Student Solutions Manual: for Chemistry: An Atoms-Focused Approach (Third Edition)
Genres: Chemistry
Book Preface
Collect and Organize
Figure P1.1(a) shows “molecules,” each consisting of one red sphere and one blue sphere, and Figure P1.1(b) shows separate blue spheres and red spheres. For each image we are to identify the class of matter. We need to determine whether the substance(s) depicted is/are solid, liquid, or gas and whether the images show an element, a compound, or a mixture that is homogeneous or heterogeneous.
Analyze
An element is composed of all the same type of atom, and a compound is composed of two or more types of atoms. Solids have a definite volume and a highly ordered arrangement where the particles are close together. Liquids also have a definite volume but have a disordered arrangement of particles that are close together. Gases have disordered particles that fill the volume of the container and are far apart from each other. Homogeneous mixtures have a uniform distribution and composition, and heterogeneous mixtures contain regions of different composition.
Solve
- Because each particle in Figure P1.1(a) consists of one red sphere and one blue sphere, all the particles are the same—that is a compound. The particles fill the container and are disordered, so those particles are in the gas phase.
- Because it shows a mixture of red and blue spheres, Figure P1.1(b) depicts a mixture of blue elemental atoms and red elemental atoms. The blue spheres fill the container and are disordered, so those particles are in the gas phase. The red spheres have a definite volume and are ordered, so those particles are in the solid phase. This is a heterogeneous mixture.
Think About It
Remember that both elements and compounds may be either pure or present in a mixture.
1.3.
Collect and Organize
In this question we are to consider whether the reactants, as depicted, undergo a chemical reaction and/or a phase change.
Analyze
Chemical reactions involve the breaking and making of bonds in which atoms are combined differently in the products than in the reactants. When we consider a possible phase change, remember the following: Solids have a definite volume and a highly ordered arrangement where the particles are close together. Liquids also have a definite volume but have a disordered arrangement of particles that are close together. Gases have disordered particles that fill the volume of the container and are far apart from one another.
Solve
In Figure P1.3, two pure diatomic elements (red–red and blue–blue) in the gas phase recombine to form a compound (red–blue) in the solid phase (ordered array of molecules). Therefore, answer b describes the reaction shown.
Think About It
A phase change does not necessarily accompany a chemical reaction. We will learn later that the polarity of the product will determine whether a substance will be in the solid, liquid, or gaseous state at a given temperature.
1.5.
Collect and Organize
From the diagram showing gaseous CO2 at room temperature, we are to describe what the particulate image would be after cooling this gas to 180 K.
Analyze
Looking up the information on the internet for carbon dioxide, CO2(g), we find that it has a sublimation temperature of −78°C or 195 K. This temperature is higher than 180 K. Therefore, CO2 at 180 K will be in the solid phase.
Solve
The particulate image of CO2 at 180 K will show the linear CO2 molecules condensed at the bottom of the box on the right with the molecules touching and forming a regular pattern.
Think About It
Solid CO2 is also known as dry ice, and at normal pressure (1 atm) the only phase change we observe is sublimation, not melting or boiling.
1.7.
Collect and Organize
Using the atomic color palette on the inside back cover of the textbook, we can identify these atoms in these molecules. Chemical formulas describe the type and number of atoms in a molecule.
Analyze
The color palette identifies white atoms as hydrogen, red atoms as oxygen, black atoms as carbon, and green atoms as chlorine. To determine the chemical formula, we indicate the number of each type of atom as a subscript.
Solve
- CH2O
- C2H6O2
- CCl4
Think About It
For carbon-containing compounds, it is standard form to list the atoms in the following order: C, H, N, O.
1.9.
Collect and Organize
Given that the pill manufactured by a pharmaceutical company is to weigh 3.25 mg, we are asked to compare the precision and accuracy of the data in the two graphs of masses of 4 pills.
Analyze
Precision in these pill samples means that the four pills have masses that do not vary much; accuracy in these pill samples means that the four pills, on average, have a mass that is close to the desired mass of 3.25 mg.
Solve
The graph for Sample A shows values that vary, but that are close to the desired value of 3.25 mg—this sample is accurate but not precise. The graph for Sample B shows values that do not vary much, none of which is close to the desired value of 3.25 mg—this sample is precise but not accurate.
Think About It
A sample that was both precise and accurate would show all four pills close in value to each other and all very close to the desired mass of 3.25 mg.
1.11.
Collect and Organize
For this question we are asked to differentiate “hypothesis” from “scientific theory.”
Analyze
These terms are part of the scientific method and result from different aspects of the process of observing and explaining a natural phenomenon.
Solve
A hypothesis is a tentative explanation of an observation or set of observations, whereas a scientific theory is a concise explanation of a natural phenomenon that has been extensively tested and explains why certain phenomena are always observed.
Think About It
Notice that a hypothesis might become a theory after much experimental testing.
1.13.
Collect and Organize
In this question we consider how Dalton’s atomic theory supported his law of multiple proportions.
Analyze
Dalton’s law of multiple proportions states that when two elements combine to make two (or more) compounds, the ratio of the masses of one of the elements, which combine with a given mass of the second element, is always a ratio of small whole numbers. His atomic theory states that matter in the form of elements and compounds is made up of small, indivisible units—atoms.
Solve
Dalton’s atomic theory explained the small, whole-number mass ratios in his law of multiple proportions because the compounds contained small, whole-number ratios of atoms of different elements per molecule or formula unit.
Think About It
Dalton’s theory is not strictly true. Atoms are divisible into electrons, protons, and neutrons (and even further into subatomic quarks), and some compounds do not have whole-number ratios of atoms. For most matter and most compounds that we encounter in chemistry, though, his theory is true.
1.15.
Collect and Organize
In this question we are asked to explain why scientists opposed Proust’s law of definite proportions when he proposed it.
Analyze
The law of definite proportions states that the ratio of elements in a compound is always the same.
Solve
Proust’s law needed to have corroborating evidence to fully support it. At the time, experiments to prepare a compound of tin with oxygen yielded various compositions. The compounds they prepared, when analyzed later, turned out to be mixtures of two compounds of tin oxide.
Think About It
Tin can form either tin(II) oxide, SnO, or tin(IV) oxide, SnO2. What do you think the ratio of the elements would be for a 50–50 mixture of these two compounds? Of a 25–75 mixture?
1.17.
Collect and Organize
We are to define theory as used in everyday conversation and differentiate it from its use in science.
Analyze
Theory in everyday conversation has a quite different meaning from its meaning in science.
Solve
Whereas theory in normal conversation means someone’s idea or opinion that is open to speculation, a scientific theory is a concise and testable explanation of natural phenomena based on observation and experimentation that can accurately predict the results of experiments.
Think About It
Theory in normal conversation is more akin to a hypothesis or a guess that may or may not be testable.
1.19.
Collect and Organize
We are asked to consider whether a scientific hypothesis can be disproven.
Analyze
A scientific hypothesis is a testable, yet tentative, explanation for an observation (or set of observations) in the natural world.
Solve
You can disprove a scientific hypothesis through an experiment that does not give the predicted outcome.
Think About It
An important feature of scientific inquiry that distinguishes it from other forms of inquiry is that the hypotheses are testable and that failure results in a reexamination of the hypotheses.
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