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Honors Chemistry, Chapter 2 Page 1 Chapter 2 – Measurements and Calculations
Honors Chemistry, Chapter 2Page 1
Chapter 2 – Measurements and Calculations
Honors Chemistry, Chapter 2Page 2
Evidence of Chemical Change
• Evolution of a Gas (Bubbles, Odor)
• Formation of a Precipitate (Formation of Cloudiness in a Clear Solution, Solids Collecting at the Bottom or Top)
• Release of Energy (Heat, Light)
• Color Change
Honors Chemistry, Chapter 2Page 3
Scientific Method
• Observing and Collecting Data– Qualitative (Bubbles Formed)– Quantitative (1 gram/liter of catalyst speeded
the reaction by 25%)– Chemists Study Systems (Region Selected for
Study)
• Formulate Hypothesis – Generalization about Data – Testable Statement
Honors Chemistry, Chapter 2Page 4
Scientific Method
• Testing Hypothesis (Experimentation)– Supported, Retained– Not Supported, Discarded, Modified
• Theorizing – Create a Model– Model: An Explanation of How Phenomena
Occur and How Data or Events are Related.• Visual• Verbal• Mathematical
Honors Chemistry, Chapter 2Page 5
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(Wisdom is essential in a
president, the appearance of
wisdom will do in a candidate. –
Eric Severeid)
Honors Chemistry, Chapter 2Page 6
Units of Measure
• Measurements Are Quantitative Information
• Quantity: Something That Has Size or Amount
Honors Chemistry, Chapter 2Page 7
SI Measurement
• SI Units Are Defined in Terms of Standards of Measurement
• Seven Basic Units
• All Others Derived From Seven Basic Units
Honors Chemistry, Chapter 2Page 8
SI Base UnitsQuantity Symbol Unit Abbreviation
Length l meter m
Mass m Kilogram Kg
Time t second s
Thermodynamic Temperature T Kelvin K
Amount of a Substance n mole mol
Electric Current I ampere ALuminous Intensity Iv candela cd
Honors Chemistry, Chapter 2Page 9
SI Prefixes
Prefix AbbreviationExponent Multiplier Meaning Example Using Length
tera- T 10121000000000000 1 terameter (Tm)
giga- G 1091000000000 1 gigameter (Gm)
mega- M 1061000000 1 megameter (Mm)
kilo- k 1031000 1 kilometer (km) = 1000 m
hecto- h 102100 1 hectometer (hm) = 100 m
deka- da 10110 1 dekameter (dam) = 10 m
1001 1 meter (m)
Honors Chemistry, Chapter 2Page 10
SI Prefixes
Prefix AbbreviationExponent Multiplier Meaning Example Using Length
1001 1 meter (m)
deci- d 10-10.1 1 decimeter (dm)
centi- c 10-20.01 1 centimeter (cm)
milli- m 10-30.001 1 millimeter (km)
micro- 10-60.000001 1 micrometer (m)
nano- n 10-90.00000001 1 nanometer (nm)
pico- p 10-120.000000000001 1 picometer (pm)
Honors Chemistry, Chapter 2Page 11
Derived Units
• Area A m2
• Volume V m3
• Density D kg/m3 (=m/V)
• Molar Mass M kilograms/mol
• Concentration c mol/liter
• Molar Volume Vm m3/mol
• Energy E joule
Honors Chemistry, Chapter 2Page 12
Helpful Hint
• Relationship Between D, m, and V:
D
m
V
Honors Chemistry, Chapter 2Page 13
Factor Label Method
• Express 4.5 kg as grams• Begin by Expressing as a Fraction: 4.5 kg
1• Identify Conversion Factor: 1 kg = 1000 grams• Express as a Fraction:
1 kg 1000 g1 = --------------- or -------------- 1000 g 1 kg
Honors Chemistry, Chapter 2Page 14
Factor LabelContinued
• Write Equation Including Proper Factor
• Cancel Units
• Multiply Numbers to Get Final Result
4.5 kg 1000 g--------- x -------------- = 4500 g 1 1 kg
Honors Chemistry, Chapter 2Page 15
Scientific Measurements
• Accuracy – The Closeness of Measurements to the Correct or Accepted Value
• Precision – The Closeness of a Set of Measurements
Honors Chemistry, Chapter 2Page 16
Accuracy vs. Precision
XXXX
XXXX
High Precision
High Accuracy
High Precision
Low Accuracy
Honors Chemistry, Chapter 2Page 17
Accuracy vs. Precision
X X
X X
X X
X X
Low Precision
Low Accuracy
Low Precision
High Accuracy
(on average)
Honors Chemistry, Chapter 2Page 18
Percent Error
Valueaccepted - Valueexperimental
%Error = ---------------------------------------
Valueaccepted
Honors Chemistry, Chapter 2Page 19
Significant Figures
• All the Digits Known With Certainty Plus One Final Digit Which is Somewhat Uncertain
| I I I I | I I I I | I I I I | I I I I |
7 8 9
8.36
Honors Chemistry, Chapter 2Page 20
Rules for Significant Figures
1. Zeros Appearing Between Nonzero Digits are Significant
2. Zeros Appearing in Front of All Nonzero Digits are Not Significant
3. Zeros Appearing to the Right of the Decimal Point And at the End of the Number are Significant
Honors Chemistry, Chapter 2Page 21
Rules for Significant Figures
4. Zeros at the End of a Number but to the Left of the Decimal Point May or May Not be Significant. If a Zero Has Not Been Measured or Estimated but is Just a Placeholder, it is Not Significant. A Decimal Point Placed After Zeros Indicates They are Significant.
Honors Chemistry, Chapter 2Page 22
Rules for Rounding
If the Digit Following the Last Digit to be Retained is:
> 5 Then Round Up
< 5 Then Round Down
5 Followed by non Zero Digits
Then Round Up
Honors Chemistry, Chapter 2Page 23
Rules for Rounding
If the Digit Following the Last Digit to be Retained is:
5 Followed by Non-Zero Digit(s), and Preceeded by an Odd Digit
Round Up
5 Followed by Non-Zero Digit(s), and
Preceeded by an Even Digit
Leave Unchanged
Honors Chemistry, Chapter 2Page 24
Significant Figures With Addition/Subraction
• When Adding or Subtracting Decimals, the Answer Must Have the Same Number of Digits to the Right of the Decimal Point as There are in the Measurement Having the Fewest Digits to the Right of the Decimal Point.
Honors Chemistry, Chapter 2Page 25
Significant Figures With Multiplication/Division
• When Multiplying or Dividing, the Answer Can Have no More Significant Figures Than are in the Measurement with the Fewest Number of Significant Figures.
• (Conversion Factors Have Unlimited Digits of Accuracy.)
Honors Chemistry, Chapter 2Page 26
Scientific Notation
• Move the Decimal Point Left or Right Until the Mantissa is Greater Than or Equal to 1.0 and Less Than 10
• Express the Number as: M x 10n Where n Represents the Number of Places the Decimal Point was Moved, Positive if the Decimal is Moved Left and Negative if the Decimal is Moved Right
Honors Chemistry, Chapter 2Page 27
Direct Proportion
• Y = kX
• Example Mass vs. Volume Data for Aluminum
• Slope of the Line (k) is the Density
Honors Chemistry, Chapter 2Page 28
Measurement of a Series of Blocks
Block Number Mass (g) Volume (cm3)
1 1.20 0.442 3.69 1.393 5.72 2.104 12.80 4.685 15.30 5.716 18.80 6.907 22.70 8.458 26.50 9.649 34.00 12.80
10 36.40 13.50
Honors Chemistry, Chapter 2Page 29
Plot Mass vs. Volume
Mass (g) As a Function of Volume (V)
0
5
10
15
20
25
30
35
40
0 5 10 15
Volume - cubic centimeters
Ma
ss
- g
ram
s
Mass (g)
Honors Chemistry, Chapter 2Page 30
Calculate Slope and Intercept
• Y = mX + b= slope x Volume + intercept
• Slope = 2.69 g/cm3
• Intercept = 0.09 grams (!) (Actually Zero)
• From Table of Densities: Sample is Aluminum (Al)
Honors Chemistry, Chapter 2Page 31
Inversely Proportional
• k = XY or Y = k/X
• As X Increases, Y Decreases
• Example: Pressure-Volume Data
Honors Chemistry, Chapter 2Page 32
Pressure Volume Data for Nitrogen
Pressure (k-Pa) Volume (cm3) P x V
100 500 50000150 333 49950200 250 50000250 200 50000300 166 49800350 143 50050400 125 50000450 110 49500
Honors Chemistry, Chapter 2Page 33
Volume vs. Pressure For Nitrogen
0
100
200
300
400
500
600
0 200 400 600
Pressure (kPa)
Vo
lum
e (
cm
3)
Volume (cm3)
