Transcript Law v. Theory - Granbury ISD

Chemistry
The Importance in
Measurement
What type of Measurement are
made in Chemistry?
1. Qualitative Measurements
• Descriptive, non-numerical form
• Color, shape, size, feelings, texture
Example:
The basketball is round and brown.
2. Quantitative Measurements
• Definite form with numbers AND units
• Mass, volume, temperature, etc.
Example:
The basketball has a diameter of 31 cm
and a pressure of 12 lbs/in2.
Scientific Notation
In science, we deal with some very
LARGE numbers:
1 mole = 602000000000000000000000
In science, we deal with some very
SMALL numbers:
Mass of an electron =
0.000000000000000000000000000000091 kg
Imagine the difficulty of calculating
the mass of 1 mole of electrons!
0.000000000000000000000000000000091 kg
x 602000000000000000000000
???????????????????????????????????
Scientific Notation:
A method of representing very large or
very small numbers in the form:
M x 10n
 M is a number between 1 and 10
 n is an integer
# of times to move the decimal
If n is negative, the number is really
small
If n is positive, the number is really
large.
.
2 500 000 000
9 8 7 6 5 4 3 2 1
Step #1: Insert an understood decimal point
Step #2: Decide where the decimal must end
up so that one number is to its left
Step #3: Count how many places you bounce
the decimal point
Step #4: Re-write in the form M x 10n
2.5 x
9
10
The exponent is the
number of places we
moved the decimal.
Since it was a large
number, the
exponent is positive.
0.0000579
1 2 3 4 5
Step #2: Decide where the decimal must end
up so that one number is to its left
Step #3: Count how many places you bounce
the decimal point
Step #4: Re-write in the form M x 10n
5.79 x
-5
10
The exponent is negative
because the number we
started with was less
than 1.
PERFORMING
CALCULATIONS
IN SCIENTIFIC
NOTATION
ADDITION AND SUBTRACTION
4 x 106 IF the exponents are
6
+ 3 x 10 the same:
7 x 106 1. add or subtract
the numbers in front
2. bring the
exponent down
unchanged.
106
6
10
4 x
- 3 x
6
1 x 10
The same holds true
for subtraction in
scientific notation.
106
4 x
+ 3 x 105
If the exponents are
NOT the same, we
must move a decimal
to make them the
same.
6
5
xx 10
10
40.0
4.00
5
+ 3.00 x 10
43.00 x
= 4.300 x
Student A
To avoid this
NO!
problem, move
 Is this good
5
10 the decimal on
scientific
the smaller
6
notation?
10 number!
6
10
4.00 x
6
5
.30 x 10
+ 3.00
4.30 x
6
10
Student B
YES!
 Is this good
scientific
notation?
A Problem for you…
-6
10
2.37 x
-4
+ 3.48 x 10
Solution…
-6
-4
002.37
2.37 x 10
0.0237
x 10
-4
+ 3.48 x 10
-4
3.5037 x 10
PERFORMING
CALCULATIONS
IN SCIENTIFIC
NOTATION
MULTIPLICATION AND
DIVISION
4 x 106 IF the problem is
6
x 3 x 10 multiplication:
12 x 1012 1. Multiply the
numbers as usual
2. add the exponent.
24 x 109 IF the problem is
6
3 x 10 division:
8 x 103
1. Divide the
numbers as usual
2. subtract the
exponents:
numerator - denominator
Calculate the following answer:
0.000 000 000 000 000 000 000 000 000 000 91 kg
______
x 602 000 000 000 000 000 000 000
???????????????????????????????????
9.1 x 10-31
x 6.02 x 1023
54.782 x 10-8
5.4782 x 10-7 kg
Practice Problems #1
1.
5.7 x 106
2.
3.8 x 105 -
3.
1.35 x 107 +
+
3 x 105
2.1 x 106
8 x 105
4. 8.52 x 10-9 + 2.16 x 10-9
Practice Problems #2
5.
7 x 106 / 2 x 104
6.
5 x 108 x 5 x 103
7.
5 x 103 /
2 x 103
8. 2 x 107 x
4 x 10-9
Precision and Accuracy
Accuracy refers to the agreement of a particular
value with the true value.
Precision refers to the degree of agreement
among several measurements made in the same
manner.
Neither
accurate nor
precise
Precise but not
accurate
Precise AND
accurate
Percent Error
Accepted Value – Correct value based on reliable
references.
Example: Boiling Point of water is 100°C
Experimental Value – Value measure in lab.
Example: Boiling Point measured in lab reads 99.1°C
Percent | experimental value – accepted value | x 100
Error =
accepted value
|99.1 – 100| x 100
100
0.9 x 100 = 0.9% error
100
Errors less than 5-10% is acceptable!
International System of
Units (SI)
The Fundamental SI Units
(le Système International, SI)
Quantity
SI Base Unit
Symbol
Length
meter
m
Volume
cubic meter
m3
kilogram
km
grams / cubic
centimeter
g/cm3
Temperature
kelvin
K
Time
second
s
Pressure
pascal
Pa
atmosphere (atm)
Energy
joule
J
calorie (cal)
Amt of Subs.
mole
mol
Mass
Density
Other Symbols
liter (L)
grams / milliliter (g/mL)
degree Celcius (°C)
Prefixes in Measurements
Factor
Scientific
Notation
Prefix
Symbol
mega-
M
1 000 000
106
kilo-
k
1 000
103
deci-
d
1 / 10
10-1
centi-
c
1 / 100
10-2
milli-
m
1 / 1000
10-3
micro-
μ
1 / 1 000 000
10-6
nano-
n
1 / 1 000 000 000
10-9
pico-
p
1 / 1 000 000 000 000
10-12
Units of Length
Unit
Symbol
Relationship
Example
Kilometer
km
1 km = 103 m
Meter
m
base unit
Height of door knob
Decimeter
dm
101 dm = 1 m
Diameter of orange
Centimeter
cm
102 cm = 1 m
Width of button
Millimeter
mm
103 mm = 1 m
Thickness of dime
Micrometer
μm
106 μm = 1 m
Diameter of a bacteria
Nanometer
nm
109 nm = 1 m
Thickness of an RNA
Length of 5 city blocks
Units of Volume
Unit
Symbol
Relationship
L
base unit
Milliter
mL
103 mL = 1 L
20 drops of water
Cubic
Centimeter
cm3
1 cm3 = 1 mL
cube of sugar
Microliter
μL
106 μL = 1 L
crystal of table salt
Liter
Example
Quart of Milk
Units of Mass
Unit
Symbol
Relationship
Example
Kilogram
kg
base unit
1 kg = 103 g
small textbook
Gram
g
1 g = 10-3 kg
dollar bill
Milligram
mg
103 mg = 1 g
ten grains of salt
Microgram
μg
106 μg = 1 g
particle of baking
powder