Download chemistry unit 1 - measurement

Learning Goals – Part One
• Identify 3 main reasons for measurement
• Describe what is meant by the capacity and the
precision of a measurement tool
• Differentiate between certain and estimated
values in a measurement
• Record a measurement using the correct number
of significant digits
• Identify the number of significant digits in a given
measurement or calculated number
• Convert numbers from standard notation to
scientific notation and back
Chemistry
• Study of matter and the
changes or interactions
related to it
• Matter is anything that is
made up of atoms or
molecules which has mass
( particles ) and volume
(space) , it does not include
forms of energy
3 Good Reasons for Measurement
Related to Matter
1. Health and Safety
2. Environmental Impact
3. Economic concern
Health and Safety
Protective Devices, Measurement Devices,
Medical Doses
Environmental Impact
Pollution Control and Measurement of Contaminants
in the Air, Water, and Soil
Economic Concerns
Manufacturing , Waste Disposal, Water Treatment
Can Affect Tax Base of a Region, Profitability of a
Manufacturer or a Service Business
Precision and Capacity of Tools
• Precision
– What is the value of the
smallest certain value
(increment)
– Usually it will be some
factor of 10 for metric
units
– The smaller the value of
the increment, the
greater the precision
• Capacity
– What is the maximum
that can be measured
with certainty
– Usually it will be marked
on the tool in addition to
being the last certain
line
– Typically, the greater the
capacity, the lesser the
precision
What are Significant Figures?
What is their Purpose?
Numbers correctly recorded by
measurements always
communicate:
a) How exact the measurement is
b) How certain/uncertain we are
of the amount measured.
Significant digits Definition:
All of the digits from a
measurement that are known for
certain plus one placeholder that
is estimated
The last digit of a correctly
measured amount is always an
estimated value to communicate
the uncertainty in the amount
measured. (the next decimal
placeholder to the right of the last
one of which you are certain)
Reportable Measurement Values
Certain value:
value of each
NUMBERED line
Certain value:
value of each
NON-numbered
line
Estimated value:
value of space
between lines on
tool
.01 cm
.1 cm
1 cm
The length of the red
box = 2.35 cm
*The 5 is estimated
Reading Graduate Cylinders
Reported measurment = _______________g
32.6mL
8.45mL
33.5mL
Precision =
0.1mL
4.00cm
Reading Instruments with Significant
Digits Worksheet from Last Rotation
• Review each measurement you recorded and
make sure you have included ALL significant
digits
• Identify the precision of the tool
• Underline the estimated value in the reported
measurement
Significant Figures in Measurement
• All reported measurements must include ALL
certain values and ONE final estimated value
• The number of significant figures in a reported
measurement will INCLUDE all certain values
and ONE final estimated value
• The number of significant figures AFTER the
decimal MUST be the same for all
measurements with the same tool/instrument
The Precision of an Instrument is based on
the value of the Estimated Number
• Precision is reported as a factor, not an actual
number, attached to a unit
– 10mL, 1mL, 0.1cm, 0.01g, 0.001cm, etc.
• The smaller the value of the estimated number,
the greater the precision of the tool/instrument
• All derived units (those determined by calculation
with 2 or more measurements) must be reported
with a value for the estimated number for the
least accurate measurement unless instructed
otherwise.
When analyzing a number, what digits
are Significant?
 All nonzero digits are significant
203.47 g
 Zeros occurring between significant digits are significant
56.06 g
 All final zeros past the decimal point are significant
73.00 g
 Zeros used as placeholders are NOT significant
0.09
The Atlantic-Pacific Rule
• If a decimal point is present in the measurement,
begin counting non-zero digits from the pacific side
• If a decimal point is absent in the measurement,
begin counting non-zero digits from the Atlantic side
0.0026701 - 5
significant digits
452000 - 3
significant digits
25.50 - 4 significant
digits
Calculating Derived Units
• Volume of a cube = L x W x H
– 2.56cm x 4.55cm x 2.56cm = 29.8 cm3 (3 sig figs)
• Area of a plot = L x W
– 12.5m x 25.55m= 319 cm3 (3 sig figs)
• Density of an object = M / V
– 23.50gr / 15.2mL = 1.55 g/mL (3 sig figs)
Learning Goals – Part Two
• Identify the 3 commonly used measurement
systems
• Identify two reasons why the English System may
not be preferred in the scientific world
• Understand metric unit relationships and convert
metric units.
• Identify the seven common base units in the SI
system
• Differentiate between qualitative and
quantitative observations and data
• Evaluate measurement data for precision and
accuracy
3 Measurement Systems In Use Today
1. English
2. Metric
3. SI
http://www.youtube.com/watch?v=3ffryZAd4Nw
NASA Measuring Failure
• The series of
measurement units that
most US residents are
taught and learn through
experience
• Developed over
thousands of years and
was influenced by many
different cultures
2 Good Reasons Why the Scientific World
does not prefer the English System?
•US
•Liberia
•Myanmar
(formerly
Burma)
1. It is used in very few nations throughout the world
2. The unit relationships appear random or are not well organized
Ex
12 in= 1 ft
3 ft = 1 yd
5280 ft = 1 mile
Metric System
• A highly organized system that
relies on factors of 10, base
units, and prefixes to define the
value of a measurement
Example: milli-
- meter
• Each unit is related through
some factor of ten and prefixes
change the value of the
measurement unit
Multiplying & Dividing by
• 3 common base units:
factors of 10
25.0 x 10 = 250.
– meter, liter and gram
25.0 / 10 = 2.5
SI – International System of
Accepted Base Units
• SI- Internationally
adopted use of a
standardized set of
units for measurement
• There are 7 base units
that have been
accepted to
standardize
international use
*In this system base units are the agreed units of measure in the International Community
Metric Prefixes
109 giga106 mega103 kilo101 deka100 Base Units
10-1 deci
10-2 centi
10-3 milli-
( liter, meter, gram)
10-6 micro10-9 nano-
10-12 pico
Fill in the blanks
•
•
•
•
•
1x10-2
1 centimeter = ___________
meter
milliliter
1 __________
= 1x10-3 liter
1x10-6
1 microgram = __________gram
kilovolt
1 __________
= 1x103 volts
-9
1x10
1 nanosecond = ________________ second
2 Useful Types of Measurements
Qualitative
•No “n” so NO
NUMBERS
•Any observation that
lacks numbers: color,
shape, odor, category
Qualitative Measurements
Advantages for their use:
Cheap, fast results, easy to
perform
http://www.youtube.com/watch?v=afddl33yq3s
Quantitative
•“n” is for NUMBER
•Any observation that
involves numbers:
counting, measuring,
calculating, etc.
Quantitative Measurements
Advantages:
Typically more accurate
Correctly Recording Measurements
A correctly recorded
measurement must
include
• A number
• unit of measure
• The correct number of
significant figures
(digits)
Precision
vs
Accuracy
Reliable Measurements Meet 2 Important
Conditions
• Accurate – how close to the “target”
or correct value – “correctness”
• Precise – how close is each
measurement to the other
measurements – “reproducibility”
Examining Precision and Accuracy
Uncertainty in Measurements
• Are digital measurements more certain or
accurate than analog measurements?
• Are digital measurements more reproducible
or precise than analog measurements?
Uncertainty in Measurements
• Measurements are uncertain for two reasons:
1. Measuring instruments are never completely
free of flaws
2. Measuring always involves some type of
estimation
Error Exists for All Measurements
Performed
• Measurement Error- All measurements
performed have error associated with them
because they are limited by the devices used
• The amount of error can be minimized when
we understand how exact ( many significant
figures are needed) a measurement needs to be
– “choose the right tools or devices”
2 Mathematical Methods for
Analyzing Measurement Accuracy
• 1) Error- The mathematical difference
between a measured value and an accepted
value. ( It might be a positive or negative
amount.) Error = Accepted - Measured
• 2) Percent Error Using a Formula
Analyzing Measurement Data for Accuracy and Precision
Batches of Campbell’s Chicken & Stars Soup are prepared in such a way that the accepted
value for sodium in one serving is 960 mg. Five local Bucks County schools measured
the amount of sodium found in one serving of this soup. Each school performed the same
analysis three times and the results are summarized in the table below.
School
Measurement
Trial 1
Measurement
Trial 2
Measurement
Trial 3
BCTHS
970 mg
985 mg
977 mg
Pennsbury
840 mg
845 mg
843 mg
Neshaminy
962 mg
821 mg
1040 mg
Bensalem
1575 mg
425 mg
955 mg
Bristol
1100 mg
450 mg
925 mg
Which school had the most accurate data? Explain why.
Which school had the most precise data? Explain why.
Calculate the percent error for Bensalem measurement trial 1.
Calculate the percent error for BCTHS measurement trial 3.