Transcript Measurement

Chapter 1
Matter &
Measurement
Chemistry
is…
…the study of the
composition, structure,
and properties of matter
and the changes it
undergoes
C2H5OH + 3 O2  2 CO2 + 3 H2O + Energy
Reactants

Products
Matter
Anything that has mass and occupies
space
Mass
Atom
The smallest unit of an element that maintains
the properties of that element
Element
A pure substance made of only one kind of atom
Properties of
Matter
Extensive properties depend on the amount
of matter that is present.
Volume
Mass
Energy Content (think Calories!)
Intensive properties do not depend on the
amount of matter present.
Melting point
Boiling point
Density
Physical
Change
A change in a substance that does not involve a
change in the identity of the substance.
Example:
Phase Changes
Phase
Differences
Solid – definite volume and shape; particles packed
in fixed positions.
Liquid – definite volume but indefinite shape;
particles close together but not in fixed positions
Gas – neither definite volume nor definite shape;
particles are at great distances from one another
Plasma – high temperature, ionized phase of matter
as found on the sun.
Three Phases
Copper Phases - Solid
Copper Phases - Liquid
Copper Phases – Vapor
(gas)
Chemical Change
A change in which one or more substances are
converted into different substances.
Heat and light are
often evidence of
a chemical change.
Separation of a Mixture
The constituents of the mixture retain their
identity and may be separated by physical
means.
Separation of a Mixture
The components of dyes
such as ink may be
separated by paper
chromatography.
Filtration:
Separation of a Mixture
Distillation
Separation of a Compound
The Electrolysis of water
Compounds must be
separated by chemical
means.
With the application of
electricity, water can
be separated into its
elements
Reactant

Water

H2O

Products
Hydrogen + Oxygen
H2
+
O2
Measurement
Nature of Measurement
Measurement - quantitative observation
consisting of 2 parts
•
Part 1 - number
Part 2 - scale (unit)
•
Examples:
• 20 grams
• 6.63 x 10-34 Joule seconds
The Fundamental SI Units
(le Système International, SI)
SI Prefixes
Common to Chemistry
Prefix
Unit
Abbr.
Exponent
Kilo
Deci
Centi
Milli
Micro
k
d
c
m

103
10-1
10-2
10-3
10-6
Temperature Scales
The Thermometer
o Determine the
temperature by reading
the scale on the
thermometer at eye
level.
o Read the temperature
by using all certain
digits and one uncertain
digit.
o Certain digits are determined from the calibration
marks on the thermometer.
o The uncertain digit (the last digit of the reading) is
estimated.
o On most thermometers encountered in a general
chemistry lab, the tenths place is the uncertain digit.
Do not allow the tip to touch the
walls or the bottom of the flask.
If the thermometer bulb
touches the flask, the
temperature of the glass
will be measured instead of
the temperature of the
solution. Readings may be
incorrect, particularly if
the flask is on a hotplate
or in an ice bath.
Reading the Thermometer
Determine the readings as shown below on Celsius
thermometers:
8 _
7. _
4 C
_
3
0 C
_5
_ . _
Volume Instruments
Reading the Meniscus
Always read volume from
the bottom of the
meniscus. The meniscus
is the curved surface of
a liquid in a narrow
cylindrical container.
Try to avoid parallax errors.
Parallax errors arise when a meniscus or needle is
viewed from an angle rather than from straight-on
at eye level.
Incorrect: viewing the
meniscus
from an angle
Correct: Viewing the
meniscus
at eye level
Measuring Volume
 Determine the volume contained in a graduated
cylinder by reading the bottom of the meniscus at
eye level.
 Read the volume using all certain digits and one
uncertain digit.
 Certain digits are determined from
the calibration marks on the cylinder.
The uncertain digit (the last digit of
the reading) is estimated.
Use the graduations to find all
certain digits
There are two
unlabeled graduations
below the meniscus,
and each graduation
represents 1 mL, so
the certain digits of
the reading are… 52 mL.
Estimate the uncertain digit and
take a reading
The meniscus is about
eight tenths of the
way to the next
graduation, so the
final digit in the
reading is 0.8 mL .
The volume in the graduated cylinder is 52.8 mL.
10 mL Graduate
What is the volume of liquid in the graduate?
6
6_
_ . _
2 mL
Uncertainty in Measurement
•
A digit that must be estimated is
called uncertain. A measurement
always has some degree of
uncertainty.
Why Is there Uncertainty?
 Measurements are performed with instruments
 No instrument can read to an infinite number of
decimal places
Which of these balances has the greatest
uncertainty in measurement?
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
Significant Digits:
Atlantic/ Pacific Rule
• Atlantic • When the decimal is ABSENT, go to the
Atlantic side of the number, start
counting digits when you reach a nonzero number. Record
Practice
• 45,000 hrs
•
two
• 78,700 kilometers
•
three
• 3,000 liters
•
one
• Pacific - when the decimal is
PRESENT, go to the Pacific side
of the number, start counting
digits when you reach a nonzero number
Practice
• .009999 grams
• 4
• 560.03 mL
• 5
• 100.0 meters
• 4
• .00506
• none
Rules for Counting Significant
Figures - Details
•
Nonzero integers always
count as significant figures.
• 3456 has
• 4 sig figs.
Rules for Counting Significant
Figures - Details
• Zeros
•
- Captive zeros always count
as
significant figures.
• 16.07 has
• 4 sig figs.
More practice
•
•
•
•
•
56,000,000 seconds
33,000 candles
60900 milligrams
.899000 centimeters
.6700 meters
2
0
3
6
4
*
Sig Fig Practice #1
How many significant figures in each of the following?
1.0070 m 
5 sig figs
17.10 kg 
4 sig figs
100,890 L 
5 sig figs
3.29 x 103 s 
3 sig figs
0.0054 cm 
2 sig figs
3,200,000 
2 sig figs
Density – a derived measure
value is found through
mathematical computation
D=Mass/ Volume
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
.
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.
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.