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Scientific Measurement Chemistry chapter 2

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Scientific Measurement Distinguish between quantitative and qualitative measurements. Distinguish between quantitative and qualitative measurements. List SI units of measurement and common SI prefixes. List SI units of measurement and common SI prefixes. Distinguish between the mass and weight of an object. Distinguish between the mass and weight of an object. Convert measurement to scientific notation. Convert measurement to scientific notation. Distinguish among the accuracy, precision, and error of measurement. Distinguish among the accuracy, precision, and error of measurement. Identify the number of significant figures in a measurement and in the result of calculation. Identify the number of significant figures in a measurement and in the result of calculation. Identify and calculate derived units. Identify and calculate derived units. Calculate the density of an object from experiment data. Calculate the density of an object from experiment data. TEKS: 2A, 2B, 2C, 2D, 2E, 3C, 3D, 3E, 4B, 4C

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Branches of chemistry organic chemistrythe study of carbon-containing compounds organic chemistrythe study of carbon-containing compounds inorganic chemistrythe study of non-organic substances inorganic chemistrythe study of non-organic substances physical chemistrythe study of properties of matter, changes that occur in matter, and the relationships between matter and energy physical chemistrythe study of properties of matter, changes that occur in matter, and the relationships between matter and energy analytical chemistrythe identification of the composition of materials analytical chemistrythe identification of the composition of materials biochemistrythe study of the chemistry of living things biochemistrythe study of the chemistry of living things theoretical chemistrythe use of mathematics and computers to design and predict the properties of new compounds theoretical chemistrythe use of mathematics and computers to design and predict the properties of new compounds

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Quantitative vs. Qualitative Observations Qualitative – observations made with adjectives Qualitative – observations made with adjectives The water is clear and cool. Quantitative – observations that include a measurement or other numeric data Quantitative – observations that include a measurement or other numeric data There are 40mL of water.

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Scientific Method

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Two parts of measurements 1.Quantity – indicates size or magnitude (how much?) 2.Unit – tells us what is to be measured and compares it to a previously defined size (of what?) Measurements must have both a quantity and a unit to be valid.

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International System of Units Length – meter Length – meter Mass – kilogram Mass – kilogram Temperature – Kelvin Temperature – Kelvin Energy – joule Energy – joule Amount of a substance – mole Amount of a substance – mole Electric current - ampere Electric current - ampere Volume – m 3 Volume – m 3 Density – g/cm 3 Density – g/cm 3 Weight - Newton Weight - Newton

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Commonly Used Prefixes in the Metric System PrefixMeaningExponent mega (M) kilo (k) hecto (h) deka (da) deci (d) 1/ centi (c) 1/ milli (m) 1/ micro (µ) 1/ nano (n) 1/ pico (p) 1/

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Conversion Factors Conversion factors are equalities written in ratio form: Conversion factors are equalities written in ratio form: 1 km = 1000m 1km = 1000 m 1000 m 1 km 1000 m 1 km Choose the format that allows you to cancel the original units and leave the new units. Choose the format that allows you to cancel the original units and leave the new units. Ex. 2.5 km = ________ m You would choose 1000 m You would choose 1000 m km km

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Foldable Can use this to simply move your decimal in order to convert between units Can use this to simply move your decimal in order to convert between units Ex. 1 mg = ? g Ex. 1 mg = ? g

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Conversion Factors Make sure that you have a valid equality before writing your conversion factor. Make sure that you have a valid equality before writing your conversion factor. Which of these equalities are correct? 1 m = 1 x µm 1 m = 1 x 10 6 µm 1 x m = 1µm

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Important Equalities 1 dm 10 cm 1 dm 10 cm 1 dm 10 cm 1 dm 3 = 1000cm 3 1mL = 1cm 3 = 1cc 1dm 3 = 1000 mL = 1L 100 dm 3 = nm 3

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Conversion Practice Problem Problem List in order – largest to smallest a.1 dm 3 b.1 µL c.1 mL d.1 L e.1 cL f.1 dL

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Largest to smallest A. dm 3 D. 1 L F. dL E. cL C. mL B. μL

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Derived Units Derived units are formed from a combination of other units. Derived units are formed from a combination of other units. Examples include: Examples include: m/s & km/hr (speed), cm 3 & dm 3 (volume), J/g·°C (specific heat), g/mol (molar mass), g/cm 3 & kg/m 3 (density)

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Density Density is the ratio between the mass and volume of an object. Density is the ratio between the mass and volume of an object. Density = Mass or D = m Density = Mass or D = m Volume V Volume V Density is an intensive physical property. Density is an intensive physical property.

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Density (Math Triangle) D = M / V D = M / V M = D X V M = D X V V = M / D V = M / D

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Density Problems A student finds a shiny piece of metal that she thinks is aluminum. She determined that the metal has a volume of 245 cm 3 and a mass of 612 g. Calculate the density. Is the metal aluminum? The density of silver at 20ºC is 10.5 g/cm 3. What is the volume of a 68 g bar of silver?

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Density Problems Continued A weather balloon is inflated to a volume of 2.2 x 10 3 L with 37.4 g of helium. What is the density of helium, in grams per liter. A weather balloon is inflated to a volume of 2.2 x 10 3 L with 37.4 g of helium. What is the density of helium, in grams per liter. A plastic ball with a volume of 19.7 cm 3 has a mass of 15.8 g. What is its density? Would the ball sink or float in a container of water? A plastic ball with a volume of 19.7 cm 3 has a mass of 15.8 g. What is its density? Would the ball sink or float in a container of water?

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Specific Gravity Specific Gravity = Density substance (g/cm 3 ) Specific Gravity = Density substance (g/cm 3 ) Density water (g/cm 3 ) Density water (g/cm 3 )

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Making Measurements

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Review Scientific Notation rule: move decimal to a number between ,000 = 600,000 = = 2.3 X = 5.5 X 10 6 =

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Precision and Accuracy Accuracy refers to the agreement of a particular value with the true value. Accuracy refers to the agreement of a particular value with the true value. (how close) (how close) Precision refers to the degree of agreement among several elements of the same quantity. (how repeatable) Precision refers to the degree of agreement among several elements of the same quantity. (how repeatable)

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Target (a) shows neither accuracy or precision. Target (a) shows neither accuracy or precision. Target (b) shows precision, but not accuracy. Target (b) shows precision, but not accuracy. Target (c) shows both accuracy and precision. Target (c) shows both accuracy and precision.

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Uncertainty in Measurement A digit that must be estimated is called uncertain. A digit that must be estimated is called uncertain. The last digit in a measurement always shows uncertainty. The last digit in a measurement always shows uncertainty.

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Significant Digits Significant Digits show the degree of certainty in a measurement. Significant Digits show the degree of certainty in a measurement. Not all digits in a number show certainty, therefore, all digits are not significant. Not all digits in a number show certainty, therefore, all digits are not significant.

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Counting Significant Digits Rule 1: Nonzero integers always count as significant digits. Nonzero integers always count as significant digits has 4 sig digs 3456 has 4 sig digs

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Counting Significant Digits Rule 2: Leading zeros do not count as significant figures. Leading zeros do not count as significant figures has 3 sig figs has 3 sig figs

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Counting Significant Digits Rule 3: Captive zeros always count as significant figures. Captive zeros always count as significant figures has 4 sig digs has 4 sig digs

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Counting Significant Digits Rule 4: Trailing zeros are significant only if the number contains a decimal point. Trailing zeros are significant only if the number contains a decimal point has 4 sig figs has 4 sig figs

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Counting Significant Digits Exact numbers have an infinite number of significant figures. Exact numbers have an infinite number of significant figures. Exact numbers include counting numbers and conversion factors. Exact numbers include counting numbers and conversion factors. Examples: Examples: 12 students 12 students 1m = 100 cm 1m = 100 cm

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Practice Problems Determine the number of significant figures. Determine the number of significant figures. a. 12 kilometers b m 2 c. 507 thumbtacks d m d m e m f m 3. g x 10 3 cm h x atoms

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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. Multiplication and Division: # sig figs in the result equals the number in the least precise measurement used in the calculation cm 2.0 cm = cm cm 2.0 cm = cm 2 13 (2 sig figs) 13 (2 sig figs)

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Multiplication and Division Your answer can only have the least number of significant figures in your data. Your answer can only have the least number of significant figures in your data.a. 2.0 mL x 3.00 mL x 3.00 mLb m = 8432 m = 12.5 m 12.5 m

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Rules for Significant Figures in Mathematical Operations Addition and Subtraction: # sig figs in the result equals the number of decimal places in the least precise measurement. Addition and Subtraction: # sig figs in the result equals the number of decimal places in the least precise measurement. 6.8 cm cm cm = cm 6.8 cm cm cm = cm 22.5 cm (1 digit after decimal - 3 sig figs) 22.5 cm (1 digit after decimal - 3 sig figs)

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Addition and Subtraction Count the decimal places. You can only have in your answer the least number of decimal places that is seen in your data

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Rounding Rules If the digit following the last digit to be retained is: Then the last digit should: Example (rounded to 3 sig digs) greater than 5be increased by g to 38.7 g less than 5stay the same12.51 m to 12.5 m 5, followed by nonzero digit(s) be increased by cm to 4.89 cm 5, not followed by nonzero digit(s), and preceded by an odd digit be increased by kg to 2.98 kg (because 7 is odd) 5, not followed by nonzero digit(s), and the preceding significant digit is even Stay the same2.985 kg to 2.98 kg (because 8 is even)

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Measurement Tips

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Measurement Tools Distance= Meter Sticks & Metric Tapes Volume= Graduated Cylinder Time= Stopwatch Mass= Balance Weight = Spring Scale

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Mass vs. Weight Mass is the amount of matter in an object; weight is the effect of gravity on a mass. Mass is the amount of matter in an object; weight is the effect of gravity on a mass. Mass is measured on a balance; weight is measured with a scale. Mass is measured on a balance; weight is measured with a scale. Mass remains constant at all locations; weight varies with change in gravitational pull. Mass remains constant at all locations; weight varies with change in gravitational pull.

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Volume 1. Never measure in a beaker. They are for estimation only! 2.Place the graduated cylinder on a level surface and read the bottom of the meniscus. 3.Check the scale of the graduated cylinder. Different scales for different sizes! 4.Use displacement to find the volume of irregular solids.

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1. Make sure the balance is on a level surface. Mass 2.Use the same balance in the same place for all parts of a procedure. 3. DO NOT MOVE A BALANCE ONCE IT IS ZEROED!

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Length Rulers & meter sticks wear on the ends – start at a point other than zero. Rulers & meter sticks wear on the ends – start at a point other than zero. Choose the unit most reasonable for the item you are measuring – make sure you convert your number accordingly. Choose the unit most reasonable for the item you are measuring – make sure you convert your number accordingly.

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Symbols Δ Delta means change in Δ Delta means change in Σ Sigma means sum of Σ Sigma means sum of

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Graphing Relationships Direct Relationship-Variables do the same Direct Relationship-Variables do the same Straight Line Straight Line Inverse (Indirect) Relationship-Variables do the opposite Inverse (Indirect) Relationship-Variables do the opposite Parabola Parabola

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Models Why do scientists use models in their research??? Why do scientists use models in their research???

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