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Aim:
How Can We Make
Measurements in the
Laboratory
Accuracy Vs. Precision
Accuracy
How close a
measurement is
to the true,
accepted value.
Precision
How close
measurements
are to one
another.
Quantitative vs. Qualitative
Measurements
• Qualitative Measurements gives data in a
descriptive, non-numeric form.
– Example: “This person feels feverish.”
• Quantitative Measurements gives data in
a definite form, usually as numbers.
– Example: “This person’s temperature is 100.3
degrees Fahrenheit.”
Percent Error
% Error = Observed Value – True Value x 100
True Value
Percent error helps us to determine the accuracy and
precision of our chemical data.
Where can you find this formula in your Reference
Tables?
Percent Error Example
% Error = Observed Value – True Value x 100
True Value
A student determined the boiling point
of a substance to be 62.5 oC. If the
accepted value is 58.1 oC, what is the
percent error?
Accuracy vs. Precision
“Lab”
Do Now:
1.Hand in safety contract, safety letter, and
questionnaire.
2. Put your name on testing folder, insert
calculator, reference table, pens, and pencils.
3. Accuracy & precision activity due on
Wednesday, 9/11.
4. Quiz on Thursday, 9/12.
5. Homework packet #1 due next Tuesday, 9/17.
6. Fill in your name on the seating chart.
Aim:
How do scientists use the
metric system and
scientific notation to
make calculations?
The Powers of Ten
Picture a microscopic
cell…
Picture the
galaxy...
Scientists need a way to express extremely large and
extremely small numbers in their quantitative
measurements.
Scientific Notation
• Scientific notation allows scientists to
express extremely large and extremely
small numbers in their measurements
• Scientific notation shows the product of
two numbers:
(a coefficient) x (10 to some exponent)(units)
a number between 1 and 10 that
you multiply an expression by
10 multiplied by itself that many
times; example: 103 = 10 x 10 x 10
Expressing Very Large
Numbers…
• Do you recognize this number?
300,000,000 m/sec
• Express the speed of light using scientific
notation (the product of two numbers):
(a coefficient) x (10 to some exponent)(units)
8
3
x
10
m/sec
Expressing Very Small
Numbers…
• Do you recognize this number?
.000000000753 kg
• Express the mass of a single dust particle
using scientific notation:
(a coefficient) x (10 to some exponent)(units)
-10
7.53
x
10
kg
Try some on your own…
1. 0.000008 meters = ______________
2. 457,000 Joules = ________________
3. 65 grams = _____________________
SI Units
(“Le Systeme International d’Unites”)
• Scientists express quantitative measurements using SI
units.
D in your Reference Tables to find a list of the
– Use Table _____
SI Units we will be using.
• Selected base SI units:
gram (g)
– mass: _____________
liter (L)
– volume: ___________
meter (m)
– distance: _______________
Kelvin (K)
– temperature: _____________
Joule (J)
– heat energy: ______________
• Prefixes combine with base units to indicate fractions or
multiples of a unit.
– Examples: kilo, hecto, milli, centi
So… Why SI Units?
So… Why SI Units?
Comparing English units of length to SI units of length..
English Conversions
12 inches = 1 foot
3 feet = 1 yard
1760 yards = 1 mile
SI Conversions
10 centimeters = 1
decimeter
10 decimeters = 1 meter
10 meters = 1 dekameter
Think about it…
•Which would you rather memorize?
•Which would you rather use in calculations?
So… Why SI Units?
Comparing U.S. units of volume to SI units of volume ..
U.S. Conversions
8 ounces = 1 cup
2 cups = 1 pint
2 pints = 1 quart
4 quarts = 1 gallon
SI Conversions
1000 cubic millimeters = 1 cubic
centimeter
1000 cubic centimeters = 1 cubic
decimeter
1000 cubic decimeters = 1 cubic
meter
1000 cubic meters = 1 cubic
dekameter
Converting Between SI Units Using
the Ladder Method
Kilo
(k)
Hecto
(H)
Deca
(D)
When you go up the
steps..move decimal
point to the left
Base
Unit
When you go down the
steps, move decimal
point to the right
deci
(d)
centi
(c)
milli
(m)
Metric Conversion Practice
• How many kg (kilograms) are there in 5276.4 g
(grams)? ______________________________________
Kilo
(k)
Hecto
(H)
Deca
(D)
Base
Unit
deci
(d)
centi
(c)
milli
(m)
Metric Conversion Practice
• How many mm (millimeters) are in 160 cm
(centimeters)? ______________________________________
Kilo
(k)
Hecto
(H)
Deca
(D)
Base
Unit
deci
(d)
centi
(c)
milli
(m)
Metric Conversion Practice
• How many L (liters) are in 2534 mL (milliliters)?
______________________________________
Kilo
(k)
Hecto
(H)
Deca
(D)
Base
Unit
deci
(d)
centi
(c)
milli
(m)
Metric Conversion Practice
• How many meters are in 1 cm?
______________________________________
Kilo
(k)
Hecto
(H)
Deca
(D)
Base
Unit
deci
(d)
centi
(c)
milli
(m)
Aim:
How can we use
dimensional analysis
(factor-label method) to
convert between units?
Dimensional Analysis
(a.k.a. The Factor-Label Method)
• We use dimensional analysis to convert
from one unit to another.
Equivalence Statement
Equivalence Statement: the relationship
between two different units
Examples:
1 foot = 12 inches
1 hour = 60 minutes
1 dozen = 12 eggs
1 kilometer = 1000 meters
Selected Equivalence
Statements
1000
1L = ____________mL
1
1000 g = ____________Kg
1
cm3
1
= ______mL
101.3
1 atm = _____________kPa
Conversion Factors
Conversion Factor: A relationship
between two different units in a
fraction form.
Example:
1 dozen or 12 eggs
12 eggs
1 dozen
Steps of Factor-Label Method
1.
2.
3.
4.
5.
Write down the units you are given.
Write “X” and draw a line.
Write given unit on the bottom of the line.
Write the desired unit on the top of the line.
Find and plug in your conversion factor.
(Hint: the larger unit will always get a 1
next to it!)
6. Cancel units and do the math.
7. Voila! 
Let’s do one together…
• Convert 90 minutes to hours.
90 minutes = _______ hours
hour = Desired
Starting Units x Desired1 units
90
min
X
=
1.5
hours
1
Starting
Units
60units
min
1 hour = 60 minutes
Let’s do one together…
• Convert 0.600 liters to milliliters.
0.600L = _______mL
Starting Units x Desired
1000units
mL = Desired
= 600
mL
1 0.600L X
Starting1 units
Units
L
1 L = 1000mL
Let’s do one together…
How many kilograms are there in 5276.4 grams?
5276.4g = _______kg
Starting Units x Desired units
1 kg= Desired
X
= Units
5.276 g
1 5276.4gStarting
units
1000 g
1 kg = 1000g
TRY THE REST ON YOUR OWN !!!!
How about a challenge?!
How old are you? Convert your age in years to your age
in hours. Hint: you will need to do this in TWO steps.
Years  Days and then Days  Hours
26 years = _______ days
_____ days = ________ hours
How about a challenge?!
If an animal were to consume exactly 25g of food each
day, how many kg of food would it consume in one
year?
25 g/day = _______kg/year
25 Units
g
1 kg units
365
days
Starting
x
Desired
=
Desired
X
X
= 9.125
1
Starting
1000
g units1 year Units
day
kg/year
1 kg = 1000g
1year = 365 days
TRY THE REST ON YOUR OWN !!!!
Aim:
How can we count
significant figures
accurately?
Significant Figures
• Significant figures describe all digits in a
measurement that are certain, plus one
digit that is an estimate.
How long is this line?
• When we measure something, we always
estimate between the smallest marks, one
place further than we know for sure.
4.5 cm
estimate
Uncertainty in Measurement
• The better the measuring device the better
we can estimate.
4.55 cm
estimate
Uncertainty in Measurement
• What is the total mass on this balance?
______ g + _____ g + _____ g + _____ g =
___________________ g
Rules for Counting Significant
Figures
• Rule #1: All non-zero digits are
significant.
4
• Ex: 125.7 g = ___________ sig figs
3
• Ex: 5.45 mL = __________
sig figs
Rules for Counting Significant
Figures
• Rule #2: “Sandwich Rule” – Zeros
between non-zero digits are significant.
3
• Ex: 405 mm = ___________
sig figs
4
• Ex: 20.06 mL = __________
sig figs
6
• Ex: 1002.05 g = __________
sig figs
Rules for Counting Significant
Figures
• Rule #3: “Leading Zeros Rule” – Zeros
that are placeholders in a measurement
are not significant.
2
• Ex: .0054 g = ___________
sig figs
3
• Ex: .0702 cm = __________
sig figs
Rules for Counting Significant
Figures
• Rule #4: “The Right-Right Rule” - In
measurements with a decimal, zeros to the
right of the decimal and to the right of nonzero digits are significant.
6
• Ex: 124.50 g = ___________
sig figs
5
• Ex: .38000 cm = __________
sig figs
Rules for Counting Significant
Figures
• Rule #5: “Trailing Zeros” – Zeros in a
number with no decimal point are not
significant.
2
• Ex: 5600 kg = ___________
sig figs
4
• BUT… 5600. kg = __________
sig figs
Here’s a Shortcut…
Decimal Present: Start
at Pacific (left) and
begin counting with
first non-zero digit.
Ex: 0.00234
Decimal Absent: Start
at Atlantic (right) and
begin counting with
first non-zero digit.
Ex: 1,000
Practice Problems:
Either on Nearpod or on Looseleaf
1.
2.
3.
4.
5.
6.
7.
8.
0.0278 m =
1.3 cm =
1.00 M =
8021 L =
0.2003 g =
56.000 kg =
120 cm3 =
0.000008075 =
3
___________
2
___________
3
___________
4
___________
___________
4
5
___________
2
___________
4
___________
Re‐write the quantity
827,000,000,000,000
picoseconds to show:
a) 1 sig. fig.
14
8
x
10
ps
________________________________
b) 2 sig. figs.
8.3 x 1014 ps
_________________________________
c) 3 sig. figs.
8.27 x
14
10 ps
_________________________________
Rewrite the quantity
0.0031904 kg to show:
a) 1 sig. fig.
-3
3
x
10
kg
_______________________________
b) 2 sig. figs.
-3
3.2 x 10 kg
_______________________________
c) 3 sig. figs.
-3
3.19
x
10
kg
_______________________________
How Do We....
Determine the number of
significant figures in measured
values when doing various
mathematical computations ?
Multiplication & Division
5.282
x 3.42
18.1
The answer should be rounded
off to contain the same
number of digits as found in
the factor with least
number of significant
figures.
Addition & Subtraction
11.31
33.264
+ 4.1
48.7
The answer should be the
rounded off so as to contain
the same number of decimal
places as the number with
the least number of
decimal places.
Record your answer to the correct
number of significant digits
• 1.23 x 400.0 =
492
• 1.2 + 0.345 = 1.5
• 640 ÷ 5.0 = 128
• 450.5 – 325.10 = 125.4
QUIZ REVIEW!
• Name that tool…
beaker tongs
test tube holder
QUIZ REVIEW!
• Name that tool…
wire gauze
clay triangle
QUIZ REVIEW!
• Name that tool…
wash bottle
Bunsen burner
QUIZ REVIEW!
• Name that tool…
graduated
cylinder
beaker
test tube
Erlenmeyer
flask
QUIZ REVIEW!
• Convert these units…
 500 mL to L
 .300 m to cm
0.5 L
30.0 cm
QUIZ REVIEW!
• Calculate the percent error…!
–Erica measures an eraser and finds its
mass to be 34.2 grams. Ms. Roman
says its mass is 36.6 grams. What is
Erica’s percent error?
QUIZ REVIEW!
•LAB SAFETY!!!