Unit 1: Scientific Processes and Measurement

Science: man made pursuit to understand natural phenomena Chemistry: study of matter

Safety Resources Hazard Symbols blue – healthred – flammability yellow – reactivitywhite – special codes Scale: 0 to 4 0 = no danger 4 = 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 Observations Non-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 Experiment Independent 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) Q B) R C) S D) T

“DRY MIX” - way to remember definitions and graphing DRY – dependent, responding, y-axis MIX – manipulated, independent, x-axis

Nature of Measurement Part 1 - number Part 2 - scale (unit) Examples: 20 grams20 grams 6.63 x Joule seconds6.63 x Joule seconds Measurement - quantitative observation consisting of 2 parts consisting 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. Parallax errors arise when a meniscus or needle is viewed from an angle rather than 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 Graduate What is the volume of liquid in the graduate? _. _ _ mL 6 2 6

100mL graduated cylinder What is the volume of liquid in the graduate? _ _. _ mL 527

Self Test Examine the meniscus below and determine the volume of liquid contained in the graduated cylinder. The cylinder contains: _ _. _ mL 760

The Thermometer o 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 Thermometer Determine the readings as shown below on Celsius thermometers: _ _. _  C

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 Figures o 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 _ _ _. _ _ _ 114? ? ?

Read Mass More Closely _ _ _. _ _ _

Uncertainty in Measurement A digit that must be estimated is called uncertain. A measurement always has some degree of uncertainty.A digit that must be estimated is called uncertain. A measurement 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 places Which of these balances has the greatest uncertainty in measurement?

Precision and Accuracy Accuracy refers to the agreement of a particular value with the true value. Precision refers to the degree of agreement among several measurements made in the same manner. Neither accurate nor precise Precise but not accurate Precise AND accurate

Rules for Counting Significant Figures - Details Nonzero integers always count as significant figures has3456 has 4 sig figs.4 sig figs.

Rules for Counting Significant Figures - Details ZerosZeros Leading zeros do not count asLeading zeros do not count as significant figures has has 3 sig figs.3 sig figs.

Rules for Counting Significant Figures - Details ZerosZeros Captive zeros always count as significant figures has16.07 has 4 sig figs.4 sig figs.

Rules for Counting Significant Figures - Details ZerosZeros Trailing zeros are significant only if the number contains a decimal point.Trailing zeros are significant only if the number contains a decimal point has9.300 has 4 sig figs.4 sig figs.

Rules for Counting Significant Figures - Details Exact numbers have an infinite number of significant figures. 1 inch = 2.54 cm, exactly1 inch = 2.54 cm, exactly

Sig Fig Practice #1 How many significant figures in each of the following? m  5 sig figs kg  4 sig figs 100,890 L  5 sig figs 3.29 x 10 3 s  3 sig figs cm  2 sig figs 3,200,000  2 sig figs

Rules for Significant Figures in Mathematical Operations Multiplication and Division: # sig figs in the result equals the number in the least precise measurement used in the calculation x 2.0 =6.38 x 2.0 =  13 (2 sig figs)12.76  13 (2 sig figs)

Sig Fig Practice # m x 7.0 m CalculationCalculator says:Answer m 2 23 m g ÷ 23.7 cm g/cm g/cm cm x cm cm cm m ÷ 3.0 s m/s240 m/s lb x 3.23 ft lb·ft 5870 lb·ft g ÷ 2.87 mL g/mL2.96 g/mL

Rules for Significant Figures in Mathematical Operations Addition and Subtraction: The number of decimal places in the result equals the number of decimal places in the least precise measurement.Addition and Subtraction: The number of decimal places in the result equals the number of decimal places in the least precise measurement = =  18.7 (3 sig figs)  18.7 (3 sig figs)

Sig Fig Practice # m m CalculationCalculator says:Answer m 10.2 m g g g 76.3 g 0.02 cm cm cm 2.39 cm L L L709.2 L lb lb lb lb mL mL 0.16 mL mL

In science, we deal with some very LARGE numbers: 1 mole = In science, we deal with some very SMALL numbers: Mass of an electron = kg Scientific Notation

Imagine the difficulty of calculating the mass of 1 mole of electrons! kg x x ???????????????????????????????????

Scientific Notation: A method of representing very large or very small numbers in the form: M x 10n M x 10n  M is a number between 1 and 10  n is an integer

Step #1: Insert an understood decimal point. Step #2: Decide where the decimal must end up so that one number is to its left up so that one number is to its left Step #3: Count how many places you bounce the decimal point the decimal point Step #4: Re-write in the form M x 10 n

2.5 x 10 9 The exponent is the number of places we moved the decimal.

Step #2: Decide where the decimal must end up so that one number is to its left up so that one number is to its left Step #3: Count how many places you bounce the decimal point the decimal point Step #4: Re-write in the form M x 10 n 12345

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

Review: Scientific notation expresses a number in the form: M x 10 n 1  M  10 n is an integer

Calculator instructions 2 x 10 6 is entered as 2 2 nd EE 6 EE means x 10 If you see E on your calculator screen, it also means x 10

Try… 2 x / 3 x = ? 2 x x 3 x x / 5.26 x

The Fundamental SI Units (le Système International, SI)

Metric System Prefixes (use with standard base units) Kilo KING Hecta HENRY Deca DIED Unit UNEXPECTEDLY Deci DRINKING Centi CHOCOLATE Milli MILK

Conversion Unit Examples 1 L = 1000 mL1 Hm = ______ m 1 m = ____ cm1 Dm = _____ m 1 kg = 1000 g___ dm = 1 m

Metric System Prefixes (use with standard base units) Tera ,000,000,000,000THE Giga10 9 1,000,000,000GREAT Mega10 6 1,000,000MIGHTY Kilo KING Hecta HENRY Deca DIED Unit UNEXPECTEDLY Deci DRINKING Centi CHOCOLATE Milli MILK Micro MAYBE Nano NOT Pico PASTUERIZED?

Conversion Unit Examples 1 L = 1000 mL1 m = ______ nm 1 m = ____ cm1 Dm = _____ m 1 kg = 1000 g___ dm = 1 m 1 Mm = _____ m1 Gb = _____ byte