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chapter 1 CHEM 205 Tutorial 0 http://www.karentimberlake.com/chemodul.htm

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Units of measurement

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Measurement Measurement You are making a measurement when you Check you weight Read your watch Take your temperature Weigh an apple What kinds of measurements did you make today?

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Some Tools for Measurement How do you measure…. Temperature? Time? Volume? Weight?

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Measurement in Science In Science we do experiments measure quantities use numbers to report measurements

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Units in the Metric System (S.I.) length meter m volumeliter L mass gram g temperatureCelsius °C

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Stating a Measurement In every measurement there is a NUMBER followed by a UNIT from measuring device The patient’s temperature is 102°F. The sack holds 5 lbs of potatoes. It is 8 miles from your house to school. The bottle holds 2 L of orange soda

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Significant Figures

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Reading a measure First digit (known)= 2 2.?? cm Second digit (known)= 0.7 2.7? cm Third digit (estimated) between 0.05- 0.07 Length reported=2.74 cm or2.75 cm or2.73 cm

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Known, significant, estimated digits 2.74 cm Known (100% certain) Estimated (uncertain) Significant!

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l 5.... I.... I 6....I.... I 7.. cm 1) 6.0 cm 2) 6.06 cm 3) 6.60 cm What is the length of the line?

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Exact Numbers Obtained when you count objects 2 soccer balls 1 watch 3 pizzas Obtained from a defined relationship 1 foot = 12 inches 1 meters = 100 cm Not obtained with measuring tools

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A._M_Gold melts at 1064°C B._E_1 yard = 3 feet C._M_A red blood cell with diameter 6 x 10 -4 cm D._E_There were 6 hats on the shelf E._M_A can of soda contains 355 mL of soda Classify each of the following as an exact (E) or a measured (M) number. A.___Gold melts at 1064°C B.___1 yard = 3 feet C.___A red blood cell with diameter 6 x 10 -4 cm D.___There were 6 hats on the shelf E.___A can of soda contains 355 mL of soda

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Significant Figures in Calculations

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Number of Significant Figures 38.15 cm 0.008 ft 25000 in 0.48600 gal 4 1 2 5 Counting Significant Figures

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Significant Numbers in Calculations A calculated answer cannot be more precise than the measuring tool. Significant figures are needed for final answers from 1) adding or subtracting 2) multiplying or dividing

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Adding and Subtracting The answer has the same number of decimal places as the measurement with the fewest decimal places. 25.2 ONE decimal place + 1.34 TWO decimal places 26.54 answer 26.5 ONE decimal place

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In each calculation, round the answer to the correct number of significant figures. A. 235.05 + 19.6 + 2.1 = 1) 256.75 2) 256.83) 257 B. 58.925 - 18.2= 1) 40.725 2) 40.733) 40.7

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Multiplying and Dividing Round (or add zeros) to the calculated answer until you have the same number of significant figures as the measurement with the fewest significant figures.

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A. 2.19 X 4.2 = 1) 9 2) 9.2 3) 9.198 B. 4.311 ÷ 0.07 = 1) 61.58 2) 62 3) 60 C. 2.54 X 0.0028 = 0.0105 X 0.060 1) 11.32) 11 3) 0.041 In each calculation, round the answer to the correct number of significant figures.

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Prefixes and Equalities

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Metric Prefixes Increase or decrease basic unit by 10 Form new units larger or smaller than the basic units 0.00356 = 3.56 x 10 -3 123 000 000 000 000 = 123 x 10 12

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PrefixSymbolValueExponential gigaG1,000,000,00010 9 megaM1,000,00010 6 kilok1,00010 3 hectoh10010 2 decada1010 1 no prefix means:110 0 decid0.110 -1 centic0.0110 - 2 millim0.00110 -3 microm0.00000110 -6 nanon0.00000000110 -9

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A. 1 kg = ____ g 1) 10 g2) 100 g 3) 1000 g B. 1 mm = ____ m 1) 0.001 m2) 0.01 m 3) 0.1 m Give the value of the following units:

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Equalities State the same measurement in two different units length 10.0 in. 25.4 cm

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Conversion Factors Express an equality between two different units Example: 1 in = 2.54 cm Factors: 1 in and 2.54 cm 2.54 cm 1 in 3 in → ? cm 3 in x= 7.62 cm 8

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Initial unit = pintsFinal unit = Blood has a density of 0.05 g/mL. If a person lost 0.30 pints of blood at 18°C, how many ounces of blood would that be? oz 1 US pint = 16 US fluid ounces

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How many seconds are in 14 days? 14 day x 1 day x 60 min x 60 s 24 h 1 h 1 min 14 day x 24 h x 60 min x 60 s 1 day 1 h 1 min = 1.2 x 10 5 s

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READ problem IDENTIFY data Write down a unit plan from the INITIAL UNIT to the DESIRED UNIT Select CONVERSION factors Change initial unit to desired unit CANCEL units and check Do math on CALCULATOR (is the result logical?) Give an answer using SIGNIFICANT FIGURES Steps to solve a problem

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Measuring Temperature

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Kelvin Scale 0 K is the lowest temperature 0 K = - 273°C K °C K = °C + 273 37°C to K? K= °C + 273 = = 37°C + 273 = = 310 K °C = K - 273 298K to °C ? °C = K - 273 = = 298 - 273 = = 25 °C

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Density

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Density Density compares the mass of an object to its volume Note: 1 mL = 1 cm 3

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1) 0.2 g/ cm 3 2) 6 g/cm 3 3) 252 g/cm 3 25 mL 33 mL What is the density (g/cm 3 ) of 48 g of a metal if the metal raises the level of water in a graduated cylinder from 25 mL to 33 mL?

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Volume (mL) of water displaced = 33 mL - 25 mL= 8 mL Volume of metal (cm 3 ) = 8 mL x 1 cm 3 = 8 cm 3 1 mL Density of metal = mass = 48 g = 6 g/cm 3 volume 8 cm 3 Solution: 6 g/cm 3 (#2) What is the density (g/cm 3 ) of 48 g of a metal if the metal raises the level of water in a graduated cylinder from 25 mL to 33 mL?

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W V K Which diagram represents the liquid layers in the cylinder? (K) Karo syrup (1.4 g/mL) (V) vegetable oil (0.91 g/mL) (W) water (1.0 g/mL) W V K W V K 123

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Density as Conversion Factor A substance has a density of 3.8 g/mL. Density = 3.8 g/mL Equality 3.8 g = 1 mL = 1 cm 3 Conversion factors:

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1) 0.614 kg 2) 614 kg 3) 1.25 kg The density of octane, a component of gasoline, is 0.702 g/mL. What is the mass, in kg, of 875 mL of octane?

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Unit plan: mL g kg Equalities: 1 mL = 0.702 g and 1 kg = 1000 g Calculation: 875 mL x 0.702 g x 1 kg = 0.614 kg 1 mL 1000 g Solution: 0.614 kg (#1) The density of octane, a component of gasoline, is 0.702 g/mL. What is the mass, in kg, of 875 mL of octane?

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