Transcript Measurement Power Point

Measurement
Alchemy
How do you picture a chemist?
What is chemistry?
 Chemistry is the study of all things and the changes
they can undergo.
 Chemistry is called a central science because it
overlaps so many sciences.
 Chemical – is any substance with a definite
composition.
Chemists use the scientific method as a
systematic approach to gather knowledge.
 Observation
 Question
 Hypothesis
 Experiment
 Conclusion
 All hypotheses must be testable in order to be a
valid hypothesis.
Types of Observations
 Qualitative: Describes something using the 5 senses
 Quantitative: Uses numbers in the description
 Quantity – something that has magnitude, size,
or amount.
 Unit – a quantity adopted as a standard of
measurement
Experiment
 Natural Law – Describes how nature behaves
 Theory – Explains why nature behaves the way it
does
 A theory and a hypothesis are both
explanations, but a theory is an explanation
formed after much experimentation.
Variables in a Experiment
 Independent Variable - You control
 Dependent Variable – Variable factor – what is being
tested
 Experimental Control – Factor that remains constant
for comparison
Factors in an Experiment
1.
2.
3.
Independent: most regular variable – goes on the X-axis
Dependent: what you are testing – goes on the Y-axis
Experimental Control: part of the experiment that stays
the same.
Dependent variable
“Y” axis
Independent variable
“X” axis
Measurement in Chemistry
Measurement is a key ingredient in ALL sciences,
especially chemistry.
• Scientific Notation
• Accuracy and Precision
• Significant Figures
• Measurement Devices
• Metric System
• Dimensional Analysis
Scientific Notation is a shorthand
way of expressing a number.
Consists of two factors:
 Coefficient - a number between 1 and 10 (only 1 digit to
the LEFT of the decimal point)
 Base - a power of 10  “power of 10” shows the
number of 10’s that are to be multiplied together
 Examples on the number line:
1x102
4x101
1x100
1x10-10
1x10-1
Small
Numbers
Negative
Numbers
Large
Numbers
1x10-10
1x10-1
0
1x102
4x101
1x100
Adding and Subtracting
(without calculator)
 Exponents must be the same
 If number gets bigger, exponent gets smaller
 If number gets smaller, exponent gets larger
(8 x 10-2) + (3 x 10-4) - (2 x 10-3)
(80 x 10-3) + (0.3 x 10-3) – (2 x 10-3) =
78.3 x 10-3 = 7.83 x 10-2
Multiplication
(without calculator)
 Multiply number and add exponents
(base 10 remains the same)
(6 x 10-6)(8 x 103) =
48 x 10-3  4.8 x 10-2
(6 x 10-3)2 =
36 x 10-6 = 3.6 x 10-5
Division
(without calculator)
 Divide number and subtract exponents
(base 10 remains the same)
(7.2 x 10-8)÷(8 x 10-5) =
0.9 x 10-3  9 x 10-4
Cube Root
 Make number a whole number, take
cube root of number, multiply exponent
by 1/3.
(2.7 x 10-8)1/3 =
(27 x 10-9)1/3 =
3 x 10-3
Square Root
 Make number a whole number, take
square root of number, multiply
exponent by ½.
(1.44 x 10-6)1/2 =
(144 x 10-8)1/2 =
12 x 10-4 = 1.2 x 10-3
1st Commandment of Chemistry: KNOW THY CALCULATOR!
Find the “EE” key – it may
be a 2nd function!
If you have a
graphing
calculator look
for the following
keys:
Find the (-) key.
Find the “Exp” or “x10x”
1st Law of Chemistry:
Know Thy Calculator!
Look at the
calculator that is
similar to
yours…
Find the “(-)” or the
“+/-” key.
Uncertainty in Measurement
 Measurements are uncertain because:
 1) Instruments are not free from error.
 2) Measuring involves some estimation.
 Precision –when the instrument gives you about the same results
under similar conditions. The smaller the increments of
measurement an instrument has, the more precise it can be.
 Accuracy – when the experimental value is close to the actual
value.
 % Error = experimental – accepted value x 100
accepted value
What is the goal for a game of darts?
Hitting the Bulls Eye!
Label the following data as accurate,
precise, neither, or both.
 1) 200g, 1g, 40g
 Neither
 2) 78g, 80g, 79g
 Precise
 3) 16g, 14g, 17g
 Accurate and Precise
How to use a graduated
cylinder
Read the
meniscus
How to use a graduated cylinder
36.4 mL
19.0 mL
6.25 mL
Length - Rulers
3
3.7
4
5
3.6
3
4
5
3.63
3
4
5
Temperature
21.8
21.68
How to read a triple beam balance
28.570 g
Ohaus Triple Beam Balance Tutorial
Reading A Triple Beam Balance Tutorial
How to read a triple beam balance
109.076 g
Ohaus Triple Beam Balance Tutorial
Reading A Triple Beam Balance Tutorial
Significant Figures and Digits
 A prescribed decimal that determines the amount of rounding
off to be done base on the precision of the experiment.
 ALWAYS ESTIMATE 1 DIGIT MORE THAN THE
INSTRUMENT MEASURES.
 Significant digits include measured digits and the estimated
digit.
 Exact Numbers – Do not involve estimation
 ex. 12 in = 1 ft
VI. Significant Digits
 Use Atlantic-Pacific Rule – imagine a US map
decimal
decimal
point
point
Pacific
Atlantic
1100
1100.
2 significant digits
4 significant digits
11.010000
8 significant digits
2 significant digits
0.025
0.00035000
1,000,100
Decimal
Present
Start
counting
with the 1st
nonzero
digit and
count all
the rest.
5 significant digits
5 significant digits
Decimal
Absent
Start
counting
with the 1st
nonzero
digit and
count all
the rest.
Significant Digits in Addition and Subtraction
 Add or subtract numbers
 Answer can only be as exact as the least exact number.
(Look at the decimal place)
 Ex. 4.1 cm + 0.07cm
 4.17 cm
 4.2 cm
Significant Digits and Multiplication and Division
 Multiply and Divide the numbers.
 Round answer to the same number of significant digits as
the number with the fewest significant digits.
 Ex. 7.079 cm / 0.535 cm
 13.2317757
 13.2
Atmospheric pressure is
measured with a
barometer. This is a
glass tube sealed at one
end and filled with Hg.
Types of Manometers
Open Manometers
Using a Manometer
a device used to measure pressure
 Reading a Manometer
 Barometer containing Hg
Temperature Conversions
Celsius and Kelvin
K
= °C + 273
 °C = K - 273
 Zero Point on Kelvin Scale – Absolute Zero
 0 K and -273 °C
 Kinetic energy is energy of motion. Temperature is a
measure of kinetic energy. Since the temperature at
absolute zero is a true zero, there is no particle motion
Therefore, nothing can exist at absolute zero.
TEMPERATURE SCALES

Measurements:
basic to all sciences & all are
comparisons to a standard
 English – still used in US
 Metric – devised in the late 1700’s in France
 SI – Le Système Internationale d’Unités
 Modern metric system (1960)
 Based on 7 base units
 Base units are modified by prefixes
SI Base Units
1.
Length
meter (m)
2.
Mass (SI standard unit)
kilogram (kg)
3.
Time
second (s)
4.
Temperature
Kelvin (K)
5.
Amount of a substance
mole (mol)
6.
Electric current
ampere (A)
7.
Luminous intensity
candela (cd)
The Meter
 The original standard for the meter was kept in a safe in
France.
 The meter stick is a replica of that standard.
 A meter is made up of 100 centimeters and 1000
millimeters.
 Lasers are now used to determine the standard for a meter.
The Gram
 Mass is the amount of
matter in an object.
 1 cm3 of water = 1 gram.
 The standard kilogram is
kept under lock and key in
Washington, DC and other
cities around the world.
Metric Conversion
Derived Units
 Area: 2-D
 LxW
(m2)
 Volume: 3-D
 Solid - L x W x H
(m3)
 Liquid or irregular shaped object - graduated
cylinder
(L or cm3)
 Density
 mass/volume
(kg/m3)
The Liter
=
 The liter is 1000 mL
 10cm x 10cm x 10cm
 1 liter = 1000 cm3 = 1 dm3
 1 milliliter = 1 cm3 = 1 cc = 20 drops
Prefix
Abbreviation
Meaning
megakilo-
M
k
1,000,000
1,000
hectodekaBASE UNIT
(g, m, L)
h
da
100
10
Scientific
Notation
1 x 106
1 x 103
1 x 102
1 x 101
--------------
1
100
decicentimilli-
d
c
m
0.1
0.01
0.001
1 x 10-1
1 x 10-2
1 x 10-3
micronano-

n
0.000 001
0.000 000 001
1 x 10-6
1 x 10-9
pico-
p
0.000 000 000 001
1 x 10-12
Length Relationships
Conversions between units
 Factor-label method or dimensional
analysis – based on using unit equalities
60 s = 1 min
60 s
OR
1 min
1 min
60 s
Example 1: 3.6 x 104 s = ? days
1 hr
3.6 x 104 s 1 min
60 s
1 day
60 min 24 hr
=
0.42 days = 4.2 x 10-1 days
3.6 x 104 s x 1 min
60 s
__________________
x
1 hr
__________________
60 min
x
1 day
=
24 hr
__________________
Example 2: 36 mm3 = ? cm3
36 mm3
1 cm3
3
=
0.036
cm
1000 mm3
36 mm3
1 cm 1 cm
1 cm
10 mm 10 mm 10 mm
Example 3: A room measures 12 feet by 15 feet.
Calculate the minimum number of square yards of
carpet needed to cover this area.
180 ft2
1 yd2
9 ft2
= 20
2
yd
A closer look at density
 Physical = A characteristic of a substance that does not
involve a chemical change
 Examples: texture, state of matter, density, hardness,
boiling point
 Density = The ratio of the mass of a substance to the
volume of the substance.

D = mass / volume
Density Column
Density
Which is more dense: Diet or Regular Soda?
Density of an Irregular solid:
1- Find the mass of the object
2- Find the volume if the
object by water
displacement!
 The characteristic plot for a Direct
Relationship is a straight line graph.
 Indirect Relationship
 The characteristic plot for an Inverse
Relationship is a curve of the type
illustrated here. As one of the
variables increases, the other
decreases. Note: It is not a straight line
sloping downward.
Use the following data to determine the
density of aluminum.
A. Determine the density of aluminum from the analysis of data
from 5 samples.
1)
2)
3)
4)
5)
54.0-g
14.0-g
41.0-g
27.0-g
19.0-g
sample
sample
sample
sample
sample
has
has
has
has
has
a
a
a
a
a
volume
volume
volume
volume
volume
of
of
of
of
of
20.0 mL
5.0 mL
15.0 mL
10.0 mL
7.0 mL
HINT: Graph the data with volume as the independent variable.
The slope of the line is the density.
Reminders:
1)
2)
3)
4)
Label both the x and y axis
Give your graph a descriptive title
Make a BEST FIT line/curve
Show work for slope on graph
Density Graph
Density of Aluminum
60
Mass (g)
50
y = 2.7134x
40
30
20
10
0
0
5
10
Volume (mL)
BACK
15
20
Energy Transfer
 Heat-energy that is transferred from one object to
another due to a difference in temperature. (symbol for
heat = q)
 Temperature = a measure of the average kinetic energy of
the particles in a substance. Temperature is an intensive
property, and heat is an extensive property.
 Thermochemistry – the study of heat changes in a
chemical reaction.
 Heat vs. Temperature
Calorimetry
 Calorimetry is the study of heat flow and
measurement.
 Calorimetry experiments determine the heats of
reactions by making accurate measurements of
temperature changes produced by a calorimeter.
Calorimeter
Calorimeter
 Heat Capacity – amount of heat needed to raise the
temperature of an object 1°C.
 Specific Heat – amount of heat needed to raise 1g of a
substance 1°C.
-Symbol for specific heat is C.
Heat and Temperature
 Formula for heat absorbed for released:
q = C x m x ∆T
 Remember: Specific Heat of Water =
4.184 J/g· °C