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Questions and Answers
What defines a good hypothesis in scientific research?
What defines a good hypothesis in scientific research?
What is the primary purpose of an experiment in scientific inquiry?
What is the primary purpose of an experiment in scientific inquiry?
Which statement best describes a scientific law?
Which statement best describes a scientific law?
How do scientific theories differ from hypotheses?
How do scientific theories differ from hypotheses?
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What does the Law of Conservation of Mass state?
What does the Law of Conservation of Mass state?
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Which of the following options is an example of a quantitative observation?
Which of the following options is an example of a quantitative observation?
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What characterizes a scientific observation?
What characterizes a scientific observation?
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A valid hypothesis must be capable of being:
A valid hypothesis must be capable of being:
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What defines a pure substance?
What defines a pure substance?
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How do mixtures differ from pure substances?
How do mixtures differ from pure substances?
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Which of the following statements is true about elements?
Which of the following statements is true about elements?
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What characteristic do all samples of a pure substance share?
What characteristic do all samples of a pure substance share?
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In what way can the composition of a mixture change?
In what way can the composition of a mixture change?
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What is a key feature of a pure substance?
What is a key feature of a pure substance?
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Why do mixtures display varying characteristics?
Why do mixtures display varying characteristics?
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What happens to iron atoms in a nail when they rust?
What happens to iron atoms in a nail when they rust?
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Which of the following best describes the nature of elements?
Which of the following best describes the nature of elements?
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Which of the following is a characteristic of physical properties?
Which of the following is a characteristic of physical properties?
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What defines a chemical property?
What defines a chemical property?
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Which of the following is an example of a physical change?
Which of the following is an example of a physical change?
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Which of the following processes is considered a common chemical change?
Which of the following processes is considered a common chemical change?
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The process of subliming involves which of the following?
The process of subliming involves which of the following?
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In the reaction $C_3H_8(g) + 5 O_2(g) \rightarrow 3 CO_2(g) + 4 H_2O(l)$, what type of change is occurring?
In the reaction $C_3H_8(g) + 5 O_2(g) \rightarrow 3 CO_2(g) + 4 H_2O(l)$, what type of change is occurring?
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What distinguishes compounds from elements?
What distinguishes compounds from elements?
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What kind of change occurs when dye fades or changes color?
What kind of change occurs when dye fades or changes color?
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Which statement is true about the molecules in a compound?
Which statement is true about the molecules in a compound?
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What characterizes homogeneous mixtures?
What characterizes homogeneous mixtures?
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Which of the following is NOT a characteristic of heterogeneous mixtures?
Which of the following is NOT a characteristic of heterogeneous mixtures?
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How are all samples of a compound expected to behave?
How are all samples of a compound expected to behave?
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What is a primary component of a compound?
What is a primary component of a compound?
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Which of the following statements about pure substances is true?
Which of the following statements about pure substances is true?
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What is a feature of molecules in a compound?
What is a feature of molecules in a compound?
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What is the primary cause of imprecision in measurements?
What is the primary cause of imprecision in measurements?
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How can systematic errors in measurements be minimized?
How can systematic errors in measurements be minimized?
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Which student demonstrated both accuracy and precision in the measurement of a known mass of 10.00 g?
Which student demonstrated both accuracy and precision in the measurement of a known mass of 10.00 g?
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What determines the accuracy of a measurement?
What determines the accuracy of a measurement?
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Why do systematic errors not average out with repeated measurements?
Why do systematic errors not average out with repeated measurements?
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Which statement accurately describes the nature of random errors?
Which statement accurately describes the nature of random errors?
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What is the result of increasing the precision of a set of measurements?
What is the result of increasing the precision of a set of measurements?
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How do random errors contribute to the overall measurement accuracy?
How do random errors contribute to the overall measurement accuracy?
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What is the first step in solving a conversion problem?
What is the first step in solving a conversion problem?
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Which of the following best describes a conversion factor?
Which of the following best describes a conversion factor?
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When converting inches to centimeters, what should you expect about the size of the resulting number?
When converting inches to centimeters, what should you expect about the size of the resulting number?
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Which relationship is used to convert yards to meters in the provided example?
Which relationship is used to convert yards to meters in the provided example?
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What is the correct way to confirm that the answer to a conversion problem is reasonable?
What is the correct way to confirm that the answer to a conversion problem is reasonable?
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In the example provided, what is the final rounded length in centimeters?
In the example provided, what is the final rounded length in centimeters?
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What does applying the steps in the conceptual plan involve?
What does applying the steps in the conceptual plan involve?
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When is it advisable to work backward in a conversion problem?
When is it advisable to work backward in a conversion problem?
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Study Notes
Chapter 1: Matter, Measurement, and Problem Solving
- Chemistry is a molecular approach, 2nd edition, by Nivaldo Tro.
- The book is authored by Roy Kennedy, from Massachusetts Bay Community College, Wellesley Hills, MA.
- Copyright is 2011 Pearson Education, Inc.
- The chapter focuses on matter, measurement, and problem solving.
Composition of Matter
- Matter is composed of atoms and molecules.
- The scientific method is used to study and understand matter.
Structure Determines Properties
- The properties of matter are determined by the atoms and molecules that compose it.
- Carbon monoxide is composed of one carbon atom and one oxygen atom; it's colorless, odorless, burns with a blue flame, and binds to hemoglobin.
- Carbon dioxide is composed of one carbon atom and two oxygen atoms; it's colorless, odorless, incombustible, and does not bind to hemoglobin.
Atoms and Molecules
- Atoms are submicroscopic particles.
- Molecules are two or more atoms attached together in a specific geometrical arrangement.
- The attachments between atoms are called bonds.
- Bonds have different strengths and come in different shapes and patterns.
- Chemistry is the study of matter.
The Scientific Approach to Knowledge
- Philosophers try to understand the universe through reasoning and thinking about ideal behavior.
- Scientists try to understand the universe through empirical knowledge gained through observation and experiment.
Gathering Empirical Knowledge - Observation
- Some observations describe the characteristics or behavior of nature (qualitative).
- Example: "The soda pop is a liquid with a brown color and a sweet taste. Bubbles are seen floating up through it."
- Some observations compare a characteristic to a standard numerical scale (quantitative).
- Example: "A 240 mL serving of soda pop contains 27 g of sugar."
From Observation to Understanding
- A hypothesis is a tentative interpretation or explanation for an observation.
- A good hypothesis is falsifiable.
- It's possible to prove a hypothesis wrong with one test.
- Example: "The sweet taste of soda pop is due to the presence of sugar."
Testing Ideas
- Ideas in science are tested with experiments.
- An experiment is a set of highly controlled procedures designed to test whether an idea about nature is valid.
- Experiments generate observations that will either validate or invalidate the idea.
From Specific to General Observations
- A scientific law summarizes all past observations and predicts future observations.
- Law of Conservation of Mass: "In a chemical reaction, matter is neither created nor destroyed."
- A scientific law allows prediction of future observations, allowing testing with experiments.
- Unlike state laws, scientific laws are not choices to be violated.
From Specific to General Understanding
- A hypothesis is a potential explanation for a single or small number of observations.
- A scientific theory is a general explanation for why things in nature are the way they are and behave the way they do.
- Theories use models, are the pinnacle of scientific knowledge, and are validated or invalidated by experiment and observation.
Scientific Method
- The scientific method involves observations, experiments, and the development of hypotheses, theories, and laws.
- Observations lead to a hypothesis which tests an idea by conducting experiments that can confirm or falsify that hypothesis.
- Hypotheses that are correct and repeatedly validated through experiments form basis for laws and theories.
Relationships Between Pieces of the Scientific Method
- Observations describe what happens.
- Laws summarize what happens.
- Hypotheses explain why things happen.
- Theories explain why things happen in general.
Classification of Matter
- Matter is anything that occupies space and has mass.
- Matter can be classified by its state (solid, liquid, gas) and its composition.
Classifying Matter by Physical State
- Matter can be classified as solid, liquid, or gas based on observable characteristics.
- Solids have a rigid shape and volume that do not change when placed in a new container; they are not compressible and do not flow.
- Liquids take the shape of their container and maintain their volume; they are not compressible but they flow.
- Gases take both the shape and volume of their containers; they are compressible and flow.
Solids
- The particles are packed closely together and are fixed in position, although they may vibrate.
- The close packing of the particles makes solids incompressible.
- The inability of the particles to move around makes solids retain their shape and volume.
Crystalline Solids
- Some solids have their particles arranged in repeating patterns – called crystalline solids.
Amorphous Solids
- Some solids have their particles arranged randomly distributed without any long-range pattern – called amorphous solids.
Liquids
- The particles in a liquid are closely packed, but they have some ability to move around.
- The close packing means that liquids are incompressible.
- The ability of the particles to move around allows liquids to take the shape of their container and flow.
Gases
- In the gas state, particles have freedom of motion and are not held together.
- The particles are constantly moving around, bumping into each other and the container.
- In a gas there is a lot of empty space between the particles on average.
- Gases are compressible because there is a lot of empty space, particles can be squeezed closer together.
Classifying Matter by Composition
- Another way to classify matter is by examining its composition.
- Composition includes the types of particles, the arrangement of the particles, and the attractions or attachments between them.
- Pure substances, such as elements and compounds, have a fixed composition.
Classification of Pure Substances - Elements
- Pure substances that cannot be decomposed into simpler substances by chemical reactions are called elements.
Classification of Pure Substances - Compounds
- Pure substances that CAN be decomposed into simpler substances are called compounds.
- Compounds are chemical combinations of elements.
- Molecules of a compound are identical.
- All samples of a compound behave the same way.
Classification of Mixtures
- Homogeneous mixtures have uniform composition throughout.
- Heterogeneous mixtures do not have uniform composition throughout.
Changes in Matter
- Changes that alter the state or appearance but not the composition are physical changes.
- Changes that alter the composition are chemical changes.
Physical Changes in Matter
- The boiling of water is a physical change.
- The water molecules are separated, but their structure and composition do not change.
Chemical Changes in Matter
- The rusting of iron is a chemical change.
- The atoms in the nail combine with oxygen to form a new substance called rust, a compound with a different composition.
Properties of Matter
- Physical properties are characteristics that can be changed without changing the composition of matter.
- Chemical properties are characteristics that determine how matter changes composition as a result of contact with other matter, or the influence of energy.
Common Physical Changes
- State changes (boiling, condensing, melting, freezing, subliming)
- Dissolving
Common Chemical Changes
- Rusting
- Burning
- Dyes fading/changing color
Energy
- Matter possesses energy.
- Energy is classified as kinetic or potential.
- Energy is converted between forms during chemical and physical changes.
Energy of Matter - Kinetic Energy
- Kinetic energy is energy of motion.
- Thermal energy (heat) is a form of kinetic energy.
Energy of Matter - Potential Energy
- Potential energy is stored energy.
- Chemical potential energy arises from electrostatic attractive forces between atoms, molecules, and subatomic particles.
Conversion of Energy
- You can interconvert kinetic and potential energy.
- The total amount of energy remains the same regardless of conversion.
Spontaneous Processes
- Materials with high potential energy tend to be less stable.
- Processes in nature tend to occur on their own when the result is material with lower total potential energy.
Changes in Energy
- When a process results in less potential energy, the lost potential energy is converted to kinetic energy and released to the environment.
- Released energy can be harnessed to do work.
Potential to Kinetic Energy
- Conversion of potential energy to kinetic energy can be observed in various mechanisms such as a car running on gasoline.
Standard Units of Measure
- The SI system is a set of international standard units for comparison of measurements.
The Standard Units
- Measurements are expressed using metric units.
Length
- Sl unit is meter.
- Commonly use centimeters.
Mass
- Sl unit is kilogram.
- Commonly measure in grams or milligrams.
Time
- Sl unit is second.
- Defined as period of time for a specific number of radiation events in cesium-133.
Temperature
- Measure of average kinetic energy.
- Heat flows from high to low thermal energy until they reach the same temperature.
Temperature Scales
- Fahrenheit, Celsius, and Kelvin are different temperature scales.
Fahrenheit vs. Celsius
- A Celsius degree is 1.8 times larger than a Fahrenheit degree.
- The standard for 0° on the Fahrenheit scale is a lower temperature than the standard used for 0° on the Celsius scale.
Kelvin vs. Celsius
- The degree size is the same as in Celsius.
- Kelvin begins at absolute zero (much lower than the Celsius scale).
Example: Converting Temperature
- Converting temperatures between Celsius, Kelvin, and Fahrenheit scales involves using specific equations.
Related Units in the SI System
- All SI units are related to a standard unit by a power of 10.
- Prefix multipliers are always the same, regardless of the standard unit.
Common Prefix Multipliers in the SI System
- Common prefix multipliers such as mega-, kilo-, deci-, centi-, milli-, micro-, nano-, and pico- are used in measurement.
Volume
- Derived unit—any length unit cubed.
- Measure of the amount of space occupied.
- Sl unit is cubic meter; commonly use cubic centimeters.
Common Units and Equivalents
- Provides equivalency statements for length, mass, and volume measurements using different units.
Density
- Density is the ratio of mass to volume.
- It is an intensive property.
- For solids = g/cm³.
- For liquids = g/mL.
- For gases = g/L.
Density as a Conversion Factor
- Density can be used to convert between mass and volume.
Example: Calculating Density
- Calculating density for known masses and volumes.
Significant Figures
- Significant figures in measurements tell the range of values to expect for repeated measurements.
- Non-zero digits are always significant.
- Interior zeros (zeros between other digits) are always significant.
- Leading zeros (zeros at the beginning of a number) are never significant.
- Trailing zeros (zeros at the end of a number) are significant only when a decimal point is explicitly shown.
Counting Significant Figures
- Rules for determining the number of significant figures in a measurement, whether exact or estimated.
Significant Figures and Exact Numbers
- Numbers whose values are known with complete certainty are called exact numbers.
- Exact numbers have an unlimited number of significant figures.
Example: Determining Significant Figures
- Demonstrating how to determine the number of significant figures in different measurements.
Practice: Determine Significant Figure
- Exercise involving determining the significant figures in a set of measurements, along with the range of precision.
Multiplication and Division with Significant Figures
- When multiplying or dividing, the result will have the same number of significant figures as the measurement with the fewest significant figures.
Addition and Subtraction with Significant Figures
- When adding or subtracting, the result will have the same number of decimal places as the measurement with the fewest decimal places.
Rounding
- Rules and principles for rounding numbers to the correct number of significant figures.
Precision and Accuracy
- Precision refers to how close repeated measurements are to each other.
- Accuracy refers to how close a measurement is to the actual value.
Uncertainty in Measured Numbers
- Measurements have limitations, leading to uncertainties in the values measured.
Precision
- Imprecision is caused by random errors.
- Random errors result from random fluctuations, so cannot be corrected.
- We evaluate precision of measurements by evaluating how far they are from each other and the actual value.
Accuracy
- Inaccuracy in measurements is caused by systematic errors.
- Systematic errors are caused by limitations in instruments or techniques.
- These errors can be reduced by using more accurate instruments or more refined procedures.
Accuracy vs. Precision
- Examination of how to determine accuracy and precision, as well as how to avoid systematic error.
Solving Chemical Problems; Equations & Dimensional Analysis
- Solving problems using equations and dimensional analysis.
- Units are important when doing calculations as well as the numbers.
- Dimensional analysis provides a guide to problem solving that involves the units in the relationships between different measurements or parameters in calculations.
Problem Solving and Dimensional Analysis
- Many chemistry problems need relationships to convert measurement units.
- Conversion factors can be used to convert between units.
Conceptual Plans
- A visual outline illustrating the methods to a problem.
- Helps understand the steps needed to obtain desired quantities from given quantities.
Conceptual Plans and Conversion Factors
- Procedures to convert units such as inches to centimeters.
- Conversion factors are derived from equivalency statements.
Systematic Approach to Problem Solving
- Steps for solving problems involves sorting information, strategizing (conceptual plan), applying steps in the conceptual plan, and checking the answer with proper units.
Example: Unit Conversion
- Shows the way of performing a unit conversion step-by-step.
- Illustrates examples of problems solved in the conceptual plan.
Practice: Unit Conversion
- Practice converting mL to quarts.
Conceptual Plans for Units Raised to Powers
- Methods for converting a cube unit example: cubic inches to cubic centimeters.
Example: Unit Conversion with Powers
- Shows how to perform a unit conversion step-by-step.
- Illustrates examples of problems solved in the conceptual plan.
Practice: Unit Conversion with Powers
- Demonstrating how to perform unit conversions with raised powers.
Density as a Conversion Factor
- Density is used as a conversion factor between mass and volume.
Example: Density as a Conversion Factor
- How to use density to calculate mass from volume, or volume from mass.
Example: Calculation Using Density
- How to use density as a conversion factor given known mass and volume.
Practice: Calculation Using Density
Order of Magnitude Estimations
- Method for quickly approximating the magnitude of an answer by rounding numbers.
- Emphasizes identifying the proper exponent in scientific notation.
Estimate of Answers
- Approximating the magnitude of answers by rounding during the calculation.
Problem Solving with Equations
- Solving problems that require using equation-based conceptual plans.
- The plan will give all variables except one, then substitute and compute.
Example: Calculating Density using Equations
- Procedure for calculating density when given mass, length and radius.
Practice: Calculating Mass
- Example problems to calculate mass when given density and volume, following an organized approach.
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