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Chemistry I

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English - Metric Conversions. Length. 2.54 cm = 1 inch. 1 mi = 5280 ft. 1 mi = 1.609 km ... English-Metric Conversions. Problem Solving ... – PowerPoint PPT presentation

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Title: Chemistry I


1
Chapter 2
  • Chemistry I
  • Ms Appleby

2
Units and Measurements
  • International System of Units, SI
  • The metric system
  • Standard in the scientific community
  • Measurements are based on units of 10

3
Base Unit and SI Prefixes
  • Prefix Symbol Power of 10 Numerical
    value
  • Giga (G-) 109 1 billion
  • Mega (M-) 106 1 million
  • Kilo (k-) 103 1 thousand
  • Hecto (h-) 102 1 hundred
  • Deka (da-) 10 1 ten
  • Deci (d-) 10-1 1 tenth
  • Centi (c-) 10-2 1 hundredth
  • Milli (m-) 10-3 1 thousandth
  • Micro (µ-) 10-6 1 millionth
  • Nano (n-) 10-9 1 billionth
  • Pico (p-) 10-12 1 trillionth

4
Time
  • SI unit is the second (s)
  • The standard to define a second is the frequency
    of radiation given off by a cesium-133 atom
  • Cesium based clocks are highly accurate
  • Although a second seems like a short period of
    time, in chemistry many reactions occur in a
    fraction of a second

5
Length
  • The basic SI unit is the meter (m)
  • A meter stick is divided into 100 divisions
  • Each division is a centimeter
  • A centimeter is divided into 10 divisions
  • Each division is a millimeter
  • One meter is the distance light travels in a
    vacuum in 1/299,792,458 of a second

6
Mass
  • Mass is the quantity of matter an object contains
  • Mass is not weight, weight is a force
  • The SI unit of mass is the kilogram (kg)

7
Temperature
  • The degree of hotness or coldness of an object
  • Nearly all substances expand with an increase in
    temperature
  • Likewise they will contract with a decrease in
    temperature
  • An important exception is water

8
Fahrenheit
  • Used in the US to measure temperature
  • Scale was devised in 1724 by a German scientist
  • On this scale water freezes at 32F
  • On this scale water boils at 212F

9
Celsius
  • Freezing point of water is 0C
  • Boiling point of water is 100C
  • To convert from F to C subtract 32 and multiply
    by 5/9

10
Kelvin
  • The freezing point of water is 273K
  • The boiling point of water is 373K
  • 0 Kelvin, or absolute zero equals
  • -273C
  • To convert from C to Kelvin add 273
  • http//www.absolutezerocampaign.org/

11
Derived Unit
  • Unit that is a combination of base units
  • Speed m/s
  • Volume cm3
  • Density g/cm3

12
Volume
  • The space occupied by an object
  • The volume of an object with a regular shape is
    determined by multiplying the length x width x
    height (l x w x h) and is measured in cm3
  • The volume of an irregularly shaped solid, or a
    liquid is expressed in liters (L)
  • 1mL 1 cm3

13
Density
  • A physical property of matter
  • Defined as unit of mass per unit of volume
  • Density mass/volume
  • For solids the units are g/cm3
  • For liquids the units are g/mL
  • Density can be used to identify an unknown
    element

14
English - Metric Conversions
  • Length
  • 2.54 cm 1 inch
  • 1 mi 5280 ft
  • 1 mi 1.609 km
  • Temperature Conversions
  • 0C (0F - 32) x 5/9
  • 0F (9/5 x 0C) 32
  • K 0C 273

15
English-Metric Conversions
  • Mass
  • 454 g 1 lb
  • 1 lb 0.453 kg

16
English-Metric Conversions
  • Volume
  • 1 L 1.057 qt
  • 1 oz 28.350 g
  • 1 gal 3.785 L
  • 8 oz 1 cup
  • 2 cups 1 pint
  • 2 pints 1 quart
  • 4 quarts 1 gallon

17
Problem Solving
  • Solving a problem is like taking a trip to a new
    place
  • It takes planning and a knowledge of what your
    starting point is and where you want to end up

18
Techniques of Problem Solving
  • Identify the unknown
  • Identify What is Known or Given
  • Plan a Solution
  • Do the calculations
  • Finish Up
  • Check your work!

19
Identify the Unknown
  • Know what the problem is asking
  • Read the problem carefully
  • What will the unit of the answer be

20
Identify What is Known
  • This usually includes a measurement
  • Learn to recognize which information is extra

21
Plan a Solution
  • Sketching a picture of the
    problem may help you see
    a relationship between the known
    and the unknown
  • Break down a complex problem into simpler
    problems
  • You may need to look up a conversion or a formula

22
Do The Calculations
  • This may involve solving an equation
  • Substituting in known quantities
  • Doing arithmetic
  • You may need to convert a measurement form one
    form to another
  • Be sure to use relationships correctly to move
    from the given quantity to the unknown

23
Finish Up
  • The answer should always be expressed to the
    correct number of significant figures
  • When appropriate,
    the number should
    be written in
    scientific notation

24
Check Your Work!
  • Have you found what was asked for
  • Check your math
  • Check your units
  • Does the answer
    make sense
  • Is it reasonable

25
Density Webpage
  • http//www.nyu.edu/pages/mathmol/textbook/density.
    html

26
Scientific Notation and Dimensional Analysis
  • The Hope Diamond contains 460,000,000,000,000,000,
    000,000 atoms of carbon
  • Each carbon atom has a mass of 0.00000000000000000
    000002 g.
  • If you were to use these numbers to calculate the
    mass of the Hope Diamond you would find the
    zeroes get in the way and a calculator is no help

27
Scientific Notation
  • Used to express any number as a number between 1
    and 10 (the coefficient)
  • Multiplied by 10 and raised to a power (the
    exponent)
  • In scientific notation the number of carbon atoms
    in the Hope Diamond 4.6 x 1023
  • The mass of one carbon atom 2 x 10-23

28
Scientific Notation
  • In each case the number 10 raised to an exponent
    replaced the zeroes that preceded or followed the
    nonzero numbers
  • For numbers greater than 1 a positive exponent
    tells you the number of places the decimal must
    be moved to the right when converting to a whole
    number
  • For numbers less than 1 a negative exponent tells
    you the number of places the decimal must be
    moved to the left

29
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30
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31
Scientific Notation Practice Problems
  • Use this site to hone your scientific notation
    skills.
  • http//science.widener.edu/svb/tutorial/scinotcsn7
    .html

32
Multiplication with Exponents
  • When performing multiplication with exponents, do
    the multiplication and add the exponents
  • (2.68 x 10-5) x (4.40 x 10-8)
  • (8.41 x 106) x (5.02 x 1012)
  • (4.6 x 1023) x (2 x 10-23)

33
Division with Exponents
  • When performing division, do the division and
    subtract the exponents
  • (2.95 x 107) (6.28 x 1015)
  • (9.21 x 10-4) (7.60 x 105)
  • (4.6 x 1023) (2 x 10-23)

34
Another Look Multiplication/Division in
Scientific Notation
  • http//www.regentsprep.org/Regents/math/scinot/pag
    e4.htm

35
Addition and subtraction are more complex
  • There are four basic steps
  • Find the number whose exponent is the smallest
    (remember, negative numbers are smaller than
    positive ones, and the "more negative" the
    number, the smaller it is).
  • If the exponents of the numbers are not the same,
    change the number with the smaller exponent. Do
    this by moving the decimal point of the
    coefficient of that number to the left, and
    adding one to the exponent of that number, until
    the two exponents are equal.

36
Addition and Subtraction of Exponents
  • Four Basic Steps, Continued
  • 3. Add or subtract the coefficients of the two
    numbers. The result is the coefficient of the
    result. The exponent is the exponent of the
    number you did not change
  • 4. Put the result in standard form, if necessary

37
Examples
  • (3 x 10-6) - (2 x 10-7)
  • The algebraically smallest exponent is -7, so we
    change the second term to match the first
  • 2 x 10-7 0.2 x 10-6 The exponents are now the
    same
  • (3 x 10-6) - (0.2 x 10-6)
  • (3 - 0.2) x 10-6
  • 2.8 x 10-6

38
Example
  • (9.39 x 105) (8 x 103)
  • (9.39 x 105) (0.08 x 105)
  • (9.39 0.08) x 105
  • 9.47 x 105

39
Addition and Subtraction
  • 3.2 x 103 4.25 x 105
  • 6.2 x 108 7.6 x 106
  • 2.6 x 10-4 1.8 x 10-5
  • 5.0 x 10-1 3.9 x 10-3

40
Equalities
  • Which of these numbers are equal to each other?
  • 5.678 x 10 3     
  • 56.78 x 10 2  
  • 567.8 x 10 1
  • 0.5678 x 10 4    
  • 0.05678 x 10 5 
  • 0.005678 x 10 6

41
Conversion Factors
  • Equality relationships can be written as a
    conversion factor to allow you to change from one
    unit to another
  • 12 inches 1 foot
  • 12 eggs 1 dozen eggs
  • Anything that can be written as an equality can
    be used as a ratio
  • A conversion factor must cancel one unit and
    introduce a new unit

42
Conversions
  • 0.044 km to meters
  • 4.6 mg to grams
  • 8.9 m to decimeters
  • 0.107 g to centigrams
  • 15 cm3 to liters
  • 7.38 g to kilograms
  • 6.7 s to milliseconds
  • 94.5 g to micrograms

43
Conversion problems
  • How many eight packs of water would you need if
    32 people each had two bottles of water?
  • If Noah built his Ark 60 cubits in length, how
    long was the Ark in meters?
  • A cubit is equal to 7 palms, a palm is equal to 4
    fingers, and a finger is equal to 18.75
    millimeters.

44
Conversion Problems
  • Who is taller a man 1.62 m tall or a woman who
    is 56 tall?
  • A 1 kg package of hamburger has a mass closest
    to 8 oz 1 lb 2 lb 10 lb
  • A recipe in metric calls for 250 ml of milk. How
    much milk (in cups) should be used?
  • The Greenland Ice Sheet has an area of 1.7
    million square kilometers (about the size of
    Mexico). How many square miles is this? 1 mile
    1.609 kilometer
  • You are doing 65 mi/hr and you take your eyes off
    the road for just a second. How many feet do
    you travel in this time?

45
Accuracy and Precision
  • Measurements in the lab must be certain
  • When scientist make measurements they evaluate
    the accuracy and precision of the measurements
    they make
  • Accuracy is how close a measured value is to the
    accepted value
  • Precision is how close are series of measurements
    are to each other

46
Accuracy
  • How close a single measurements comes to the
    actual value of that which is being measured
  • In a dart game your closeness
  • to the bulls eye is a test of
  • your accuracy

47
Precision
  • How close several measurements are to the same
    value
  • Precise measurements are reproducible

48
Precision vs Accuracy
  • Precision depends on more than one measurement
  • Individual measurements may be either accurate or
    inaccurate
  • Precision depends on the skill of the person
    taking the measurement
  • Accuracy depends on the quality of the measuring
    device

49
Checking the accuracy of your measurements
  • The accepted value is the true or correct value
  • The experimental value is the measured value
    found in the lab
  • The difference between the two is the
    experimental error
  • Error accepted value-experimental value

50
Percent Error
  • The percent error is the error divided by the
    accepted value expressed as a percentage of the
    accepted value
  • error   your result - accepted value x100
                              accepted value
  • This tells us how accurate we are, or how closely
    our experimental value compares to the known value

51
Calculating Error
  • Example  A student measures the volume of a 2.50
    liter container to be 2.38 liters. What is the
    percent error in the student's measurement?
  • Ans.      error (2.38 liters 2.5 liters) 
    x   100                                   2.50
    liters
  •                          .12 liters     x   
    100                             2.50 liters
  •                           .048     x   100
  •                           4.8 error

52
Significant Figure Rules
  • There are three rules on determining how many
    significant figures are in a number
  • Non-zero digits are always significant.
  • Any zeros between two significant digits are
    significant.
  • A final zero or trailing zeros in the decimal
    portion ONLY are significant.

53
Rule 1 Non-zero digits are always significant.
  • Hopefully, this rule is rather obvious
  • If you measure something and the device you use
    (ruler, thermometer, triple-beam balance, etc.)
    returns a number to you, then you have made a
    measurement decision and that ACT of measuring
    gives significance to that particular numeral (or
    digit) in the overall value you obtain
  • A number like 26.38 would have four significant
    figures and 7.94 would have three

54
Rule 2 Any zeros between two significant digits
are significant.
  • Suppose you had a number like 406
  • By the first rule, the 4 and the 6 are
    significant
  • However, to make a measurement decision on the 4
    (in the hundred's place) and the 6 (in the unit's
    place), you HAD to have made a decision on the
    ten's place
  • The zero is significant because there are zero
    tens

55
Rule 3 A final zero or trailing zeros in the
decimal portion are significant.
  • This rule causes the most difficulty
  • Here are two examples of this rule with the zeros
    this rule affects in boldface
  • 0.00500
  • 0.03040
  • Here are two more examples where the significant
    zeros are in boldface
  • 2.30 x 105
  • 4.500 x 1012

56
Zeros that are not significant
  • Zero Type 1 Space holding zeros on numbers less
    than one.
  • 0.00500
  • Zero Type 2 the zero to the left of the decimal
    point on numbers less than one.
  • When 0.00500 is written, the very first zero (to
    the left of the decimal point) is put there to
    communicate that the decimal point is a decimal
    point

57
More Zeros that are not significant
  • Zero Type 3 trailing zeros in a whole number.
  • 200 is considered to have only ONE significant
    figure while 25,000 has two
  • The zeros are simply place holders
  • Zero Type 4 leading zeros in a whole number.
  • 00250 has two significant figures
  • 005.00 x 104 has three

58
Special Cases
  • Exact numbers, such as the number of people in a
    room, have an infinite number of significant
    figures
  • Exact numbers are counting up how many of
    something are present, they are not measurements
    made with instruments
  • Another example of this are defined numbers, such
    as 1 foot 12 inches, there are exactly 12
    inches in one foot

59
Practice Problems
  • 1) 3.0800
  • 2) 0.00418
  • 3) 7.09 x 105
  • 4) 91,600
  • 5) 0.003005
  • 6) 3.200 x 109
  • 7) 250
  • 8) 780,000,000
  • 9) 0.0101
  • 10) 0.00800
  • http//dbhs.wvusd.k12.ca.us/webdocs/SigFigs/SigFig
    sFable.html
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