View
60
Download
3
Category
Preview:
DESCRIPTION
Unit 2. Measurement. Do Now. In your own words, what do you think is the difference between: Accuracy and Precision?. 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. - PowerPoint PPT Presentation
Citation preview
Unit 2. Measurement
Do Now In your own words, what do you think is the
difference between:
Accuracy and Precision?
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 = CORRECTPRECISE = CONSISTENT
ACCURATE = CORRECTPRECISE = CONSISTENT
B. Percent Error Indicates accuracy of a measurement
100literature
literaturealexperimenterror %
your value
accepted value
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 = 2.90 %
C. Significant Figures Indicate precision of a measurement. Recording Sig Figs
Sig figs in a measurement include the known digits plus a final estimated digit
C. Significant Figures Indicate precision of a measurement. Recording Sig Figs
Sig figs in a measurement include the known digits plus a final estimated digit
2.35 cm
C. Significant Figures Counting Sig Figs (Table 2-5, p.47)
Count all numbers EXCEPT:
Leading zeros -- 0.0025 (not significant)
Trailing zeros without a decimal point -- 2,500 (not Significant)
Zeros between numbers are significant
4. 0.080
3. 5,280
2. 402
1. 23.50
C. Significant FiguresCounting Sig Fig Examples
1. 23.50
2. 402
3. 5,280
4. 0.080
4. 0.080
3. 5,280
2. 402
1. 23.50
C. Significant FiguresCounting 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 figs
C. Significant Figures Calculating with Sig Figs
Multiply/Divide –
The # with the fewest sig figs determines the # of sig figs in the answer.
Multiplication and Division Rules Do the sum Round the answer to the least
significant figure in the problem
13.91g/cm3)(23.3cm3) = 324.103g 4SF 3SF 3SF
324g
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.
Addition and Subtraction Rules Stack the numbers so that the decimal
point is aligned Do the sum Figure out which number has least
decimal place (least precise/decimal area least far out)
Draw a line after the last number with the least decimal place
Round the digit by looking at the number that follows
Example
3.75 mL + 4.1 mL 7.85 mL 7.9 mL
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
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
D. Scientific Notation
Converting into Sci. Notation: Move decimal until there’s 1 digit to its
left. Places moved = exponent. Large # (>1) positive exponent
Small # (<1) negative exponent Only include sig figs.
65,000 kg 6.5 × 104 kg
D. Scientific Notation
7. 2,400,000 g
8. 0.00256 kg
9. 7 10-5 km
10. 6.2 104 mm
Practice Problems
D. Scientific Notation
7. 2,400,000 g
8. 0.00256 kg
9. 7 10-5 km
10. 6.2 104 mm
Practice Problems
2.4 106 g2.56 10-3 kg
0.00007 km62,000 mm
D. Scientific Notation Calculating with Sci. Notation
(5.44 × 107 g) ÷ (8.1 × 104 mol) =
5.44EXPEE
÷EXPEE ENTER
EXE7 8.1 4
= 671.6049383 = 670 g/mol = 6.7 × 102 g/mol
Type on your calculator:
E. Proportions Direct Proportion
Inverse Proportion
xy
xy 1
y
x
y
x
Units of Measurement
A. Number vs. Quantity Quantity - number + unit
UNITS MATTER!!
B. SI UnitsQuantity Base Unit Abbrev.
Length
Mass
TimeTemp
meter
kilogram
secondkelvin
m
kg
sK
Amount mole mol
Symbol
l
m
tTn
B. SI Unitsmega- M 106
deci- d 10-1
centi- c 10-2
milli- m 10-3
Prefix Symbol Factor
micro- 10-6
nano- n 10-9
pico- p 10-12
kilo- k 103
BASE UNIT --- 100
C. Derived Units Combination of base units.
Volume (m3 or cm3) length length length
D = MV
1 cm3 = 1 mL1 dm3 = 1 L
Density (kg/m3 or g/mL or g/cm3)
mass per volume
D. Density
Mas
s (g
)
Volume (cm3)
ΔxΔyslope D
VM
Problem-Solving Steps
1. Analyze
2. Plan
3. Compute
4. Evaluate
D. Density An object has a volume of 825 cm3 and a density of
13.6 g/cm3. Find its mass.
GIVEN:V = 825 cm3
D = 13.6 g/cm3
M = ?
WORK:
VMD
D. Density An object has a volume of 825 cm3 and a density of
13.6 g/cm3. Find its mass.
GIVEN:V = 825 cm3
D = 13.6 g/cm3
M = ?
WORK:M = DV
M = (13.6 g/cm3)(825cm3)
M = 11,200 gVMD
D. Density A liquid has a density of 0.87 g/mL. What volume is
occupied by 25 g of the liquid?
GIVEN:D = 0.87 g/mLV = ?M = 25 g
WORK:
VMD
D. Density A liquid has a density of 0.87 g/mL. What volume is
occupied by 25 g of the liquid?
GIVEN:D = 0.87 g/mLV = ?M = 25 g
WORK:V = M D
V = 25 g 0.87 g/mLV = 29 mLV
MD
III. Unit Conversions
A. SI Prefix Conversions1. Find the difference between the exponents of the
two prefixes.
2. Move the decimal that many places.
To the leftor right?
A. SI Prefix Conversionsmega- M 106
deci- d 10-1
centi- c 10-2
milli- m 10-3
Prefix Symbol Factor
micro- 10-6
nano- n 10-9
pico- p 10-12
kilo- k 103
mov
e le
ftm
ove
right
BASE UNIT --- 100
A. SI Prefix Conversions1) 20 cm = ______________ m
2) 0.032 L = _____________ mL
3) 45 m = ______________ nm
4) 805 dm = ______________ km
C. Johannesson
A. SI Prefix Conversions1) 20 cm = ______________ m
2) 0.032 L = ______________ mL
3) 45 m = ______________ nm
4) 805 dm = ______________ km
0.2
0.0805
45,000
32
33
cmgcm
B. Dimensional Analysis The “Factor-Label” Method
Units, or “labels” are canceled, or “factored” out
g
B. Dimensional Analysis Steps:
1. Identify starting & ending units.2. Line up conversion factors so units
cancel.3. Multiply all top numbers & divide by
bottom number.4. Check units & answer.
B. Dimensional Analysis Lining up conversion factors:
ARE THESE THE SAME?1 in = 2.54 cm
2.54 cm 2.54 cm
1 in = 2.54 cm 1 in 1 in
= 1
1 =
B. Dimensional Analysis
How many milliliters are in 1.00 quart of milk?
1.00 qt 1 L1.057 qt
= 946 mL
qt mL
1000 mL1 L
B. Dimensional Analysis You have 1.5 pounds of gold. Find its volume in cm3
if the density of gold is 19.3 g/cm3.
lb cm3
1.5 lb 1 kg2.2 lb
= 35 cm31000 g
1 kg1 cm3
19.3 g
B. Dimensional Analysis How many liters of water would fill a container that
measures 75.0 in3?
75.0 in3 (2.54 cm)3
(1 in)3= 1.23 L
in3 L
1 L1000 cm3
B. Dimensional Analysis
5) Your European hairdresser wants to cut your hair 8.0 cm shorter. How many inches will he be cutting off?
8.0 cm 1 in2.54 cm
= 3.2 in
cm in
B. Dimensional Analysis6) Taft football needs 550 cm for a 1st down. How
many yards is this?
550 cm 1 in2.54 cm
= 6.0 yd
cm yd
1 ft12 in
1 yd3 ft
B. Dimensional Analysis7) A piece of wire is 1.3 m long. How many 1.5-cm
pieces can be cut from this wire?
1.3 m 100 cm1 m
= 86 pieces
cm pieces
1 piece1.5 cm
Recommended