SHS CHEMISTRY
Unit 2 Scientific Measurement
Chemistry, Wilbraham Chapter 3
Quantify Yourself!
Unit 2 LEQs
• Concept: Measurements and Uncertainty
– LEQ 1: How do the terms accuracy and precision relate to collecting data?
– LEQ 2: How do I utilize significant figures?
– LEQ 3: How do I utilize scientific notation?
• Concept: The International System
– LEQ 4: How does the SI system of units operate?
– LEQ 5: What are the units of temperature?
• Concept: Conversion Problems
– LEQ 6: How do I apply dimensional analysis to solve conversion problems?
• Concept: Density
– What methods can be used to derivethe density of a substance?
Concept: Measurements and Uncertainty
LEQ 1: How do the terms accuracy and precision relate to collecting data?
• Accuracy: Closeness of a datum or average of a set of data to an accepted value.
• Precision: The reproducibility or grouping of data.
Tools that standardize accuracy and precision in Chemistry
• Significant Figures
– Determine the confidence for a digit in a quantity.
• Scientific Notation
– Remove ambiguity from written quantities.
HW for tomorrow
Read over section R59‐R60
Measurements and Uncertainty
LEQ 2: How do I utilize significant figures?
• What is the purpose of sig figs?
– To show precision.
– To show confidence in a quantity – To make measurements and perform calculations the same way!
How do we do sig figs?
• Atlantic/Pacific Rule
– Absent decimal: Come from the Atlantic and count all digits after(and including) the first non‐zero.
• 230000
• 256300
(2 sig figs…only 2 and 3)
(4 sig figs…only non‐zero)
– Present Decimal: Come from the Pacific and count all digits after (and including) the first non‐zero.
•
•
•
•
0.00367
2.050
0.00300
2.00x103
(3 sig figs…3,6, 7)
(4 sig figs… all)
(3 sig figs… 3 and right 00)
(3 sig figs… all shown)
How do we use sig figs?
•Multiplication/Division
– The answer can have no more significant digits than the worst value in the calculation
– 2400 m x 2 m= 5 x 103 m2 but 2400 m x 2.0 m=4.8 x 103 m2
– 2400 g / 2 mL=1 x 103 g/mL but
2400 g / 2.0 cm3= 1.2 x 103 g/cm3
•Addition/Subtraction
– The answer will be to the same decimal place as the number in the original problem that has the least number of decimal places.
–
12.23
cm
12.01 mm
–
+ 1.236 cm
‐ 0.0100 mm –
13.466 12.0000
–
13.45 cm 12.02 mm
Measurements and Uncertainty
LEQ 3: How do I utilize scientific notation?
• How is scientific notation different from standard notation?
– Scientific notation simplifies numbers in standard notation by removing all powers of ten.
• Why use scientific notation in chemistry?
– In chemistry we use very large and small numbers… ex the diameter of a zinc atom is about 0.00000000002 m we can simply call this 2 x 10‐10 m. – the number of atoms in 12g of carbon is… 6022000000000000000000000 …or 6.022 x 1023 atoms
How do we do scientific notation?
• To represent a standard number in scientific notation we simply remove all powers of ten and show the value with two components; a coefficient ≥ 1 and < 10 (showing only significant figures) along with a power of ten.
Ex. 200 m …has two powers of ten in it
2 x 100 m
2 x 102 m
Use the chemistry skills practice to try a few.
How do we use scientific notation?
1.
2.
3.
4.
1.
2.
3.
4.
Multiplication
Multiply coefficients
Add Exponents
Perform Operation on Units
Adjust Coefficients for Sig Figs
Division
Divide Coefficients
Subtract Exponents
Perform Operation on Units
Adjust Coefficients for Sig Figs
1.
2.
3.
4.
5.
6.
Addition & Subtraction
Adjust Number so Units are the Same.
Adjust Decimal so Exponents are the same.
Add or Subtract Coefficient Carry Exponent and Units
Perform Sig Fig Operation
Adjust Coefficient (and exponent) to make sure it is ≥ 1 and < 10 .
The International System
LEQ 3: How does the SI system of units operate?
• What is SI?
– abbreviated SI from
the French le Système international d'unités
– Comprised of standard base units and power of 10 prefixes
– developed in 1960 – universally employed
Name
Symbol Quantity
metre
m
length
kilogram
kg
mass
second
s
time
ampere
A
electric current
kelvin
K
thermodynamic temperature
candela
cd
luminous intensity
mole
mol
amount of substance
Base 10 Prefixes
Name
Multi Symbo
ples l
deca‐ hecto‐ kilo‐ mega‐
giga
tera‐ peta‐ exa‐
‐
zetta yotta
‐
‐
da
h
k
M
G
T
P
E
Z
Y
Factor 100 101
102
103
106
109
1012
1015
1018
1021
1024
Name
deci‐
centi milli
nano
femto atto zepto yocto
micro‐
pico‐
‐
‐
‐
‐
‐
‐
‐
d
c
m
µ
n
p
f
10−1
10−2
10−3
10−6
10−9
10−12
10−15
Subd
Symbo
ivisio
l
ns
Factor
100
a
10−1
8
z
y
10−21 10−24
The International System
LEQ 4: What are the units of temperature?
• Ways to express temperature
– Fahrenheit (°F)
– Celsius (°C)
• °C = .556(°F ‐32)
– Kelvin (K)
• K = °C + 273.14
Experiment: Extrapolation of Absolute Zero
Conversion Problems
LEQ 5: How do I apply dimensional analysis to solve problems?
• Why use it?!
• To organize problem solving .
• To insure answer is in the correct units.
How do we use dimensional analysis?
•The speed of light in a vacuum is 3.00x108 m/s. Express this speed in miles per hour.
•Remember that “what goes up must come down”
3.00 x108 m 3600 s 1 mi
3.00 x108 x3600
x
x
=
s
1 hr 1609 m
1609
= 6.7122 x108 mi
hr
With correct significant digits : 6.71x108 mph
Density
What methods can be used to derive the density of a substance?
D = m/V
• Intensive or Extensive Property?
– Solids: g/cm3
• Ex. lead 11.4 g/cm3, Copper 6.97 g/cm3
– Liquids: g/mL
• Ex. Water 1.0 g/mL, oil 9.5 g/mL
– Gases: g/L3
• Air g/L3, Helium g/L3
Study Your KUD!