The Methods of Science and the Properties of Matter

The Methods of Science and the Properties of Matter
Unit 1 The Methods of Science and the Properties of Matter

Part 1 Essential Questions
What are the common steps of scientific methods? What are the variables and the controls in an experiment? What is the difference between a scientific theory and a scientific law? Copyright © McGraw-Hill Education Scientific Methods

A Systematic Approach Scientific methods are systematic approaches used in scientific study, whether it is chemistry, physics, biology, or another science. They are organized processes used by scientists to do research, and provide methods for scientists to verify the work of others. The steps in a scientific method are repeated until a hypothesis is supported or discarded. Copyright © McGraw-Hill Education Scientific Methods

A Systematic Approach An observation is the act of gathering information. Qualitative data is obtained through observations that describe color, smell, shape, or some other physical characteristic that is related to the five senses. Quantitative data is obtained from numerical observations that describe how much, how little, how big or how fast. A hypothesis is a tentative explanation for what has been observed. An experiment is a set of controlled observations that test the hypothesis. Copyright © McGraw-Hill Education Scientific Methods

A Systematic Approach A variable is a quantity or condition that can have more than one value. An independent variable is the variable you plan to change. The dependent variable is the variable that changes in value in response to a change in the independent variable. If you were trying to determine if temperature affects bacterial growth, you would expose different petri dishes of the same bacteria to different temperatures. Temperature is your independent variable. Bacteria growth is your dependent variable. Copyright © McGraw-Hill Education Scientific Methods

A Systematic Approach A control is a standard for comparison in the experiment. During clinical drug trials, physicians will use a double-blind study. They use two statistically identical groups of patients. One will receive the drug and one will receive a placebo. Neither patient or physician will know which group receives the drug. The group receiving the placebo is the control group. A conclusion is a judgment based on the information obtained from the experiment. A hypothesis is never proven, only supported or discarded. Copyright © McGraw-Hill Education Scientific Methods

Theory and Scientific Law
A scientific theory is an explanation that has been repeatedly supported by many experiments. A theory states a broad principle of nature that has been supported over time by repeated testing. Theories are successful if they can be used to make predictions that are true. A scientific law is a relationship in nature that is supported by many experiments, and no exceptions to these relationships are found. Copyright © McGraw-Hill Education Scientific Methods

What are the SI base units for time, length, mass, and temperature? How does adding a prefix change a unit? How are the derived units different for volume and density? How do accuracy and precision compare? How can the accuracy of data be described using error and percent error? How do we take proper measurements? Why are graphs created? How can graphs be interpreted? Copyright © McGraw-Hill Education Scientific Methods

Units of Measurement Base Units
Système Internationale d'Unités (SI) is an internationally agreed upon system of measurements. A base unit is a defined unit in a system of measurement that is based on an object or event in the physical world, and is independent of other units. To better describe the range of possible measurements, scientists add prefixes to the base units. The prefixes (seen in the table on the next slide) are based on factors of ten and can be used with all SI units. Units and Measurements Copyright © McGraw-Hill Education

SI (Metric) Prefixes Units and Measurement
Copyright © McGraw-Hill Education Units and Measurement

Base Units and SI Prefixes
The SI base unit of time is the second (s), based on the frequency of radiation given off by a cesium-133 atom. The SI base unit for length is the meter (m), the distance light travels in a vacuum in 1/299,792,458th of a second. The SI base unit of mass is the kilogram (kg), about 2.2 pounds. The SI base unit of temperature is the kelvin (K). Zero kelvin is the point where there is virtually no particle motion or kinetic energy, also known as absolute zero. Two other temperature scales are Celsius and Fahrenheit. Copyright © McGraw-Hill Education Units and Measurements

Derived Units Not all quantities can be measured with SI base units. A unit that is defined by a combination of base units is called a derived unit. Example: The SI unit for speed is meters per second (m/s). Another quantity that is measured in derived units is volume (cm3), measured in cubic meters. The three cubes show volume relationships between cubic meters (m3), cubic decimeters (dm3), cubic centimeters (cm3), and cubic millimeters (mm3). Units and Measurements Copyright © McGraw-Hill Education

Derived Units The cubic meter is a large volume that is difficult to work with. For everyday use, a more useful unit of volume is the liter. A liter (L) is equal to one cubic decimeter (dm3), that is, 1 L equals 1 dm3. Density is another derived unit, g/cm3, the amount of mass per unit volume. The density of a substance usually cannot be measured directly. Rather, it is calculated using mass and volume measurements. You can calculate density using the following equation: density = mass/volume Copyright © McGraw-Hill Education Units and Measurements

Measurement in the scientific method
The key to a good experiment is being able to make good measurements and record our data in the proper way. If we do not make good measurements, we will have incorrect data. Incorrect data results in bad results and wrong conclusions.

Accuracy and Precision
Accuracy refers to how close a measured value is to an accepted value. Precision refers to how close a series of measurements are to one another. Copyright © McGraw-Hill Education Uncertainty in Data

Error is defined as the difference between an experimental value and an accepted value. a: These trial values are the most precise b: This average is the most accurate Uncertainty in Data Copyright © McGraw-Hill Education

Error ALL MEASUREMENTS HAVE ERROR So what is error?
Error is a measure of how far off you are from correct Error depends on a number of different factors, but the main source of error is the tools we use to make the measurements The accuracy of a measurement is dependent upon the tools we use to make the measurement.

Error When recording our measurement, we have to make a guess…the guess shows our error…the smaller the guess, the more accurate our measurement… How long is the box? I know the measurement is at least 5 cm… cm But since there are not marks between the centimeters, that is all we know for sure… So we guess…5.8cm, the last digit shows our guess Since each person guesses different, the last digit shows our error

Error To Get less error, we use a tool with smaller guesses…
What is the measurement with a more accurate tool? 5.91 cm…the 1 is a guess

Minimizing Error There are many ways to minimize your error in measurement, but the main ways are… Using more accurate tools – since your measurement can only be as accurate as your tool, if your tool is more accurate, your measurement will be more accurate. Avoiding parallax – parallax is the apparent shift in location due to the position of an observer… We avoid parallax by…(volunteers needed for demonstration)

Graphing A graph is a visual display of data that makes trends easier to see than in a table. A circle graph, or pie chart, has wedges that visually represent percentages of a fixed whole. Copyright © McGraw-Hill Education Representing Data

Graphing On line graphs, independent variables are plotted on the x-axis and dependent variables are plotted on the y-axis. If a line through the points is straight, the relationship is linear and can be analyzed further by examining the slope. Copyright © McGraw-Hill Education Representing Data

Interpreting Graphs Interpolation is reading and estimating values falling between points on the graph. Extrapolation is estimating values outside the points by extending the line. This graph shows important ozone measurements and helps the viewer visualize a trend from two different time periods. Copyright © McGraw-Hill Education Representing Data

What are the rules for significant figures and how can they be used to express uncertainty in measured and calculated values? Why (and how) do we use scientific notation to express numbers? Copyright © McGraw-Hill Education Uncertainty in Data

Significant Figures As discussed previously, precision is often limited by the tools available. Significant figures include all known digits plus one estimated digit. Copyright © McGraw-Hill Education Uncertainty in Data

Significant Figures Rules for significant figures:
Rule 1: Nonzero numbers are always significant. Rule 2: Zeros between nonzero numbers are always significant. Rule 3: All final zeros to the right of the decimal are significant. Rule 4: Placeholder zeros are not significant. To remove placeholder zeros, rewrite the number in scientific notation. Rule 5: Counting numbers and defined constants have an infinite number of significant figures. Copyright © McGraw-Hill Education Uncertainty in Data

Significant Figures So, is there an easy way to figure this out without memorizing the rules… YES! – but you should still know the rules since you don’t get this little trick on test day

Sig Fig Tool We will use our great nation to identify the sig figs in a number… On the left of the US is the Pacific and on the right is the Atlantic P A

Sig Fig Tool If we write our number in the middle of the country we can find the number of sig figs by starting on the correct side of the country… If the decimal is Present, we start on the Pacific side If the decimal is Absent, we start on the Atlantic side We then count from the first NON zero till we run out of digits… P A

Sig Fig Tool Examples P 105200 A 4 This number has _____ sig figs

Sig Fig Tool Examples P A 6 This number has _____ sig figs

Rounding Numbers Calculators are not aware of significant figures. Answers should not have more significant figures than the original data with the fewest figures, and should be rounded. Rules for rounding: Rule 1: If the digit to the right of the last significant figure is less than 5, do not change the last significant figure → 2.53 Rule 2: If the digit to the right of the last significant figure is greater than 5, round up the last significant figure → 2.54 Rule 3: If the digits to the right of the last significant figure are a 5 followed by a nonzero digit, round up the last significant figure → 2.54 Rule 4: If the digits to the right of the last significant figure are a 5 followed by a 0 or no other number at all, look at the last significant figure. If it is odd, round it up; if it is even, do not round up → 2.54 → 2.52 Copyright © McGraw-Hill Education Uncertainty in Data

Rounding Numbers Addition and subtraction
Round the answer to the same number of decimal places as the original measurement with the fewest decimal places. Multiplication and division Round the answer to the same number of significant figures as the original measurement with the fewest significant figures. Copyright © McGraw-Hill Education Uncertainty in Data

ROUNDING NUMBERS WHEN ADDING
SOLVE FOR THE UNKNOWN Align the measurements and add the values. 28.0 cm cm cm cm Round to one place after the decimal; Rule 1 applies. The answer is 77.2 cm. Use with Example Problem 7. Problem A student measured the length of his lab partners’ shoes. If the lengths are cm, cm, and cm, what is the total length of the shoes? Response ANALYZE THE PROBLEM The three measurements need to be aligned on their decimal points and added. The measurement with the fewest digits after the decimal point is 28.0 cm, with one digit. Thus, the answer must be rounded to only one digit after the decimal point. EVALUATE THE ANSWER The answer, 77.2 cm, has the same precision as the least-precise measurement, 28.0 cm. Copyright © McGraw-Hill Education Uncertainty in Data

Volume = length × width × height
ROUNDING NUMBERS WHEN MULTIPLYING SOLVE FOR THE UNKNOWN Calculate the volume, and apply the rules of significant figures and rounding. State the formula for the volume of a rectangle. Volume = length × width × height Substitute values and solve. Volume = 28.3 cm × 22.2 cm × 3.65 cm = cm3 Round the answer to three significant figures. Volume = 2290 cm3 Use with Example Problem 8. Problem Calculate the volume of a book with the following dimensions: length = 28.3 cm, width = 22.2 cm, height = 3.65 cm. Response ANALYZE THE PROBLEM Volume is calculated by multiplying length, width, and height. Because all of the measurements have three significant figures, the answer also will. EVALUATE THE ANSWER To check if your answer is reasonable, round each measurement to one significant figure and recalculate the volume. Volume = 30 cm × 20 cm × 4 cm = 2400 cm3. Because this value is close to your calculated value of 2290 cm3, it is reasonable to conclude the answer is correct. KNOWN UNKNOWN Length = 28.3 cm Volume = ? cm3 Width = 22.2 cm Height = 3.65 cm Copyright © McGraw-Hill Education Uncertainty in Data

Scientific Notation Scientific notation can be used to express any number as a number between 1 and 10 (known as the coefficient) multiplied by 10 raised to a power (known as the exponent). Carbon atoms in the Hope Diamond = 4.6 x 1023 4.6 is the coefficient and 23 is the exponent. Count the number of places the decimal point must be moved to give a coefficient between 1 and 10. The number of places moved equals the value of the exponent. The exponent is positive when the decimal moves to the left and negative when the decimal moves to the right. 800 = 8.0 × 102 = 3.43 × 10–5 Copyright © McGraw-Hill Education Scientific Notation and Dimensional Analysis

Scientific Notation Problem Response SOLVE FOR THE UNKNOWN
Move the decimal point to give a coefficient between 1 and 10. Count the number of places the decimal point moves, and note the direction. Move the decimal point six places to the left. Move the decimal point eight places to the right. Write the coefficients, and multiply them by 10n where n equals the number of places moved. When the decimal point moves to the left, n is positive; when the decimal point moves to the right, n is negative. Add units to the answers. a × 106 km b. 2.8 × 10-8 g/cm3 Use with Example Problem 2. Problem Write the following data in scientific notation. a. The diameter of the Sun is 1,392,000 km. b. The density of the Sun’s lower atmosphere is g/cm3 . Response ANALYZE THE PROBLEM You are given two values, one much larger than 1 and the other much smaller than 1. In both cases, the answers will have a coefficient between 1 and 10 multiplied by a power of 10. Scientific Notation and Dimensional Analysis Copyright © McGraw-Hill Education

Scientific Notation EVALUATE THE ANSWER
The answers are correctly written as a coefficient between 1 and 10 multiplied by a power of 10. Because the diameter of the Sun is a number greater than 1, its exponent is positive. Because the density of the Sun’s lower atmosphere is a umber less than 1, its exponent is negative. Copyright © McGraw-Hill Education Scientific Notation and Dimensional Analysis

Dimensional Analysis Dimensional analysis is a systematic approach to problem solving that uses conversion factors to move, or convert, from one unit to another. A conversion factor is a ratio of equivalent values having different units. Writing conversion factors: Conversion factors are derived from equality relationships, such as 1 dozen eggs = 12 eggs. Percentages can also be used as conversion factors. They relate the number of parts of one component to 100 total parts. Using conversion factors: A conversion factor must cancel one unit and introduce a new one. Copyright © McGraw-Hill Education Scientific Notation and Dimensional Analysis

USING CONVERSION FACTORS
KNOWN UNKNOWN Length = 6 Egyptian cubits length= ? g 7 palms = 1 cubit 1 palm = 4 fingers 1 finger = mm 1 m = 1000 mm Use with Example Problem 4. Problem In ancient Egypt, small distances were measured in Egyptian cubits. An Egyptian cubit was equal to 7 palms, and 1 palm was equal to 4 fingers. If 1 finger was equal to mm, convert 6 Egyptian cubits to meters. SOLVE FOR THE UNKNOWN Use dimensional analysis to convert the units in the following order. cubits → palms → fingers → millimeters → meters Multiply by a series of conversion factors that cancels all the units except meter, the desired unit. 6 cubits× 7 palms 1 cubit × 4 fingers 1 palm × mm 1 finger × 1 meter 1000 mm = ? m Response ANALYZE THE PROBLEM A length of 6 Egyptian cubits needs to be converted to meters. Units and Measurements Copyright © McGraw-Hill Education

USING CONVERSION FACTORS
SOLVE FOR THE UNKNOWN 6 cubits× 7 palms 1 cubit × 4 fingers 1 palm × mm 1 finger × 1 meter 1000 mm = m EVALUATE THE ANSWER Each conversion factor is a correct restatement of the original relationship, and all units except for the desired unit, meters, cancel. Units and Measurements Copyright © McGraw-Hill Education

What characteristics identify a substance? What distinguishes physical properties from chemical properties? How do the properties of the physical states of matter differ? Copyright © McGraw-Hill Education Properties of Matter

Substances Matter is anything that has mass and takes up space. Matter is everything around us. Matter with a uniform and unchanging composition is a substance. Much of your chemistry course will be focused on the composition of substances and how they interact with one another. Copyright © McGraw-Hill Education Properties of Matter

States of Matter The physical forms of matter, either solid, liquid, or gas, are called the states of matter. Solids are a form of matter that have their own definite shape and volume. Liquids are a form of matter that have a definite volume but take the shape of the container. Properties of Matter Copyright © McGraw-Hill Education

States of Matter Gases have no definite shape or volume. They expand to fill their container. Vapor refers to the gaseous state of a substance that is a solid or liquid at room temperature. Properties of Matter Copyright © McGraw-Hill Education

Physical Properties of Matter
A physical property is a characteristic that can be observed or measured without changing the sample’s composition. Copyright © McGraw-Hill Education Properties of Matter

Physical Properties of Matter
Extensive properties, such as mass, length, and volume, are dependent on the amount of substance present. Intensive properties, such as density, are dependent on the what the substance is not how much there is. Copyright © McGraw-Hill Education Properties of Matter

Chemical Properties of Matter
The ability of a substance to combine with or change into one or more other substances is called a chemical property. Examples include: Iron forming rust Copper turning green in the air Copyright © McGraw-Hill Education Properties of Matter

Observing Properties of Matter
A substance can change form—an important concept in chemistry. Both physical and chemical properties can change with specific environmental conditions, such as temperature and pressure. Copyright © McGraw-Hill Education Properties of Matter

What is a physical change and what are several common examples? What defines a chemical change? How can you recognize a chemical change? How does the law of conservation of mass apply to chemical reactions? Copyright © McGraw-Hill Education Changes in Matter

Physical Changes A change that alters a substance without changing its composition is known as a physical change. A phase change is a transition of matter from one state to another. Boiling, freezing, melting, and condensing all describe phase changes in chemistry. Copyright © McGraw-Hill Education Changes in Matter

Chemical Changes A change that involves one or more substances turning into new substances is called a chemical change. Decomposing, rusting, exploding, burning, or oxidizing are all terms that describe chemical changes. Copyright © McGraw-Hill Education Changes in Matter

Law of Conservation of Mass
The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction, it is conserved. The mass of the reactants equals the mass of the products. massreactants = massproducts Copyright © McGraw-Hill Education Changes in Matter

CONSERVATION OF MASS Problem Response KNOWN UNKNOWN
mmercury(II) oxide = g moxygen = ? g mmercury = 9.26 g Use with Example Problem 1. Problem In an experiment, g of red mercury(II) oxide powder is placed in an open flask and heated until it is converted to liquid mercury and oxygen gas. The liquid mercury has a mass of 9.26 g. What is the mass of oxygen formed in the reaction? SOLVE FOR THE UNKNOWN State the law of conservation of mass. Massreactants = Massproducts mmercury(II) oxide = mmercury + moxygen Solve for m oxygen. moxygen = mmercury(II) oxide − mmercury Substitute mmercury(II) oxide = g and mmercury = 9.26 g. moxygen = g − 9.26 g moxygen = 0.74 g Response ANALYZE THE PROBLEM You are given the mass of a reactant and the mass of one of the products in a chemical reaction. According to the law of mass conservation, the total mass of the products must equal the total mass of the reactants. Section Title Copyright © McGraw-Hill Education

CONSERVATION OF MASS EVALUATE THE ANSWER
The sum of the masses of the two products equals the mass of the reactant, verifying that mass has been conserved. The answer is correctly expressed to the hundredths place, making the number of significant digits correct. Copyright © McGraw-Hill Education Section Title

All information and skills in this unit will be on the unit 1 test.
End of Unit 1

The Methods of Science and the Properties of Matter

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