Transcript Measurement SI AandP

MEASUREMENT
Units of Measurement
Types of Data
Data refers to
information
Qualitative Data
Describes something
Texture, Color, etc
Quantitative Data
Measures Something
Length, Mass, Time,
etc
Determine if each of the following
is a qualitative or quantitative
measurement.
A.The sandwich has ham in it.
B.There are four eggs in the carton.
C.I used 230 grams of NaOH.
D.I added water to the solution.
Measurement
A quantity with both a NUMBER and a UNIT
Provides a reference point
NO NAKED NUMBERS!
Number vs. Quantity
Quantity = number + unit
Measurements
Accuracy
How close a measurement comes to the
accepted answer
Precision
How close a series of measurements are to
each other.
How specific an measurement is
10 vs. 10.01 vs. 10.007
Let’s use a golf analogy
Accurate? No
Precise? Yes
Accurate? Yes
Precise? Yes
Precise?
No
Accurate? No
Accurate? Yes
Precise? We can’t say!
Accurate? Precise?
Accurate? Precise?
Accurate? Precise?
Error
Accepted value – The right answer
• Based on reliable references
• Also called Theoretical Yield
Experimental Value- what you get in lab
• Also called Actual Yield
Measurements
Determining Error
How far your measurement is from the accepted
value.
Error  Experiment al Value  Accepted Value
Percent Error
Percent Error =
error
accepted value
100%
International System of
Measurements
Measurement
SI Base Unit
Symbol
Length
Meter
m
Mass
Kilogram
kg
Temperature
Kelvin
K
Time
Second
s
Amount
Mole
mol
Light Intensity
Candela
cd
Electric Current
Ampere
A
Prefix
Symbol
megaM
kilok
BASE UNIT
--decid
centic
millim
micro
nanon
picop
Factor
6
10
3
10
0
10
-1
10
-2
10
-3
10
-6
10
-9
10
-12
10
Significant Figures or Digits
Significant Figures (sig figs) are all digits which
show where an actual measurement is made;
the more sig figs, the better the measurement:
0.5 m (1 sig fig)
0.50 m (2 sig figs)
0.500 m (3 sig figs)
0.500 m was measured with a more accurate
ruler
Counting Sig Figs
Which digits are significant?
1. All non-zeroes are significant
2. A final zero after a decimal point is
significant
3. All zeroes between sig figs are significant
4. Zeroes that are place holders are not
significant and do not go into scientific
notation
How many sig figs in the
following measurements?
1.
2.
3.
4.
5.
6.
7.
8.
770 mL
0.0700 mL
7070 mL
0.007 mL
7.00 x 103 mL
7000 mL
70.070 mL
77.0 mL
1.
2.
3.
4.
5.
6.
7.
8.
2
3
3
1
3
1
5
3
Math with Sig Figs
Addition & Subtraction
The answer must be rounded to the same
number of decimal places as the
measurement with the fewest decimal
places (worst measurement).
527.38 m
+ 21.2 m
548.58 m  548.6 m
Math with Sig Figs
Multiplication & Division
The answer must be rounded to the same
number of sig figs as the measurement with
the fewest sig figs (worst measurement).
527.38 m (5)
x 21.2 m (3)
11180.456 m2  11200 m2 (3)
Scientific Rounding Rules
1. If the digit to be rounded is followed by
0,1,2,3, or 4 – do not round the digit /
leave digit alone
2. If the digit to be rounded is followed by
6,7,8, or 9 – round up the digit
3. If the digit to be rounded is followed by a
5 with any digits of value anywhere
behind the 5 – round up the digit
4. If the digit to be rounded is followed by
only a 5 or a 5 with no numbers of value
behind the 5 – odd digits round up and
even digits are left alone
Round the following
measurements to 2 sig figs:
1.
2.
3.
4.
5.
6.
32980 g
0.07810 m
355 mL
345 mL
o
798 C
24
5.92 x 10
atoms
7. 1450.01 km
1.
2.
3.
4.
5.
6.
7.
33000 g
0.078 m
360 mL
340 mL
2
o
8.0 x 10 C
24
5.9 x 10 atoms
1500 km