unit 1: scientific processes and measurement

Unit 1: Scientific Processes and Measurement

Science: man made pursuit to understand natural phenomena

Chemistry: study of matter

Safety ResourcesHazard Symbols

blue – health red – flammabilityyellow – reactivity white – special

codes

Scale: 0 to 4 0 = no danger4 = extreme danger!

MSDS – Material Safety Data Sheet

• gives important information about chemicals

first aid, fire-fighting, properties, disposal, handling/storage, chemical formula…

Scientific Method•General set of guidelines used in an experiment

Hypothesis•Testable statement based on

observations; can be disproven, but not proven

Which of these is a hypothesis that can be tested through experimentation?

• A) Bacterial growth increases exponentially as temperature increases.

• B) A fish’s ability to taste food is affected by the clarity of aquarium water.

• C) Tadpoles’ fear of carnivorous insect larvae increases as the tadpoles age.

• D) The number of times a dog wags its tail indicates how content the dog is.

Law• States phenomena but does not

address “why?”• Examples: Newton’s Laws of

Motion, Law of Conservation of Mass

Theory• Broad generalization that

explains a body of facts• Summarizes hypotheses that

have been supported through repeated testing

Qualitative ObservationsNon-numerical descriptions in an

experiment

Example: Color is blue…

Quantitative Observations• Observations that are numerical

• Example: the mass is 9.0 grams

Parts of an ExperimentIndependent Variable: variable that is

being changed or manipulated by YOU

Dependent Variable: variable that responds to your change ---- what you see

Controlled Variables: variables that you keep the same

Control or Control Set-up: used for comparison; allows you to measure effects of manipulated variable

Directly proportional: when one variable goes up, the other also goes up

Indirectly proportional: when one variable goes up, the other goes down

The diagram shows different setups of an experiment to determine how sharks find their prey. Which experimental setup is the control?

A) QB) RC) SD) T

• “DRY MIX” - way to remember definitions and graphing

• DRY – dependent, responding, y-axis

• MIX – manipulated, independent, x-axis

Nature of Measurement

Part 1 - Part 1 - numbernumberPart 2 - Part 2 - scale (unit)scale (unit)

Examples:Examples:• 2020 gramsgrams

• 6.63 x 106.63 x 10-34-34 Joule secondsJoule seconds

Measurement - quantitative Measurement - quantitative observation observation consisting of 2 partsconsisting of 2 parts

Measuring Volume Temperature Mass

Reading the Meniscus

Always read volume from the bottom of the meniscus. The meniscus is the curved surface of a liquid in a narrow cylindrical container.

Try to avoid parallax errors.ParallaxParallax errorserrors arise when a meniscus or arise when a meniscus or needle is viewed from an angle rather than needle is viewed from an angle rather than from straight-on at eye level.from straight-on at eye level.

Correct: Viewing the meniscus

at eye level

Incorrect: viewing the meniscus

from an angle

Graduated Cylinders

The glass cylinder has etched marks to indicate volumes, a pouring lip, and quite often, a plastic bumper to prevent breakage.

Measuring Volume Determine the volume contained in a graduated cylinder by reading the bottom of the meniscus at eye level. Read the volume using all certain digits and one uncertain digit.

Certain digits are determined from the calibration marks on the cylinder. The uncertain digit (the last digit of the reading) is estimated.

Use the graduations to find all certain digits

There are two unlabeled graduations below the meniscus, and each graduation represents 1 mL, so the certain digits of the reading are…

52 mL.

Estimate the uncertain digit and take a reading

The meniscus is about eight tenths of the way to the next graduation, so the final digit in the reading is .

The volume in the graduated cylinder is

0.8 mL

52.8 mL.

10 mL GraduateWhat is the volume of liquid in the graduate?

_ . _ _ mL6 26

100mL graduated cylinder What is the volume of liquid in the graduate?

_ _ . _ mL5 2 7

Self TestExamine the meniscus below and determine the volume of liquid contained in the graduated cylinder.

The cylinder contains:

_ _ . _ mL7 6 0

The Thermometero Determine the temperature by reading the scale on the thermometer at eye level.o Read the temperature by using all certain digits and one uncertain digit. o Certain digits are determined from the

calibration marks on the thermometer. o The uncertain digit (the last digit of the reading) is estimated. o On most thermometers encountered in a general chemistry lab, the tenths place is the uncertain digit.

Do not allow the tip to touch the walls or the bottom of the flask.

If the thermometer bulb touches the flask, the temperature of the glass will be measured instead of the temperature of the solution. Readings may be incorrect, particularly if the flask is on a hotplate or in an ice bath.

Reading the ThermometerDetermine the readings as shown below on Celsius thermometers:

_ _ . _ C _ _ . _ C8 7 4 3 5 0

Measuring Mass - The Beam Balance

Our balances have 4 beams – the uncertain digit is the thousandths place ( _ _ _ . _ _ X)

Balance Rules In order to protect the balances and ensure accurate results, a number of rules should be followed:

Always check that the balance is level and zeroed before using it. Never weigh directly on the balance pan. Always use a piece of weighing paper to protect it. Do not weigh hot or cold objects. Clean up any spills around the balance immediately.

Mass and Significant Figureso Determine the mass by reading the riders on the beams at eye level.o Read the mass by using all certain digits and one uncertain digit.

oThe uncertain digit (the last digit of the reading) is estimated. o On our balances, the hundredths place is uncertain.

Determining Mass 1. Place

object on pan

2. Move riders along beam, starting with the largest, until the pointer is at the zero mark

Check to see that the balance scale is at zero

Read Mass

_ _ _ . _ _ _1 1 4 ? ? ?

Read Mass More Closely

_ _ _ . _ _ _1 1 4 4 9 7

Uncertainty in Measurement

• A A digit that must be digit that must be estimatedestimated is is called called uncertainuncertain. A . A measurementmeasurement always has some degree of uncertainty.always has some degree of uncertainty.

Why Is there Uncertainty? Measurements are performed with instruments No instrument can read to an infinite number of decimal placesWhich of these balances has the greatest

uncertainty in measurement?

Precision and AccuracyAccuracy Accuracy refers to the agreement of a refers to the agreement of a

particular value with the particular value with the truetrue value.value.

PrecisionPrecision refers to the degree of agreement refers to the degree of agreement among several measurements made in among several measurements made in the same manner.the same manner.

Neither accurate nor

precise

Precise but not accurate

Precise AND accurate

Rules for Counting Significant Figures - Details

• Nonzero integersNonzero integers always always count as significant figures.count as significant figures.

• 34563456 hashas • 44 sig figs.sig figs.

Rules for Counting Significant Figures - Details

• ZerosZeros• Leading zerosLeading zeros do not count as do not count as

significant figuressignificant figures..

• 0.04860.0486 has has• 33 sig figs. sig figs.

Rules for Counting Significant Figures - Details

• ZerosZerosCaptive zerosCaptive zeros always count asalways count as

significant figures.significant figures.

• 16.0716.07 hashas• 4 4 sig figs.sig figs.

Rules for Counting Significant Figures - Details

• ZerosZeros• Trailing zerosTrailing zeros are significant are significant

only if the number contains a only if the number contains a decimal point.decimal point.

• 9.3009.300 has has• 44 sig figs. sig figs.

Rules for Counting Significant Figures - Details

• Exact numbersExact numbers have an infinite have an infinite number of significant figures.number of significant figures.

• 11 inch = inch = 2.542.54 cm, exactlycm, exactly

Sig Fig Practice #1How many significant figures in each of the following?1.0070 m

5 sig figs

17.10 kg 4 sig figs

100,890 L 5 sig figs

3.29 x 103 s 3 sig figs0.0054 cm 2 sig figs3,200,000 2 sig figs

Rules for Significant Figures in Mathematical Operations

• Multiplication and DivisionMultiplication and Division:: # sig # sig figs in the result equals the number figs in the result equals the number in the least precise measurement in the least precise measurement used in the calculation.used in the calculation.

• 6.38 x 6.38 x 2.02.0 = =• 12.76 12.76 13 (2 sig figs)13 (2 sig figs)

Sig Fig Practice #2

3.24 m x 7.0 mCalculation Calculator says: Answer

22.68 m2 23 m2

100.0 g ÷ 23.7 cm3 4.219409283 g/cm3 4.22 g/cm3

0.02 cm x 2.371 cm 0.04742 cm2 0.05 cm2

710 m ÷ 3.0 s 236.6666667 m/s 240 m/s1818.2 lb x 3.23 ft 5872.786 lb·ft 5870 lb·ft

1.030 g ÷ 2.87 mL 2.9561 g/mL 2.96 g/mL

Rules for Significant Figures in Mathematical Operations

• Addition and SubtractionAddition and Subtraction: The : The number of decimal places in the result number of decimal places in the result equals the number of decimal places equals the number of decimal places in the least precise measurement.in the least precise measurement.

• 6.8 + 11.934 =6.8 + 11.934 =• 18.734 18.734 18.7 ( 18.7 (3 sig figs3 sig figs))

Sig Fig Practice #3

3.24 m + 7.0 mCalculation Calculator says: Answer

10.24 m 10.2 m100.0 g - 23.73 g 76.27 g 76.3 g

0.02 cm + 2.371 cm 2.391 cm 2.39 cm713.1 L - 3.872 L 709.228 L 709.2 L1818.2 lb + 3.37 lb 1821.57 lb 1821.6

lb2.030 mL - 1.870 mL 0.16 mL 0.160 mL

In science, we deal with some In science, we deal with some very very LARGELARGE numbers: numbers:

1 mole = 6020000000000000000000001 mole = 602000000000000000000000

In science, we deal with some In science, we deal with some very very SMALLSMALL numbers: numbers:

Mass of an electron =Mass of an electron =0.000000000000000000000000000000091 kg0.000000000000000000000000000000091 kg

Scientific NotationScientific Notation

Imagine the difficulty of Imagine the difficulty of calculating the mass of 1 mole calculating the mass of 1 mole of electrons!of electrons!

0.00000000000000000000000000000000.000000000000000000000000000000091 kg91 kg x 602000000000000000000000x 602000000000000000000000

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Scientific Scientific Notation:Notation:A method of representing very large A method of representing very large

or very small numbers in the or very small numbers in the form:form:

M x 10nM x 10n MM is a number between is a number between 11 and and 1010 nn is an integer is an integer

2 500 000 000

Step #1: Insert an understood decimal pointStep #1: Insert an understood decimal point

.Step #2: Decide where the decimal Step #2: Decide where the decimal must end must end up so that one number is to its up so that one number is to its leftleftStep #3: Count how many places you Step #3: Count how many places you bounce bounce the decimal pointthe decimal point

123456789

Step #4: Re-write in the form M x 10Step #4: Re-write in the form M x 10nn

2.5 x 102.5 x 1099

The exponent is the number of places we moved the decimal.

0.00005790.0000579

Step #2: Decide where the decimal Step #2: Decide where the decimal must end must end up so that one number is to its up so that one number is to its leftleftStep #3: Count how many places you Step #3: Count how many places you bounce bounce the decimal pointthe decimal pointStep #4: Re-write in the form M x 10Step #4: Re-write in the form M x 10nn

1 2 3 4 5

5.79 x 105.79 x 10-5-5

The exponent is negative because the number we started with was less than 1.

ReviewReview::Scientific notation Scientific notation expresses a number in the expresses a number in the form:form: M x 10M x 10nn

1 1 M M 1010

n is an n is an integerinteger

Calculator instructions

2 x 106 is entered as 2 2nd EE 6EE means x 10

If you see E on your calculator screen, it also means x 10

Try…

2 x 1014 / 3 x 10-3 = ?

2 x 10-34 x 3 x 1023

4.5 x 1023 / 5.26 x 10-14

The Fundamental SI Units (le Système International, SI)

Physical Quantity Name Abbreviation Mass kilogram kg Length meter m Time second s Temperature Kelvin K Volume Liter L Amount of Substance mole mol

Metric System Prefixes (use with standard base units)

Kilo 103 1000 KINGHecta 102 100 HENRYDeca 101 10 DIEDUnit 100 1

UNEXPECTEDLYDeci 10-1 0.1 DRINKINGCenti 10-2 0.01 CHOCOLATEMilli 10-3 0.001 MILK

Conversion Unit Examples

1 L = 1000 mL 1 Hm = ______ m

1 m = ____ cm 1 Dm = _____ m

1 kg = 1000 g ___ dm = 1 m

Metric System Prefixes (use with standard base units)

Tera 1012 1,000,000,000,000 THEGiga 109 1,000,000,000 GREATMega 106 1,000,000 MIGHTYKilo 103 1000 KINGHecta 102 100 HENRYDeca 101 10 DIEDUnit 100 1 UNEXPECTEDLYDeci 10-1 0.1 DRINKINGCenti 10-2 0.01 CHOCOLATEMilli 10-3 0.001 MILKMicro 10-6 0.000001 MAYBENano 10-9 0.000000001 NOTPico 10-12 0.000000000001 PASTUERIZED?

Conversion Unit Examples

1 L = 1000 mL 1 m = ______ nm

1 m = ____ cm 1 Dm = _____ m

1 kg = 1000 g ___ dm = 1 m

1 Mm = _____ m1 Gb = _____ byte