chapter 2: measurement and calculations… section 2-1: scientific method (pg29-31) will not be...
TRANSCRIPT
Chapter 2: Measurement and Calculations…
Section 2-1: Scientific Method (pg29-31) will not be explicitly covered but used
throughout this entire class…
1
Section 2-2: Units of Measurement & Metric review
and summary…Pgs 33-39
2
The Fundamental Metric System (SI) Units…some of them
Physical Quantity Name Abbreviation
Mass kilogram kg
Length meter m
Time second s
Temperature Kelvin K
Electric Current Ampere A
Amount of Substance mole mol
Luminous Intensity candela cd
SI Units
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SI (a.k.a. Metric system) PrefixesCommon to Chemistry
Prefix Unit Abbr. ExponentKilo k 103
Deci d 10-1
Centi c 10-2
Milli m 10-3
Micro 10-6
We will use these units primarily in this class, but these are only a few of the units within the SI (Metric System)
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KNOW THIS CHARTKNOW THIS CHART
(BIGGER) (smaller)mega-
(M)kilo-
(k)BASE UNIT
metergramLiter
deci-(d)
centi-(c)
milli-(m)
micro-(µ)
Even though there aren’t any prefixes that we need to use there, it’s important to remember
where the BLANK spaces are on this table.
Even though there aren’t any prefixes that we need to use there, it’s important to remember
where the BLANK spaces are on this table.
Group work/discussion…
• Get a white board and marker for the group…
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Density (review hopefully!...) Check out this picture on the right... •Which layer has the highest density?•Which layer has the lowest density?•Imagine that the liquids have the following densities:
– 10g/cm3.– 3g/cm3.– 6g/cm3.– 5g/cm3.
•Which number would go with which layer?
Density…• Density is defined as the ratio of
mass (matter) to volume.• Density (D) is usually expressed
D = m/v• Units are most commonly g/ml or
g/cm3 , but can be in ANY units of mass to volume!
• Density is a characteristic physical property that does not change with size of sample (BUT some conditions can affect density value…like what?)
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Conversion Factors (pg 40-42)
• We’ll cover this soon…not yet.
10
(p. 44 - 57)
Section 2-3: Using Scientific Measurements
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A. Accuracy vs. Precision• Accuracy - how close a measurement is to the
accepted value
• Precision - how close a series of measurements are to each other
ACCURATE = CORRECT
PRECISE = CONSISTENT12
B. Percent Error
• Indicates accuracy of a measurement
100literature
literaturealexperimenterror %
your value
accepted value13
B. Percent Error• A student determines the density of a substance to
be 1.40 g/mL. Find the % error if the accepted value of the density is 1.36 g/mL.
100g/mL 1.36
g/mL 1.36g/mL 1.40error %
% error = 2.9 %
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C. Significant Figures
• Indicate precision of a measurement.
• Recording measurements in Sig Figs…– Sig figs in a measurement include the known digits
plus a final estimated digit
2.35 cm
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C. Significant Figures
• Counting Sig Figs (textbook Table 2-5, p.47)
– Zeros that are in between any digits 1-9 are ALWAYS counted as significant
• Ex: 105 = 3 sig figs
1208.5 = 5 sig figs
– Count all numbers (1 though 9) EXCEPT…
• Leading zeros -- 0.0025
• Trailing zeros without a decimal point -- 2,500
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4. 0.080
3. 5,280
2. 402
1. 23.50
C. Significant Figures
Counting Sig Fig Examples
1. 23.50
2. 402
3. 5,280
4. 0.080
4 sig figs
3 sig figs
3 sig figs
2 sig figs17
C. Significant Figures
• Calculating with Sig Figs– Multiply/Divide - The # with the fewest sig figs
determines the # of sig figs in the answer.
(13.91g/cm3)(23.3cm3) = 324.103g
324 g
4 SF 3 SF3 SF
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C. Significant Figures
• Calculating with Sig Figs (con’t)– Add/Subtract - The # with the lowest decimal value
determines the place of the last sig fig in the answer.
3.75 mL
+ 4.1 mL
7.85 mL
224 g
+ 130 g
354 g 7.9 mL 350 g
3.75 mL
+ 4.1 mL
7.85 mL
224 g
+ 130 g
354 g 19
C. Significant Figures
• Calculating with Sig Figs (con’t)– Exact Numbers do not limit the # of sig figs in the answer.
• Counting numbers: 12 students• Exact conversions: 1 m = 100 cm• “1” in any conversion: 1 in = 2.54 cm
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C. Significant Figures
5. (15.30 g) ÷ (6.4 mL)
Practice Problems
= 2.390625 g/mL
18.1 g
6. 18.9 g
- 0.84 g18.06 g
4 SF 2 SF
2.4 g/mL2 SF
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D. Scientific Notation (and standard notation)
• PROPER Sci. notation uses format: M x 10n
– M is larger than 1 and smaller than 10 (1.000 to 9.999)
• To converting into Sci. Notation:
– Move decimal until there’s 1 digit to left of decimal (COUNTING places moved tells you about the exponent)
– Large numbers (>1) positive exponentsSmall numbers (<1) negative exponent
– Only include sig figs. (significant figures)
65,000 kg 6.5 × 104 kg
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D. Scientific Notation
• 2,400,000 g
• 0.00256 kg
• 7 10-5 km
• 6.2 104 mm
Practice Problems
2.4 106 g
2.56 10-3 kg
0.00007 km
62,000 mm23
D. Scientific Notation
• Calculating with Sci. Notation
(5.44 × 107 g) ÷ (8.1 × 104 mol) =
5.44EXPEXP
EEEE÷÷
EXPEXP
EEEE ENTERENTER
EXEEXE7 8.1 4
= 671.6049383 = 670 g/mol = 6.7 × 102 g/mol
Type on your calculator:
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E. Proportions
• Direct Proportion
Inverse Proportion
xy
xy
1
y
x
y
x 25