Chapter 2 Introductory Chemistry Measurements and Calculations

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Chapter 2Introductory Chemistry Measurements
and Calculations

• Objectives
• 1) To define measurement
• 2)To show how very large or very small numbers
  can be expressed in scientific notation

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Demonstration

• Number Line

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Measurement

• Quantitative observation

Every measurement
-number -and a unit
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Scientific Notation

• Scientific notation expresses a number as a
  product of a number between 1 and 10 and the
  appropriate power of 10.
• Example 93,000,000 9.3 x 107

0.0000167 1.67 x 10-5
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Scientific Notation
2.38x 105
0.00043 0.089 0.135 0.0024 0.104 0.0306 0.00000072
238,000 1,500,000 12,500 247 10 3,500,000 1430
4.3 x 10-3
1.5 x 106
8.9 x 10-2
1.35 x 10-1
1.25 x 104
2.4 x 10-3
2.47 x 102
1.04 x 10-1
1.0 x 101
3.06 x 10-2
3.5 x 106
1.43 x 103
7.2 x 10-7
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Units

• Objectives To learn the English, metric, and SI
  systems of measurement

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Units

• Measure the following strings
• Group A mm
• Group B cm
• Group C m
• Group D inches
• Group E feet

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Units

• Units part of a measurement that tells us what
  scale or standard is being used.
• Two main systems are used
• English system (United States)
• Metric system (used in most of the world)
• In 1960, INTERNATIONAL system(le Systeme
  Internationale) (SI) for scientists

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Units

• Fundamental SI Units
• Physical Quantity Name of Unit
  Abbreviation
• mass kilogram kg
• length meter m
• time second s
• temperature kelvin K

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Table 5.2
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Measurements of Length, Volume, and Mass

• Objectives To use the metric system to measure
  length, volume, and mass

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Table 5.3
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LengthFigure 5.1 Comparison of English and
metric units.
1 inch 2.54 cm
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Figure 5.2 Cube representations.
Volume the amount of 3D space occupied by a
substance.
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Figure 5.3 A 100 mL graduated cylinder.
Volume ( in a laboratory)
Beaker (inaccurate)Pipet Biuret Volumetric Flask
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Mass

• Mass is the quantity of matter present in an
  object.

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Uncertainty in Measurement

• Objectives
• To learn how uncertainty in a measurement arises.
• To learn to indicate a measurements uncertainty
  by using significant figures.

Homework Self-check exercise 5.2 p. 126
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Figure 5.5 Measuring a pin.
Tell me the length of the pin. Estimate the last
number
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Uncertainty in Measurement

• The first 2 digits are certain. The third digit
• is estimated and can vary. (uncertain number)
• 2.8

A measurement always has some degree of
uncertainty.
Certain numbers
Depends on the type of measuring device
SIGNIFICANT FIGURES all the certain numbers
plus the first uncertain number
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Significant Figures

• Rules for Counting Significant Figures
• All nonzero integers are significant. (1437)
• Zeroes
• Leading zeroes precede all nonzero are not
  significant (0.000025)
• Captive zeroes between all nonzero are
• significant (0.205)
• Trailing zeroes right end of number. Significant
  if number is written with a decimal point
• 100 (1 significant figure) 100. (3)
• 3) Exact numbers (determined by counting) have an
  unlimited number of significant figures in a
  calculation
• 1 inch2.54 cm. Neither limits the number of
  significant figures

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Significant Figures Practice
3 4 3 1 3 2

• The mass of a single eyelash is 0.000304
• The length of a skidmark is 1.270 x 102
• A 125-g sample of chocolate chip
• Cookies contains 10g of chocolate.
• The volume of soda remaining in a can after a
  spill is 0.09020 L.
• A dose of antibiotic is 4.0 x 10-1

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Significant Figures Practice

• A sample of orange juice contains 0.0108 g of
  Vitamin C
• A forensic chemist in a lab weighs a single hair
  and records its mass as 0.0050060
• The distance between 2 points was found to be
  5.030 x 103
• In yesterdays race 110 riders started but only
  60 finished.

3 5 4 unlimited
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Rounding off Numbers

• When you use your calculator, you get more
  numbers than are significant so you must round
  off.

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Rounding off Numbers

• Rules
• If the digit to be removed
• Is less than 5, the digit remains the same
• If its or gt 5, the preceding digit increases.
• 2) In a series of calculations, carry the extra
  digits to the final calculation and then round
  off.

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Rounding off

• If you round off to 2 significant digits
• 4.348 4.3
• Use only the first number to the right of the
  last significant figure.

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Determining Significant Figures in Calculations

• For multiplication/division of significant
  figures the smallest number of significant
  figures (Measurement is limiting)
• Example 4.56 x 1.4 6.384 6.4
• 8.315/298 0.0279027 0.0279

2 significant figures
3 significant figures
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Determining Significant Figures in Calculations

• For addition and subtraction limiting term is
  one with the smallest number of decimal places.
• 12.11 0.6875
• 18.0 -0.1
• 1.013 0.5875 0.6
• 31.123 31.1

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Practice with Calculations

• 5.19 1081 2.3 x 3.14
• 1.9 - 7.25 3 boxes of candy
• 0.842 _at_2.50
• 17.1
• 0.77
• 241

Do self-check exercise p.129 Homework Focus
Questions p. 129
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Density

• Objective To define density and its units

Homework Self-check exercise 5.4 p. 133
Self-check exercise 5.5 p. 134
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Density

• Density can be defined as the amount of matter
  present in a given volume.
• Density mass
• volume
• Specific gravity is the ratio of the density of a
  given liquid to the density of water at 4 C.

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Problem Solving and Dimensional Analysis

• Objective To learn how dimensional analysis can
  be used to solve various types of problems.
• Unit1 x conversion factor Unit 2
• Equivalence statement 1 inch 2.54 cm
• Converting from one unit to another is often
  called dimensional analysis.

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Rules for Converting

• Step 1 Use the equivalence statement.
• Step 2 Choose the conversion factor by looking
  at the direction of the required change.
• Step 3 Multiply the quantity to be converted by
  the conversion factor
• Step 4 Check for significant figures
• Step 5 Ask whether your answer makes sense

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Practice Problems

• A new baby weighs 7.8 lbs. What is its mass in
  kilograms?
• A piece of lumber is 88.4 cm long. What is its
  length in mm? in inches?
• A bottle of soda conains 2.0 L What is the
  volume in quarts?

p.132
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Chapter 2 Temperature Conversions

• Objectives To learn the three temperature
  scales.
• 2) To learn to convert from one scale to another
• 3) To continue to develop problem-solving skills

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Figure 5.6 The three major temperature scales.
The size of each temperature unit is the same for
the Celsius and Kelvin scale.
The size of each unit Is lt Celsius/Kelvin.
Zero point is different on all 3 scales.
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Converting from Celsius to Kelvin
Temp oC 273 Temp oK
Temp oK- 273 Temp oC
The temperature is a balmy 28.5 oC. Convert it to
the Kelvin scale. The freezing point of Nitrogen
is -210 oC. What is the temperature on the Kelvin
scale?
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Figure 5.8 Comparison of the Celsius and
Fahrenheit scales.
Celsius to Fahrenheit Temp in Fahrenheit 1.8
(Temp in Cel) 32 Fahrenheit to Celsius Temp in
Celsius Temp in Fahrenheit -32
1.8
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Practice Problems

• Self check exercise 5.7 and 5.8 p. 140-141
• Focus questions p.146 1-5
• Complete for Homework

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Figure 5.9 Tank of water.
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Figure 5.9 Person submerged in the tank.