Inorganic chemistry
 Measurement in Scientific
 General Features of SI Units.
 Some Important SI Units in
Assistance Lecturer Amjad Ahmed Jumaa
 General Chemistry:
Chemistry: A science that deals with the composition, structure, and
properties of substances and with the transformations that they undergo.
 Measurement in Scientific study:
Measurement has a history characterized by the search for exact,
invariable standards.
 General Features of SI Units:
 For example, the derived unit for speed, meters per second (m/s), is the
base unit for length (m) divided by the base unit for time (s).
SI Base Units.
 Common Decimal Prefixes Used with Si Units.
 Some Important SI Units in Chemistry:
Let’s discuss some of the SI units length, volume, mass, density,
temperature, and time.
 Length:
 The SI base unit of length is the meter (m).
 The standard meter is defined as the distance light
travels in a vacuum in 1/299,792,458 second.
 Biological cells are often measured in micrometers
(1µm = 10-6 m).
 On the atomic-size scale, nanometers and
picometers are used (1 nm = 10-9 m; 1 pm = 10 -12m).
 Many proteins have diameters of around 2 nm;
atomic diameters are around 200 pm (0.2 nm). An
older unit still in use is the angstrom (1 Å= 10-10m =
0.1 nm = 100 pm).
 Volume:
 Any sample of matter has a certain volume (V), the amount
of space that the sample occupies.
 The SI unit of volume is the cubic meter (m3). In chemistry,
the most important volume units are non-SI units, the liter
(L) and the milliliter (mL) (note the uppercase L).
 A liter is slightly larger than a quart (qt) (1 L= 1.057 qt; 1 qt =
946.4 mL).
 Physicians and other medical practitioners measure body
fluids in cubic decimeters (dm3), which is equivalent to
1 L= 1 dm3= 10-3 m3
 As the prefix milli-indicates, 1 mL is 1/1000 of a liter, and it is
equal to exactly 1 cubic centimeter (cm3):
1 mL= 1 cm3 = 10-3 dm3 =10-3 L= 10-6 m3
 Converting Units of Volume:
The volume of an irregularly shaped solid can be
determined from the volume of water it displaces. A
graduated cylinder contains 19.9 mL of water. When a
small piece of galena, an ore of lead, is added, it sinks
and the volume increases to 24.5 mL. What is the volume
of the piece of galena in cm 3and in L?
We have to find the volume of the galena from the change in
volume of the cylinder contents. The volume of galena in mL
is the difference in the known volumes before (19.9 mL) and
after (24.5 mL) adding it. The units mL and cm3 represent
identical volumes, so the volume of the galena in mL equals
the volume in cm3. We construct a conversion factor to
convert the volume from (mL to L). The calculation steps are
shown in the roadmap on the next page.
 Mass:
The mass of an object refers to the quantity of matter it
The SI unit of mass is the kilogram (kg), the only base
unit whose standard is a physical object—a platinumiridium cylinder kept in France. It is also the only base
unit whose name has a prefix. (In contrast to the practice
with other base units, however, we attach prefixes to the
word “gram,” rather than to the word “kilogram”; thus,
10 -3 grams is 1 milligram, not 1 microkilogram.).
Its weight, on the other hand, depends on its mass and
the strength of the local gravitational field pulling on it.
 Converting Units of Mass:
International computer communications are often carried by optical fibers in
cables laid along the ocean floor. If one strand of optical fiber weighs (1.19
x10-3 lb/m), what is the mass (in kg) of a cable made of six strands of optical
fiber, each long enough to link New York and Paris (8.84 x10 3 km)?
We have to find the mass of cable (in kg) from the given mass/length of fiber
(1.19x10 -3lb/m), number of fibers/cable (6 fibers/cable), and the length (8.84x
10 3 km, distance from New York to Paris). One way to do this (as shown in
the roadmap) is to first find the mass of one fiber and then find the mass of
cable. We convert the length of one fiber from km to m and then find its
mass (in lb) by using the lb/m factor. The cable mass is six times the fiber
mass, and finally we convert lb to kg.
Converting the fiber length from km to m:
 Calculating Density from Mass and Length:
Lithium is a soft, gray solid that has the lowest density of any metal. It is an essential
component of some advanced batteries, such as the one in your laptop. If a small
rectangular slab of lithium weighs 1.49 X 10 3 mg and has sides that measure (20.9
mm) by (11.1 mm) by (11.9 mm), what is the density of lithium in g/cm 3?
To find the density in (g/cm3), we need the mass of lithium in (g) and the volume in
(cm3). The mass is given in mg (1.49 x 103 mg), so we convert (mg) to (g). Volume data
are not given, but we can convert the given side lengths (20.9 mm, 11.1 mm, 11.9
mm), from (mm to cm), and then multiply them to find the volume in cm 3. Finally,
we divide mass by volume to get density. The steps are shown in the roadmap.
Converting the mass from (mg to g):
 Temperature:
There is a common misunderstanding about heat and temperature.
Temperature (T) is a measure of how hot or cold a substance is relative to
another substance. Heat is the energy that flows between objects that are at
different temperatures.
We can convert between the Celsius and Kelvin scales by remembering the
difference in zero points: since
0°C = 273.15K:
T(in K ) = T (in 0°C ) + 273.15
T(in 0°C) = T(in K ) -273.15
 The Fahrenheit scale differs from the other scales in its zero point and
in the size of its unit. Water freezes at (32°F) and boils at (212°F).
Therefore, 180 Fahrenheit degrees (212°F- 32°F) represents the same
temperature change as (100 Celsius degrees (or 100 kelvins). Because
100 Celsius degrees equal 180 Fahrenheit degrees,
1 Celsius degree = 180/100 Fahrenheit degrees = 9/5 Fahrenheit degrees.
 To convert a temperature in °C to °F, first change the degree size and
then adjust the zero point:
T (in °F) = 9/5T (in °C) + 32
 To convert a temperature in °F to °C, do the two steps in the opposite
order; that is, first adjust the zero point and then change the degree size.
In other words, for T (in °C):
T(in °C)= [T(in °F)- 32]5/9
 (The only temperature with the same numerical value in the Celsius and
Fahrenheit scales is -40°; that is, -40°F = -40°C.)
 Converting Units of Temperature
Problem: A child has a body temperature of 38.7°C.
(a) If normal body temperature is 98.6°F, does the child have a fever?
(b) What is the child’s temperature in kelvins?
(a) To find out if the child has a fever, we convert from °C to °F and see
whether 38.7°C is higher than 98.6°F.
(b) Convert the temperature in °C to K.
Solution (a) Converting the temperature from °C to °F:
T (in °F) = 9/5T (in °C) +32 = 9/5(38.7°C) +32= 101.7 °F
(b) Converting the temperature from °C to K:
T (in K) =T (in °C) +273.15 =38.7°C +273.15 = 311.85

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