Download International System of Units

International System of
Units
 Units provide a scale on which to
represent the results of a measurement
Measurements of Length
 Length
- Fundamental unit is the meter
1 meter = 39.37 inches
Measurements of Volume
 Volume
- amount of 3-D space occupies by a
substance
- fundamental unit is meter3 (m3)
1 cm3 = 1 ml
Items for measuring
volume
 Graduated cylinder- useful for dispensing
approximate volumes
 Buret- must be used when accuracy is
important
 Volumetric flask- contains a specified
volume of liquid
Measuring Mass
- Weight- mass times gravity
- Mass- the amount of matter in an object
- quantity of matter in an object
- fundamental unit is the kilogram
Measuring Density
Density = mass/ volume
Derived unit- a unit obtained from more than one base
unit.
Density- is a characteristic property that depends only on
the composition of a substance, not on the size of the
sample.
Pure substances have specific densities.
The density of a substance generally decreases as its
temperature increases. Water is an important
exception
Density Problems
1. What is the density of a block of marble that
occupies 310cm3 and has a mass of 853g?
2. Diamond has a density of 3.26g/cm3. What is
the mass of a diamond that has a volume of
0.350cm3?
3. What is the volume of a sample of liquid
mercury that has a mass of 76.2g, given that
the density of mercury is 13.6g/ml?
Measuring Specific
Gravity
Specific Gravity- a comparison of the
density of a reference substance. Water
is a common reference substance.
- Can be determined with a hydrometer
Specific Gravity = density of substance/
density of water
- Has no units
Measuring Temperature
Temperature- is related to the energy and
motion of particles
Temperature scales
Celsius scale- based on the freezing and
boiling points of water.
a. freezing point = 0 C
b. boiling point = 100 C
Kelvin scale- The zero point on the Kelvin
scale is absolute zero. The theoretical
point at which all motion stops. One
degree Kelvin equals one degree celsius
K= C + 273
C= K - 273
Measuring Temperature
Practice Problems
1. Normal human body temperature is 37
C. What is your temperature in Kelvin?
2. The boiling point of the element Argon
is 87 K. What is the boiling point of
argon in C?
The Importance of
measurement
Scientific Notation
Scientific notation
36,000 is 3.6 x 104
The exponent indicates how many times
the coefficient 3.6 must be multiplied by
10 to equal the number 36,000.
Large numbers have positive exponents
Small numbers (less than one) have
negative exponents.
0.0081 is 8.1 x 10-3, the exponent -3
indicates that the coefficient 8.1 must be
divided by 10 three times to equal 0.0081
Multiplication and Division
To multiply numbers written in scientific
notation, multiply the coefficients and add
the exponents
(3.0 x 104) x (2.0 x 102)= 6.0 x 106
To divide numbers written in scientific
notation, first divide the coefficient, then
subtract the exponent in the dominator
from the exponent in the numerator
3.0 x 104 / 2.0 x 102 = 1.5 x 102
Sample Problems
Write each measurement in scientific
notation
a. 222 meters
2.22 x 102 meters
b. 728500 meters
7.285 x 105 meters
c. 0.00054 meters
5.4 x 10-4 meters
Multiplication and Division
a. (3.0 x 105) x (2.6 x 103)=
7.8 x 108
b. (2.8 x 103) / (1.4 x 10-2)=
2.0 x 105
Conversion Factors
Conversion factor- a ration of eqvivalent
measurements, such as 100cm / 1m
The measurement in the numerator is
equivalent to the measurement in the
denominator.
Conversion factors are exact quantities.
Therefore, they have an unlimited
number of significant figures.