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**Scientific Measurement**

Chapter 3 Scientific Measurement

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**Measurement A quantity that has both a number and a unit.**

Units used in sciences are those of the International System of Measurements (SI).

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**Sometimes in chemistry numbers can be very large or very small**

1 gram of hydrogen = 602,000,000,000,000,000,000,000 atoms Mass of an atom of gold = gram

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Scientific Notation A given number is written as the product of two numbers: a coefficient and 10 raised to a power. M x 10n Example: 602,000,000,000,000,000,000,000 will be written as 6.02 x 1023.

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**Accuracy, Precision, and Error**

Accuracy is a measure of how close a measurement comes to the actual or true value Precision is a measure of how close a series of measurements are to one another

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Determining Error Table T % error = accepted value −experimental value accepted value x 100% A student estimated the volume of a liquid in a beaker as 200mL. When she poured the liquid into a graduated cylinder she measured the volume as 208mL. Calculate the % error.

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**Significant Figures in Measurement**

Include all of the digits that are known, plus the last digit that is estimated.

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**The Rules of Significant Figures**

Every nonzero digit is significant, numbers 1-9. Example: 24.7 meters (3 sig. figs.) Zeros between nonzero digits are significant. Example: meters (4 sig. figs.) Zeros appearing to the left of nonzero digits are not significant. They are only place holders. Example: (2 sig. figs) 7.1 x 10-3 (2 sig. figs.)

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**Zeros at the end of a number and to the right of a decimal point are significant.**

Example: meters (4 sig. figs.) 1.010 meters (4 sig. figs) Zeros at the right end of a measurement that lie to the left of an understood decimal point are not significant. Example: 300 meters (1 sig. figs.) 27,210 meters (4 sig. figs.)

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Practice Problems How many significant figures are in each measurement? 123 meters = x 104 m = m = 40,506 mm = 98, 000 m = 3 5 4 5 2

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**Practice Problems Count the significant figures in each length**

meters 8765 meters meters meters 4 4 2 5

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Practice Problems How many significant figures are in each measurement? 143 grams 0.074 meters 8.750 x 10-2 grams 1.072 meters 3 2 4 4

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**Significant Figures in Calculations**

A calculated answer cannot be more precise than the least precise measurement from which it was calculated.

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Sample Problems Round off each measurement to the number of significant figures shown in parentheses. meters (four) meter (two) 8792 meters (two) 314.7 0.0018 8800

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**Practice Problems Round each measurement to three significant figures.**

meters x 108 meters meter 9009 meters x 10-3 meter meters 87.1 4.36 x 108 0.0155 9010 1.78 x 10-3 630.

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**Addition and Subtraction**

The answer to an addition or subtraction calculation should be rounded to the same number of decimal places (not digits) as the measurement with the least number of decimal places

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Sample Problem Calculate the sum of the three measurements. Give the answer to the correct number of significant figures. 12.52 meters meters meters 369.76

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Practice Problems Perform each operation. Express your answers to the correct number of significant figures. 61.2 meters meters meters 9.44 meters – 2.11 meters 1.36 meters meters 34.61 meters – 17.3 meters 79.2 7.33 11.53 17.3

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**Multiplication and Division**

You need to round the answer to the same number of significant figures as the measurement with the least number of significant figures.

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Sample Problem Perform the following operations. Give the answers to the correct number of significant figures. 7.55 meters x 0.34 meter 2.10 meters x 0.70 meter meters / 8.4 meters 2.6 m2 1.5 m2 0.29 m

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Practice Problems Solve each problem. Give your answers to the correct number of significant figures. 8.3 meters x 2.22 meters 8432 meters / 12.5 meters Calculate the volume of a warehouse that has inside dimensions of 22.4 meters by 11.3 meters by 5.2 meters (volume = l x w x h) 18 m2 675 m 1300 m3

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Section Assessment A technician experimentally determined the boiling point of octane to be 124.1C. The actual boiling point of octane is 125.7C. Calculate the percent error. 1.27 %

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Section Assessment Determine the number of significant figures in each of the following. meter 10,800 meters 5.00 cubic meters 5 3 3

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**The International System of Units (SI)**

Table D Length Meters (m)

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Volume Liter (L) cm3 Mass Kilograms (Kg)

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**Temperature A measure of how hot or cold an object is.**

Heat moves from the object at the higher temperature to the object at the lower temperature

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Celsius (C) Freezing point of water (0C) Boiling point of water (100C) Kelvin (K) Freezing point of water (273 K) Boiling point of water (373 K) Absolute Zero (0K), the coldest possible temperature ( ? Celsius) K = C + 273 C = K -273

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Figure: 01-18

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Sample Problems Liquid nitrogen boils at 77.2 K. What is this temperature in degrees Celsius? Normal human body temperature is 37 C. What is that temperature in Kelvins? 310 K K

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**The element silver melts at 960. 8 C and boils at 2212 C**

The element silver melts at C and boils at 2212 C. Express these temperatures in Kelvins. Melting Point: 1,233.8 K Boiling Point: 2485 K

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**Section Assessment 882 cm3 443 K**

What is the volume of a paperback book, 21cm tall, 12cm wide, and 3.5cm thick? Surgical instruments may be sterilized by heating at 170 C for 1.5 hr. Convert 170 C to Kelvins. 882 cm3 443 K

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Conversion Problems A conversion factor is a ratio of equivalent measurements. When a measurement is multiplied by a conversion factor, the numerical value is generally changed, but the actual size of the quantity measured remains the same.

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Dimensional analysis is a way to analyze and solve problems using the units, or dimensions, of the measurements

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Figure: TB01-T05

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Sample Problems How many seconds are in a workday that lasts exactly 8 hours? How many minutes are there in exactly one week? How many seconds are in exactly a 40 hour work week? 28800 seconds 10,080 minutes 144,000 seconds

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**Converting Between Units**

Problems in which a measurement with one unit is converted to an equivalent measurement with another unit are easily solved using dimensional analysis

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**Sample Exercise Convert the following 0.044 km to meters**

4.6 mg to grams 0.107 g to centigrams 7.38 g to kilograms 6.7 s to milliseconds 94.5 g to micrograms 44 m g 10.7 cg kg 6700 ms μg

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**Section Assessment Convert the following.**

Light travels at a speed of 3.00 x 1010 cm/sec. What is the speed of light in kilometers/hour?

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Density (Table T) Density is an intensive property that depends only on the composition of a substance, not on the size of the sample. The density of a substance generally decreases as its temperature increases (inverse relationship)

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**Practice Problems 8.9 g/mL**

A copper (Cu) penny has a mass of 3.1g and a volume of 0.35 mL. What is the density of copper? 8.9 g/mL

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A student finds a shiny piece of metal that she thinks is aluminum (Al). In the lab, she determines that the metal has a volume of 245 cm3 and a mass of 612 g. Calculate the density. Is the metal aluminum? 2.45 g/cm3

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Practice Problems A bar of silver (Ag) has a mass of 68.0 g and a volume 6.48 cm3. What is the density of silver? What is the density of silver (Ag) if a g sample has a volume of 2.62 mL? 10.5 g/cm3 10.5 g/cm3

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**A sample of ethylene glycol has a volume of 45. 8 mL**

A sample of ethylene glycol has a volume of 45.8 mL. What is the mass of this sample if the density of ethylene glycol is 1.11g/mL? 50.8 g

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Sample Problem What is the volume of a pure silver coin that has a mass of 14 g. 1.33 cm3

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Section Assessment What is the volume in cubic centimeters, of a sample of cough syrup that has a mass of 50.0 g? The density of cough syrup is g/ cm3. 52.6 cm3

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