Chapter 2: Scientific Measurements Chemistry: The Molecular Nature of Matter, 6E Brady/Jespersen/Hyslop

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E 2 Properties  Characteristics used to classify matter Physical properties  Can be observed without changing chemical makeup of substance Ex. Gold metal is yellow in color  Sometimes observing physical property causes physical change in substance Ex. Melting point of water is 0 °C  Measuring melting temperature at which solid turns to liquid

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E States of Matter Solids:  Fixed shape & volume  Particles are close together  Have restricted motion Liquids:  Fixed volume, but take container shape  Particles are close together  Are able to flow Gases:  Expand to fill entire container  Particles separated by lots of space Ex. Ice, water, steam 3

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E States of Matter Physical Change  Change from 1 state to another Physical States  Important in chemical equations Ex. 2C 4 H 10 (g) + 13O 2 (g)  8CO 2 (g) + 10H 2 O(g)  Indicate after each substance with abbreviation in parentheses  Solids = (s)  Liquids = (ℓ)  Gases = (g)  Aqueous solutions = (aq) 4

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E 5 Chemical Properties  Chemical change or reaction that substance undergoes  Chemicals interact to form entirely different substances with different chemical & physical properties  Describes behavior of matter that leads to formation of new substance  “Reactivity" of substance Ex. Iron rusting  Iron interacts with oxygen to form new substance

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E 6 Learning Check: Chemical or Physical Property? ChemicalPhysical X X X X Magnesium metal is grey Magnesium metal tarnishes in air Magnesium metal melts at 922 K Magnesium reacts violently with hydrochloric acid

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E 7 Intensive vs. Extensive Properties Intensive properties  Independent of sample size  Used to identify substances Ex. Color Density Boiling point Melting point Chemical reactivity Extensive properties  Depend on sample size Ex. volume & mass

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Your Turn! Which of the following is an extensive property? A. Density B. Melting point C. Color D. Temperature E. Mass 8

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Measurements Include Units!! 1.Measurements involve comparison  Always measure relative to reference Ex. Foot, meter, kilogram  Measurement = number + unit Ex. Distance between 2 points = 25  What unit? inches, feet, yards, miles  Meaningless without units!!! 2.Measurements are inexact  Measuring involves estimation  Always have uncertainty  The observer & instrument have inherent physical limitations 9

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E International System of Units (SI)  Standard system of units used in scientific & engineering measurements  Metric  7 Base Units 10

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E SI Units  Focus on 1 st six in this book  All physical quantities will have units derived from these 7 SI base units Ex. Area  Derived from SI units based on definition of area  length × width = area  meter × meter = area m × m = m 2  SI unit for area = square meters = m 2 Note: Units undergo same kinds of mathematical operations that numbers do! 11

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Learning Check  What is the SI unit for velocity?  What is the SI unit for volume of a cube? Volume (V) = length × width × height V = meter × meter × meter V = m 3 12

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Your Turn! The SI unit of length is the A.millimeter B.meter C.yard D.centimeter E.foot 13

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Table 2.2 Some Non-SI Metric Units Commonly Used in Chemistry 14

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Decimal Multipliers 15

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Using Decimal Multipliers  Use prefixes on SI base units when number is too large or too small for convenient usage  Only commonly used are listed here  For more complete list see Table 2.4 in textbook  Numerical values of multipliers can be interchanged with prefixes Ex. 1 mL = 10 –3 L  1 km = 1000 m  1 ng = 10 –9 g  1,130,000,000 s = 1.13 × 10 9 s = 1.13 Gs 16

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Laboratory Measurements 1.Length  SI Unit is meter (m)  Commonly use  Centimeter (cm)  1 cm = 10 – 2 m = 0.01 m  Millimeter (mm)  1 mm = 10 – 3 m = m 17

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E 2. Volume (V)  Dimensions of (length) 3  SI unit for Volume = m 3  Most laboratory measurements use V in liters (L)  1 L = 1 dm 3 (exactly)  What is a mL?  1 mL = 1 cm 3 18

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E 3. Mass  SI unit is kilogram (kg)  Frequently use grams (g) in laboratory as more realistic size  1 kg = 1000 g 1 g = kg = g 19

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E 4. Temperature  Measured with thermometer  3 common scales A.Fahrenheit scale  Common in US  Water freezes at 32 °F and boils at 212 °F  180 degree units between melting & boiling points of water 20

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E 4. Temperature B.Celsius scale  Rest of world (aside from U.S.) uses  Most common for use in science  Water freezes at 0 °C  Water boils at 100 °C  100 degree units between melting & boiling points of water 21

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E 4. Temperature C. Kelvin scale  SI unit of temperature is kelvin (K)  Note: No degree symbol in front of K  Water freezes at K & boils at K  100 degree units between melting & boiling points  Only difference between Kelvin & Celsius scale is zero point Absolute Zero  Zero point on Kelvin scale  Corresponds to nature’s lowest possible temperature 22

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Temperature Conversions  How to convert between °F and °C? Ex. 100 °C = ? °F t F = 212 °F 23

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Temperature Conversions  Common laboratory thermometers are marked in Celsius scale  Must convert to Kelvin scale  Amounts to adding to Celsius temperature Ex. What is the Kelvin temperature of a solution at 25 °C? 24 = 298 K

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Learning Check: T Conversions 1. Convert 100. °F to the Celsius scale. 2. Convert 100. °F to the Kelvin scale.  We already have in °C so… 25 = 38 °C T K = 311 K

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Learning Check: T Conversions 3. Convert 77 K to the Celsius scale. 4. Convert 77 K to the Fahrenheit scale.  We already have in °C so 26 = – 196 °C = – 321 °F

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Your Turn! In a recent accident some drums of uranium hexafluoride were lost in the English Channel. The melting point of uranium hexafluouride is °C. What is the melting point of uranium hexafluoride on the Fahrenheit scale? A °F B °F C °F D °F E °F 27

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Significant Figures  Scientific convention:  All digits in measurement up to & including 1 st estimated digit are significant.  Number of certain digits plus 1 st uncertain digit  Digits in measurement from 1 st non-zero number on left to 1 st estimated digit on right 28

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E 1.All non-zero numbers are significant. Ex has 4 sig. figs. 2.Zeros between non-zero numbers are significant. Ex. 20,089 or × 10 4 has 5 sig. figs 3.Trailing zeros always count as significant if number has decimal point Ex or 5.00 × 10 2 has 3 sig. figs 29 Rules for Significant Figures

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E 4.Final zeros on number without decimal point are NOT significant Ex. 104,956,000 or × 10 8 has 6 sig. figs. 5.Final zeros to right of decimal point are significant Ex has 3 sig. figs. 6. Leading zeros, to left of 1 st nonzero digit, are never counted as significant Ex or1.2 × 10 –4 has 2 sig. figs. 30 Rules for Significant Figures

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Learning Check How many significant figures does each of the following numbers have? scientific notation # of Sig. Figs , × × 10 – × ×

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Rounding to Correct Digit 1.If digit to be dropped is greater than 5, last remaining digit is rounded up. Ex is rounded up to If number to be dropped is less than 5, last remaining digit stays the same. Ex is rounded to If number to be dropped is 5, then if digit to left of 5 is a.Even, it remains the same. Ex is rounded to 6.6 b.Odd, it rounds up Ex is rounded to

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Learning Check Round each of the following to 3 significant figures. Use scientific notation where needed or 3.75 × × or 1.33 × × 10 –4 7.66

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Significant Figures in Calculations Multiplication and Division  Number of significant figures in answer = number of significant figures in least precise measurement Ex × 31.4 × sig. figs. × 3 sig. figs. × 5 sig. figs = 3 sig. figs. Ex ÷ sig. figs. ÷ 1 sig. fig. = 1 sig. fig. 34 = 5620 = 5.62×10 3 = 700 = 7×10 2

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Your Turn! Give the value of the following calculation to the correct number of significant figures. A B C D. 1.2 E. 1 35

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Significant Figures in Calculations Addition and Subtraction  Answer has same number of decimal places as quantity with fewest number of decimal places. Ex decimal places 1 decimal place 3 decimal places 1 decimal place 397 – decimal places 2 decimal places 0 decimal place

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Your Turn! When the expression, – is evaluated, the result should be expressed as: A B C D E

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Exact Numbers  Number that come from definitions  12 in. = 1 ft  60 s = 1 min  Numbers that come from direct count  Number of people in small room  Have no uncertainty  Assume they have infinite number of significant figures.  Do not affect number of significant figures in multiplication or division 38

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Learning Check For each calculation, give the answer to the correct number of significant figures g g g = °C – °C = m × 4.52 m = g ÷ mL = g or 1.13 × 10 1 g °C or 4 × 10 –3 °C 1.48 × 10 3 m g/mL or g/mL

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Learning Check For the following calculation, give the answer to the correct number of significant figures = 2 × 10 –4 m/s 2 = 0.87 cm 3 /s

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Your Turn! For the following calculation, give the answer to the correct number of significant figures. A. 179 cm 2 B cm C cm D. 151 cm E cm 2 41

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Dimensional Analysis  Factor-Label Method  Not all calculations use specific equation  Use units (dimensions) to analyze problem Conversion Factor  Fraction formed from valid equality or equivalence between units  Used to switch from one system of measurement & units to another 42 Given Quantity Desired Quantity Conversion Factor ×=

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Using Dimensional Analysis Ex. Convert m to mm.  Relationship is1 mm = 1 × 10 –3 m  Can make 2 conversion factors  Since going from m to mm use one on left. 43 = 173 cm

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Learning Check Ex. Convert 3.5 m 3 to cm 3.  Start with basic equality 1 cm = 0.01 m  Now cube both sides  Units & numbers  (1 cm) 3 = (0.01 m) 3  1 cm 3 = 1 × 10 –6 m 3  Can make 2 conversion factors 44 or 3.5 × 10 6 Cm 3

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Non-metric to Metric Units Convert speed of light from 3.00×10 8 m/s to mi/hr  Use dimensional analysis  1 min = 60 s60 min = 1 hr  1 km = 1000 m1 mi = km × m/hr

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Density  Ratio of object’s mass to its volume  Intensive property (size independent)  Determined by taking ratio of 2 extensive properties (size dependent)  Frequently ratio of 2 size dependent properties leads to size independent property  Sample size cancels  Units  g/mL or g/cm 3 46

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Learning Check  A student weighs a piece of gold that has a volume of cm 3 of gold. She finds the mass to be 212 g. What is the density of gold? g/cm 3

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Density  Most substances expand slightly when heated  Same mass  Larger volume  Less dense  Density  slightly as T   Liquids & Solids  Change is very small  Can ignore except in very precise calculations  Density useful to transfer between mass & volume of substance 48

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Learning Check 1. Glass has a density of 2.2 g/cm 3. What is the volume occupied by 22 g of glass? 2. What is the mass of 400 cm 3 of glass? g/cm g

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Specific Gravity  Ratio of density of substance to density of water  Unitless  Way to avoid having to tabulate densities in all sorts of different units 50

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Learning Check Concentrated sulfuric acid is sold in bottles with a label that states that the specific gravity at 25 °C is The density of water at 25 °C is g cm –3. How many cubic centimeters of sulfuric acid will weigh 5.55 kilograms? Analysis: 5.55 kg sulfuric acid = ? cm 3 sulfuric acid Solution: density sulfuric acid = specific gravity × density water d sulfuric acid = 1.84 × g/cm 3 = × 10 3 cm3

Brady/Jespersen/Hyslop Chemistry: The Molecular Nature of Matter, 6E Your Turn! Liquid hydrogen has a specific gravity of 7.08 × 10 –2. If the density of water is 1.05 g/cm 3 at the same temperature, what is the mass of hydrogen in a tank having a volume of 36.9 m 3 ? A × 10 –2 g B g C. 274 g D × 10 6 g E × 10 6 g 52 = 7.43 × 10 –2 g/cm 3