Download Measurement - TrimbleChemistry

Scientific Measurement
Units of Measurement
I
II
III
 August 20th – 2nd, 3rd, 6th Periods
 August 21st – 6th, 7th Periods
Number vs. Quantity
 Quantity - number + unit
UNITS MATTER!!
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 = CORRECT
PRECISE = CONSISTENT
A. Accuracy vs. Precision
B. Percent Error
 Indicates accuracy of a measurement
% error 
experimental  accepted
accepted
your value
given value
 100
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.
% error 
 2.94%
1.40 g/mL  1.36 g/mL
1.36 g/mL
 100
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
2.31 cm
C. Significant Figures
 Counting Sig Figs
 Digits from 1-9 are always significant
739
 Zeros between two other sig figs are always
significant 5085
 Zeros at the end of a number are significant
when a decimal is present
2.60
 Count all numbers EXCEPT:

Leading zeros -- 0.0025

Trailing zeros without
a decimal point -- 2,500
C. Significant Figures
Counting Sig Fig Examples
1. 23.50
2. 402
3. 5,280
4. 0.080
C. Significant Figures
 Calculating with Sig Figs
 Multiply/Divide - The # with the fewest
sig figs determines the # of sig figs in
the answer
(13.91g/cm3)(23.3cm3) =
C. Significant Figures
 Calculating with Sig Figs (con’t)
 Add/Subtract – Answer can have as
many # after the decimal as the # with
the least amount of # to the right of the
decimal
3.75 mL
+ 4.1 mL
7.85 mL
C. Significant Figures
 Calculating with Sig Figs (con’t)
 Exact Numbers do not limit the # of sig
figs in the answer
 Counting
 Exact
 “1”
numbers: 12 students
conversions: 1 m = 100 cm
in any conversion: 1 in = 2.54 cm
C. Significant Figures
Practice Problems
5. (15.30 g) ÷ (6.4 mL)
6. 18.9 g
- 0.84 g
 August 21st – 2nd, 3rd periods
 August 22nd- 5th, 6th, 7th periods
D. Scientific Notation
 A way to express any number as a
number between 1 and 10 (coefficient)
multiplied by 10 raised to
a
power (exponent)
 Mass
of one
carbonatoms
atom
Number
of carbon
the Hope diamond
in
460,000,000,000,000,000,000,000
0.00000000000000000000002 g
23
4.6 x 10
2 x 10-23 g
coefficient
exponent
D. Scientific Notation
65,000 kg  6.5 × 104 kg
 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 – all of them!
D. Scientific Notation
Practice Problems
7. 2,400,000 g
8. 0.00256 kg
9. 7.0  10-5 km
10. 6.2  104 mm
D. Scientific Notation
 Calculating with Sci. Notation
(5.44 × 107 g) ÷ (8.1 × 104 mol) =
Type on your calculator:
5.44
EXP
EE
7
÷
8.1
EXP
EE
4
EXE
ENTER
= 671.6049383 = 670 g/mol = 6.7 × 102 g/mol
D. Scientific Notation
Practice Problems
11. (4 x 102 cm) x (1 x 108cm)
12. (2.1 x 10-4kg) x (3.3 x 102 kg)
13. (6.25 x 102) ÷ (5.5 x 108)
14. (8.15 x 104) ÷ (4.39 x 101)
15. (6.02 x 1023) ÷ (1.201 x 101)
 August 26th- 2nd, 3rd, 5th, 6th, 7th
periods
CH. 3 - MEASUREMENT
Temperature
Conversions
A. Temperature
 Temperature
 measure of the average
KE of the particles in a
sample of matter
Kelvin  oC  273.15
9o
Fahrenheit 
C  32
5
5 o
Celsius  ( F  32)
9
A. Temperature
 Convert these temperatures:
1) 25oC = ______________K
2) -15oF = ______________ K
3) 315K = ______________ oC
4) 288K = ______________ oF
CH. 3 - MEASUREMENT
Dimensional Analysis
I
II
III
Conversion Factors
Problems
A. Problem-Solving Steps
1. Analyze
2. Plan
3. Compute
4. Evaluate
B. Dimensional Analysis
 Dimensional Analysis
 A tool often used in science for
converting units within a measurement
system
 Conversion Factor
 A numerical factor by which a quantity
expressed in one system of units may
be converted to another system
B. Dimensional Analysis
 The “Factor-Label” Method
 Units, or “labels” are canceled, or
“factored” out
g
cm 

g
3
cm
3
B. Dimensional Analysis
 Steps to solving problems:
1. Identify starting & ending units.
2. Line up conversion factors so units
cancel.
3. Multiply all top numbers & divide by
each bottom number.
4. Check units & answer.
C. Conversion Factors
Fractions in which the numerator and
denominator are EQUAL quantities
expressed in different units
Example:
Factors:
1 in. = 2.54 cm
1 in.
2.54 cm
and
2.54 cm
1 in.
How many minutes are in 2.5 hours?
Conversion factor
2.5 hr x 60 min
1 hr
1
cancel
= 150 min
By using dimensional analysis / factor-label method,
the UNITS ensure that you have the conversion right
side up, and the UNITS are calculated as well as the
numbers!
C. Conversion Factors
Learning Check:
Write conversion factors that
relate each of the following pairs
of units:
1. Liters and mL
2. Hours and minutes
3. Meters and kilometers
D. SI Prefix Conversions
1. Memorize the following chart. (next slide)
2. Find the conversion factor(s).
3. Insert the conversion factor(s) to get to the
correct units.
4. When converting to or from a base unit, there
will only be one step. To convert to or from any
other units, there will be two steps.
A. SI Prefix Conversions
move right
move left
Prefix
Symbol
Factor
tera-
T
1012
gigamegakilohectodekaBASE UNIT
decicentimillimicronanopico-
G
M
k
h
da
--d
c
m

n
p
109
106
103
102
101
100
10-1
10-2
10-3
10-6
10-9
10-12
D. SI Prefix Conversions
Tera-
1 T(base) = 1 000 000 000 000(base) = 1012 (base)
Giga-
1 G(base) = 1 000 000 000 (base) = 109 (base)
Mega-
1 M(base) = 1 000 000 (base) = 106 (base)
Kilo-
1 k(base) = 1 000 (base) = 103 (base)
Hecto-
1 h(base) = 100 (base) = 102 (base)
Deka-
1 da(base) = 101 (base)
Base
1 (base) = 1 (base)
Deci-
10 d(base) = 1(base)
Centi-
100 c(base) = 1 (base)
Milli-
1000 m (base) = 1(base)
Micro-
1 (base) = 1 000 000 µ = 10-6(base)
Nano-
1 (base) = 1 000 000 000 n = 10-9(base)
Pico-
1 (base) = 1 000 000 000 000 p = 10-12(base)
D. SI Prefix Conversions
a. cm to m
b. m to µm
c. ns to s
d. kg to g
D. SI Prefix Conversions
1) 20 cm =
______________ m
2) 0.032 L = ______________ mL
3) 45 m =
______________ m
D. SI Prefix Conversions
4) 805 Tb = ______________ b
Terabytes
bytes
D. SI Prefix Conversions
1) 400. g = ______________ kg
1) 57 Mm = ______________ nm
E. Dimensional Analysis Practice
 You have $7.25 in your pocket in
quarters. How many quarters do
you have?
7.25 dollars
1
X
4 quarters
1 dollar
E. Dimensional Analysis Practice
How many seconds are in 1.4
days?
1.4
24 hr 60
days
min
60 s
1
day
1
min
1 hr
= 12000 s
E. Dimensional Analysis Practice
 How many milliliters are in 1.00 quart of
milk?
E. Dimensional Analysis Practice
 You have 1.5 pounds of gold. Find its
volume in cm3 if the density of gold is
19.3 g/cm3.
E. Dimensional Analysis Practice
5) Your European hairdresser wants to cut
your hair 8.0 cm shorter. How many
inches will he be cutting off?
E. Dimensional Analysis Practice
6) Roswell football needs 550 cm for a 1st
down. How many yards is this?
E. Dimensional Analysis Practice
7) A piece of wire is 1.3 m long. How many
1.5-cm pieces can be cut from this wire?
E. Dimensional Analysis Practice
 How many liters of water would fill a
container that measures 75.0 in3?