a particle diagram.
9. How would you separate a mixture of sand and iron fillings?
10. What is Avogadro’s hypothesis?
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 139 11. Making sure you are consistent with Avogadro’s hypothesis draw particle
diagrams showing 2 volumes of hydrogen gas reacting with 1 volume of oxygen
gas.
Explain why molecules of oxygen must have an even number of atoms (diatomic).
12. Describe the laws of definite and multiple proportions.
13. Nitrogen and oxygen form several compounds. Two of these have the
following mass composition.
Compound A: 182 g of N and 104 g of O
Compound B:
45.6g of N and 52.1 g of O
a. Determine the value of the ratio
mass N
in each compound. A ____ B _____
mass O
b. In words, describe what the ratios above tell you.
A:
B:
€
c. How does the mass ratio for compound A compare to that in compound
B?
d. Sketch particle diagrams for the compounds of A and B that account
for these mass ratios. Write the formula for the compound in each diagram.
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 140 14. Sulfur and oxygen form several compounds. Two of these have the
following mass composition.
Compound A: 19.6 g of S and 22.4 g of O
Compound B: 63.3 g of S and 144.6 g of O
e. Determine the value of the ratio
f.
mass S
in each compound. A ____ B _____
mass O
In words, describe what the ratios above tell you.
A:
B:
g. How does the mass ratio for compound A compare to that in compound
B?
h. Sketch particle diagrams for the compounds of A and B that account
for these mass ratios. Write the formula for the compound in each diagram.
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 141 Classify each of the materials below. In the center column, state whether the material
is a pure substance or a mixture. If the material is a pure substance, further
classify it as either an element or compound in the right column. Similarly, if the
material is a mixture, further classify it as homogeneous or heterogeneous in the
right column.
Material:
Pure or Mixture:
Element, Compound,
Heterogeneous, Homogeneous
concrete
sugar + pure water
(C12H22O11 + H2O)
iron filings (Fe)
limestone (CaCO3)
orange juice (w/pulp)
Pacific Ocean
air inside a balloon
aluminum (Al)
magnesium (Mg)
acetylene (C2H2)
tap water in a glass
soil
pure water (H2O)
chromium (Cr)
Chex mix
salt + pure water
(NaCl + H2O)
benzene (C6H6)
muddy water
brass
(Cu mixed with Zn)
baking soda (NaHCO3)
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 142 Classify each of the pictures below by placing the correct label in the blanks below:
A= Element
D= Mixture of compounds
B= Compound
E= Mixture of elements and compounds
C= Mixture of elements
Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 143 Modeling Chemistry TN Modeling Curriculum Committee Pope John Paul II High School 144