ACT Science : How to find conflicting viewpoints in chemistry
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Example Question #178 : Chemistry
In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."
Below, two scientists discuss how rust forms and the composition of rust.
Scientist 1:
Both water and oxygen are needed for rust to form. Water is an electrolyte, meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.
Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.
Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.
Scientist 2:
Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.
Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.
Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.
In an experiment, oxygen is removed from water by boiling the water. This water is then poured into a flask, and a piece of iron is immersed in the water. Excess air is pumped out from the flask and replaced with helium (He). Then the flask is sealed. After an extended period of time, a reddish-orange substance is observed on the surface of the iron.
Given that Scientist 2 is correct, which of the following most likely describes the identity of the reddish-orange substance?
The substance is not rust, because rust requires carbonic acid to form.
The substance is not rust, because rust requires oxygen to form.
The substance is rust, because rust forms in the presence of oxygen.
The substance is rust, because rust forms in the presence of carbonic acid.
The substance is not rust, because rust requires oxygen to form.
The explanation of Scientist 2 requires that oxygen be dissolved in water in order for rust to form. According to Scientist 2, free iron (Fe2+) ions react with dissolved atmospheric oxygen to form iron oxide. However, in this question, dissolved oxygen is removed from the water by boiling, and no additional oxygen is allowed to diffuse into the water, because the air is replaced with helium. Because no oxygen can get into the water, it would be impossible for rust to form. So, the reddish-orange substance must be another compound instead of rust.
Example Question #179 : Chemistry
In studying the effects of adding heat to different substances on each substance's temperature, a researcher conducted the following experiment. The researcher added 1,000 Joules of energy by a controlled heat lamp to four different substances. The temperature change in each substance that was caused by the heat was then measured and recorded. The results of this experiment are shown below.
The researcher is aware of a concept called specific heat and knows that lead has a lower specific heat than wood, which has a lower specific heat than cardboard, which has a lower specific heat than styrofoam. Therefore, the researcher has ordered the objects in the table from lowest specific heat (lead) to highest (styrofoam).
According to the data in the table, what is the apparent relationship between specific heat and the amount that an object's temperature changes when a given amount of heat is added?
There is no apparent relationship.
A positive correlation.
The data for different amounts of heat added is needed to discern a relationship.
The data for specific heat is needed to discern a relationship.
A negative correlation
A negative correlation
Since the objects are ordered from lowest specific heat to highest and we see that the degree to which an object's temperature changes decreases as we go down the chart, we see a clear negative correlation. No more information is needed to discern this.
Example Question #171 : Chemistry
When describing their behavior, gases are typically treated as "ideal gases" in what is known as the ideal gas law. Two science students describe the ideal gas law in their own terms:
Student 1: The ideal gas law is based on the assumptions that a gas consists of a large number of molecules and that gas molecules take up negligible space in a gas due to their minuscule size in comparison to the space between each gas molecule. Also important is the assumption that all of the forces acting on gas molecules are from collisions with other gas molecules or a container and not from anything else. According to the ideal gas law, all gases behave the same so long as those assumptions hold true. Therefore, if you measure the volume of helium gas at a certain temperature and pressure, an equivalent amount of radon gas (a much heavier gas) at the same conditions will have the same volume.
Student 2: The ideal gas law's primary assumption is that a gas consists of a very large number of particles. For example, even within a single bacteria there can be billions of gas molecules despite the bacteria's very small size. Therefore, in a room full of gas, there are so many particles that their random behavior is, on average, uniform. There are exceptions to the ideal gas law and those are gases with very high inter-molecular forces of attraction (IMFAs). A gas with high IMFA will behave very differently than a gas with a low IMFA. As one could imagine, because a gas with a high IMFA will have molecules that tend to attract each other, that gas will display a lower volume than that which would be predicted by the ideal gas law.
Based on the passage, which of the following statements best describes where Student 1 and Student 2 disagree?
Student 2 would not consider molecule size to be important in the ideal gas law.
Student 1 would not consider molecule size to be important in the ideal gas law.
Student 1 would not consider IMFAs to be important in the ideal gas law.
The students do not disagree.
Student 2 would not consider IMFAs to be important in the ideal gas law.
Student 2 would not consider molecule size to be important in the ideal gas law.
This is a very tricky question because it is very tempting to answer that Student 1 did not recognize the possible influence of IMFAs on gas behavior since Student 1 did not mention IMFAs directly. This is why it is so important to read a passage very carefully. Although Student 1 does not specifically mention IMFAs, one can conclude from the passage that an IMFA is a force that acts on gas molecules that Student 1 points out would violate an important assumption of the ideal gas law. Therefore, student 1, while not using the term "IMFA," would likely agree that IMFAs would have an effect on ideal gas behavior. Instead, the answer is that Student 2 would not consider molecule size to be important. This we can assume because Student 2 did not mention molecule size whatsoever.
Example Question #181 : Chemistry
When describing their behavior, gases are typically treated as "ideal gases" in what is known as the ideal gas law. Two science students describe the ideal gas law in their own terms:
Student 1: The ideal gas law is based on the assumptions that a gas consists of a large number of molecules and that gas molecules take up negligible space in a gas due to their minuscule size in comparison to the space between each gas molecule. Also important is the assumption that all of the forces acting on gas molecules are from collisions with other gas molecules or a container and not from anything else. According to the ideal gas law, all gases behave the same so long as those assumptions hold true. Therefore, if you measure the volume of helium gas at a certain temperature and pressure, an equivalent amount of radon gas (a much heavier gas) at the same conditions will have the same volume.
Student 2: The ideal gas law's primary assumption is that a gas consists of a very large number of particles. For example, even within a single bacteria there can be billions of gas molecules despite the bacteria's very small size. Therefore, in a room full of gas, there are so many particles that their random behavior is, on average, uniform. There are exceptions to the ideal gas law and those are gases with very high inter-molecular forces of attraction (IMFAs). A gas with high IMFA will behave very differently than a gas with a low IMFA. As one could imagine, because a gas with a high IMFA will have molecules that tend to attract each other, that gas will display a lower volume than that which would be predicted by the ideal gas law.
Assuming that both students' statements are correct in describing the ideal gas law, how would we then describe the effects of molecule size and IMFAs on a gas's volume?
Higher IMFAs would lead to a volume greater than predicted by the ideal gas law and high molecule size would lead to lower volume than predicted by the ideal gas law.
Higher IMFAs would lead to a volume lower than predicted by the ideal gas law and high molecule size would lead to lower volume than predicted by the ideal gas law.
More information is necessary to make such a conclusion.
Higher IMFAs would lead to a volume lower than predicted by the ideal gas law and high molecule size would lead to greater volume than predicted by the ideal gas law.
Higher IMFAs would lead to a volume greater than predicted by the ideal gas law and high molecule size would lead to greater volume than predicted by the ideal gas law.
Higher IMFAs would lead to a volume lower than predicted by the ideal gas law and high molecule size would lead to greater volume than predicted by the ideal gas law.
The correct answer is that a greater IMFA would lead to a smaller volume and a greater molecule size would lead to larger volume. Student 2's statement about IMFAs shows us that greater attraction between molecules would lead to a smaller volume than predicted by the ideal gas law. Student 1's claim is a little bit more subtle. Student 1 says that one of the assumptions about the ideal gas law is that we are treating molecule size as negligible compared to the space between each molecule. If we are ignoring the volume these molecules take up, then a gas with very large molecules may leave this assumption to be invalid. Therefore, if we consider the volume that gas molecules occupy, we can assume the volume would be greater than what would be predicted by ignoring the volume they occupy.
Example Question #182 : Chemistry
When describing their behavior, gases are typically treated as "ideal gases" in what is known as the ideal gas law. Two science students describe the ideal gas law in their own terms:
Student 1: The ideal gas law is based on the assumptions that a gas consists of a large number of molecules and that gas molecules take up negligible space in a gas due to their minuscule size in comparison to the space between each gas molecule. Also important is the assumption that all of the forces acting on gas molecules are from collisions with other gas molecules or a container and not from anything else. According to the ideal gas law, all gases behave the same so long as those assumptions hold true. Therefore, if you measure the volume of helium gas at a certain temperature and pressure, an equivalent amount of radon gas (a much heavier gas) at the same conditions will have the same volume.
Student 2: The ideal gas law's primary assumption is that a gas consists of a very large number of particles. For example, even within a single bacteria there can be billions of gas molecules despite the bacteria's very small size. Therefore, in a room full of gas, there are so many particles that their random behavior is, on average, uniform. There are exceptions to the ideal gas law and those are gases with very high inter-molecular forces of attraction (IMFAs). A gas with high IMFA will behave very differently than a gas with a low IMFA. As one could imagine, because a gas with a high IMFA will have molecules that tend to attract each other, that gas will display a lower volume than that which would be predicted by the ideal gas law.
An experiment was carried out that measured the volumes of two very small quantities of gases, hydrogen and tetrachloromethane. Both gases have a dipole moment of zero, meaning they do not exhibit intermolecular forces of attraction. Hydrogen is the lightest known gas, while tetrachloromethane is much heavier and therefore has much larger molecules.
The experiment yielded the following result: the same number of hydrogen molecules occupied a slightly different volume than an equivalent quantity of tetrachloromethane. This remained true only for small quantities of both gases.
What does this experimental data mean with regard to the opinions of the two students above?
This information supports the statements of Student 2.
This information supports the statements of Student 1.
This information refutes the statements of Student 1.
This information supports the statements of both Student 1 and Student 2.
This information refutes he statements of Student 2.
This information supports the statements of Student 1.
The answer is that this information supports the opinion of Student 1. This can be tricky because supporting Student 1 does not necessarily mean refuting Student 2's statements. This is an important distinction in the scientific process. Student 2 simply failed to mention molecule size in the given description of the ideal gas law's assumptions. This new information does not then refute the statements that Student 2 did make, since Student 2 did not mention molecular size; however, this information does appear to suggest that large differences in molecular size does affect measured volume when working with small quantities of gas. Indeed, this is consistent with Student 1's description, which emphasized that treating molecule size as negligible is a general assumption. Therefore, it may not hold true at small volumes where space between molecules may not be enough to make the assumption.
It should be noted that this in fact is how gases work. They tend to deviate from ideal behavior only at high pressures, low temperatures, and small volumes.
Example Question #181 : Chemistry
Enzymes (large molecules) serve to catalyze, or speed up, chemical reactions in the human body. This process of catalysis begins with the binding of a substrate (the reactant) to the active site of an enzyme. This active site is simply the portion of the enzyme that interacts with the substrate. Following the binding event, products separate from the enzyme active site, at which point the enzyme is prepared to undergo another reaction cycle. Two scientists offer conflicting views on the nature of the enzyme-substrate interaction.
Scientist 1
The enzyme-substrate interaction can be modeled with a Lock and Key paradigm. In this model, the enzyme represents a lock and the substrate represents a key. Only the substrate of proper size and shape will fit into a particular enzyme's active site and catalyze the reaction. The enzyme-substrate complex, the intermediate of this reaction, is stabilized mostly by strong ionic and hydrogen bonds. Following the formation of this intermediate, the enzyme changes the substrate in some way, leading to formation of a product, which subsequently dissociates from the enzyme.
Scientist 2
The shapes of substrate and enzyme are not exactly complementary. When it binds to the enzyme, the substrate induces the active site to alter its shape in order to enhance the fit. Thus, at first the interaction between substrate and enzyme is weak, but subsequent changes in the active site lead to stronger binding. Only the correct substrate will be able to modify the active site in the proper manner. Experimental data seems consistent with this Induced Fit model and inconsistent with the Lock and Key model.
Which model of the enzyme-substrate interaction would require a highly flexible enzyme?
Induced Fit, because, according to this model, the active site is static.
Lock and Key, because, according to this model, the active site must change shape.
Lock and Key, because, according to this model, the active site is static.
Induced Fit, because, according to this model, the shape of the active site must change shape.
Induced Fit, because, according to this model, the shape of the active site must change shape.
In the Induced Fit model, the shape of the enzyme's active site changes to accommodate the substrate. Thus, the enzyme must be highly flexible.
Example Question #861 : Act Science
Enzymes (large molecules) serve to catalyze, or speed up, chemical reactions in the human body. This process of catalysis begins with the binding of a substrate (the reactant) to the active site of an enzyme. This active site is simply the portion of the enzyme that interacts with the substrate. Following the binding event, products separate from the enzyme active site, at which point the enzyme is prepared to undergo another reaction cycle. Two scientists offer conflicting views on the nature of the enzyme-substrate interaction.
Scientist 1
The enzyme-substrate interaction can be modeled with a Lock and Key paradigm. In this model, the enzyme represents a lock and the substrate represents a key. Only the substrate of proper size and shape will fit into a particular enzyme's active site and catalyze the reaction. The enzyme-substrate complex, the intermediate of this reaction, is stabilized mostly by strong ionic and hydrogen bonds. Following the formation of this intermediate, the enzyme changes the substrate in some way, leading to formation of a product, which subsequently dissociates from the enzyme.
Scientist 2
The shapes of substrate and enzyme are not exactly complementary. When it binds to the enzyme, the substrate induces the active site to alter its shape in order to enhance the fit. Thus, at first the interaction between substrate and enzyme is weak, but subsequent changes in the active site lead to stronger binding. Only the correct substrate will be able to modify the active site in the proper manner. Experimental data seems consistent with this Induced Fit model and inconsistent with the Lock and Key model.
Assuming Scientist 2 is correct, one would be least likely to find which of the following in the active site when an enzyme initially binds its substrate?
A loose fit
Weak London dispersion forces
Weak dipole-dipole interactions
Strong ionic bonds
Strong ionic bonds
Scientist 2 claims that, when the enzyme initially binds its substrate, the interaction is weak. Therefore, we would not expect to find strong ionic bonds at this point. These strong ionic bonds would occur in a Lock and Key model.
Example Question #21 : How To Find Conflicting Viewpoints In Chemistry
Acids and bases are chemical substances that react with each other and certain other elements to produce compounds like salts. Chemists have discussed the unique reaction between acids and bases significantly, here are three major theories that attempt to explain how acids and bases react.
Theory 1: The Arrhenius acid/base theory focuses on hydrogen, and how acids and bases neutralize each other to form salt and water. Acids dissociate in a solution into hydrogen ions 
Theory 2: The Bronsted-Lowry theory concerns the donation of hydrogen ions from acids to bases and the formation of conjugate pairs. This theory defines acids as the substance that donates a proton, and bases as the substance that accepts the proton. Because reactions can be reversible, acids that have their hydrogen ion removed become that acid’s conjugate base, while bases that receive that hydrogen ion become the original base’s conjugate acid. This is true because if the reaction is reversed, the former-acid with its missing proton will be receiving the hydrogen ion (making it the base) and the former-base with the additional proton will be donating it (making it the acid). Reactions then produce new bases and acids, and do not neutralize to produce salts and water. This acid-base theory does not require a solvent.
Theory 3: The Lewis theory discards the concern with hydrogen ions and focuses on electron-pair donation. According to this theory, acids are substances that can receive an electron pair whereas bases are substances that can donate an electron pair. This broadens the consideration of what is a base or an acid even further, eliminating the need to define substances based on their use of a hydrogen ion. Compounds that have vacancies in their electron octets can be considered Lewis acids, and compounds with extra electrons in their octets can be considered Lewis bases.
Which of the following would be correct under all three theories?
Acid-base reactions produce water and salts
Acid-base reactions take at least several hours
None of the other answers are correct
Acid-base reactions can produce water
Acid-base reactions can produce water
All three theories support the claim that acid-base reactions can produce water, either through the movement of hydrogen ions or the bonding of electron pairs. Only theory 1 states that acid-base reactions will produce water and salts. There is no discussion of the length of acid-base reactions in any of the theories.
Example Question #181 : Chemistry
Acids and bases are chemical substances that react with each other and certain other elements to produce compounds like salts. Chemists have discussed the unique reaction between acids and bases significantly, here are three major theories that attempt to explain how acids and bases react.
Theory 1: The Arrhenius acid/base theory focuses on hydrogen, and how acids and bases neutralize each other to form salt and water. Acids dissociate in a solution into hydrogen ions 
Theory 2: The Bronsted-Lowry theory concerns the donation of hydrogen ions from acids to bases and the formation of conjugate pairs. This theory defines acids as the substance that donates a proton, and bases as the substance that accepts the proton. Because reactions can be reversible, acids that have their hydrogen ion removed become that acid’s conjugate base, while bases that receive that hydrogen ion become the original base’s conjugate acid. This is true because if the reaction is reversed, the former-acid with its missing proton will be receiving the hydrogen ion (making it the base) and the former-base with the additional proton will be donating it (making it the acid). Reactions then produce new bases and acids, and do not neutralize to produce salts and water. This acid-base theory does not require a solvent.
Theory 3: The Lewis theory discards the concern with hydrogen ions and focuses on electron-pair donation. According to this theory, acids are substances that can receive an electron pair whereas bases are substances that can donate an electron pair. This broadens the consideration of what is a base or an acid even further, eliminating the need to define substances based on their use of a hydrogen ion. Compounds that have vacancies in their electron octets can be considered Lewis acids, and compounds with extra electrons in their octets can be considered Lewis bases.
Which theory would most likely consider the greatest number of substances as acids or bases?
There is no difference in the number of acids or bases between these theories
Theory 3
Theory 1
Theory 2
Theory 3
Theory 3 considers the greatest number of substances acids or bases because it has the broadest definition for what constitutes an acid or a base. Any compound that has missing spots in its electron octet can be considered an acid, and any compound with extra electrons a base. The other theories require the presence of hydrogen ions for such a designation.
Example Question #862 : Act Science
Acids and bases are chemical substances that react with each other and certain other elements to produce compounds like salts. Chemists have discussed the unique reaction between acids and bases significantly, here are three major theories that attempt to explain how acids and bases react.
Theory 1: The Arrhenius acid/base theory focuses on hydrogen, and how acids and bases neutralize each other to form salt and water. Acids dissociate in a solution into hydrogen ions 
Theory 2: The Bronsted-Lowry theory concerns the donation of hydrogen ions from acids to bases and the formation of conjugate pairs. This theory defines acids as the substance that donates a proton, and bases as the substance that accepts the proton. Because reactions can be reversible, acids that have their hydrogen ion removed become that acid’s conjugate base, while bases that receive that hydrogen ion become the original base’s conjugate acid. This is true because if the reaction is reversed, the former-acid with its missing proton will be receiving the hydrogen ion (making it the base) and the former-base with the additional proton will be donating it (making it the acid). Reactions then produce new bases and acids, and do not neutralize to produce salts and water. This acid-base theory does not require a solvent.
Theory 3: The Lewis theory discards the concern with hydrogen ions and focuses on electron-pair donation. According to this theory, acids are substances that can receive an electron pair whereas bases are substances that can donate an electron pair. This broadens the consideration of what is a base or an acid even further, eliminating the need to define substances based on their use of a hydrogen ion. Compounds that have vacancies in their electron octets can be considered Lewis acids, and compounds with extra electrons in their octets can be considered Lewis bases.
Suppose a new discovery finds that acid-base reactions are not actually reversible. Which concept would this discovery most completely disprove?
Conjugate pairs
Electron donation
The production of salts from an acid-base reaction
Pure water being neither acidic nor basic
Conjugate pairs
As stated in the passage, the idea of conjugate pairs in theory 2 is based on the reversibility of acid-base reactions. The other answers do not rely on this, and would not be impacted to the same degree as conjugate pairs.
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