BASIC CHEMISTRY
CHM 138
CHAPTER 1:
UNITS OF
MEASUREMENTS
Chemistry is the study of matter and the changes it
undergoes
Matter is anything that occupies space and has
mass.
A substance is a form of matter that has a definite
composition and distinct properties.
liquid nitrogen
gold ingots
silicon crystals
DIMENSIONS
 Defined as:
Any physical quantities that can be measured by
measuring devices.
 There are 2 types of dimension:
1.Basic dimension
o
o
The simplest and the most basic physical quantities
There are 7 basic dimensions:
- Length (L)
- mass (m)
- time (t)
- temperature (T)
- amount of substances (n)
- luminous intensity (I)
- electrical current
2. Derived dimensions
o The compound physical quantities that are obtained by
combining basic physical by multiplying / dividing the
basic dimensions.
Derived dimensions
Combination of Basic
dimensions
Area
Length x length
Volume
Length x length x length
Speed
Length / time
Force
(mass x length) / (time x time)
Density
Mass / (length x length x length)
Pressure
Mass / (time x time)
International System of Units (SI)
S.I system of units
Dimension
Symbol of
dimension
Name of unit
Symbol of unit
Definition of unit
Basic SI Units
length
L
meter
m
mass
m
kilogram
Kg
time
t
second
s
temperature
T
Kelvin, degree celcius
K, °C
Amount of substance
n
mole
mol
Derived SI Units
Energy
E
Joule
J / Nm
Kg.m2.s-2
Force
F
Newton
N
Kg.m.s-2
Power
P
watt
W /J/s
Kg.m2.s-3
Velocity
V
Meter per second
m.s-1
Acceleration
a
Meter per second squared
m.s-2
Pressure
P
Newton per meter squared,
Pascal
N.m-2
Pa
Density
ƿ
Kilogram per cubic meter
Kg.m-3
American Engineering system of units
Dimension
Symbol of
dimension
Name of unit
Symbol of unit
Basic SI Units
length
L
Feet
ft
mass
m
Pound mass
Ibm
force
F
Pound force
Ibf
time
t
Second
S
temperature
T
Degree Rankie,
Degree Fahrenheit
°R
°F
Amount of substance
n
mole
Ib mol
Derived SI Units
Energy
E
Foot pound force
Ft.Ibf
Force
F
Pound force
Ibf
Power
P
Horsepower
hp
Velocity
V
feet per second
ft.s-1
Acceleration
a
feet per second squared
ft.s-2
Pressure
P
Pound force per second
inch
Psi
Density
ƿ
Pound mass per cubic foot
Ibm.ft-3
Definition of unit
Quantity
Equivalent Values
Mass
1 kg = 1000 g = 0.001 metric ton = 2.20462 Ibm = 35.27392 oz
1 Ibm = 16 oz = 5 x 10-4 ton = 453.593 g = 0.453593 kg
Length
1 m = 100 cm = 1000 mm = 106 microns (µm) = 1010 angstroms (A)
= 39.37 in. = 3.2808 ft = 1.0936 yd = 0.0006214 mile
1 ft = 12 in. = 1/3 yd = 0.304 m = 30.48 cm
Volume
1 m3 = 1000 L = 106 cm3 = 106 mL
= 35.3145 ft3 = 220.83 imperial gallons = 264.17 gal
= 1056.68 qt
3
1 ft = 1728 in.3 = 7.4805 gal = 0.028317 m3 = 28.317 L
= 28,317 cm3
Force
1 N = 1 kg.m/s2 = 105 dynes = 105 g.cm/s2 = 0.22481 Ibf
1 Ibf = 32.174 Ibm.ft/s2 = 4.4482 N = 4.4482 x 105 dynes
Pressure
1 atm = 1.01325 x 105 N/m2 (Pa) = 101.325 kPa = 1.01325 bar
= 1.01325 x 106 dynes/cm2
= 760 mm Hg
= 14.696 Ibf/in.2 (psi) = 33.9 ft
= 29.921 in. Hg
Energy
1 J = 1 N.m = 107 ergs = 107 dyne.cm
= 2.778 x 10-7 kW.h = 0.23901 cal
= 0.7376 ft-Ibf = 9.486 x 10-4 Btu
power
1 W = 1 J/s = 0.23901 cal/s = 0.7376 ft.Ibf/s = 9.486 x 10-4 Btu/s
= 1.341 x 10-3 hp
1 year = 365 days
1 day = 24 hours
1 hour = 60 minutes
1 minute = 60 seconds
30 days = 1 month
1 year = 12 month
1 qt = 0.946 L
1 gal = 3.785 L
1 L = 33.81 fl oz
1 fl oz = 29.57 ml
1 L = 1.057 qt
1 in = 2.54 cm
1 m = 39.37 in
1 mile = 1.609 km
1 mile = 5280 feet
1 mile = 1760 yards
3 feet = 1 yard
12 inches = 1 feet
1 oz = 28.35 g
1 lb = 453.6 g
1 kg = 2.205 lb
1 g = 15.43 grains
MASS AND WEIGHT
Matter - anything that occupies space and has mass.
mass – measure of the quantity of matter
SI unit of mass is the kilogram (kg)
1 kg = 1000 g = 1 x 103 g
weight – force that gravity exerts on an object
weight = c x mass
A 1 kg bar will weigh
on earth, c = 1.0
1 kg on earth
on moon, c ~ 0.1
0.1 kg on moon
VOLUME
Volume – SI derived unit for volume is cubic meter (m3)
1 cm3 = (1 x 10-2 m)3 = 1 x 10-6 m3
1 dm3 = (1 x 10-1 m)3 = 1 x 10-3 m3
1 L = 1000 mL = 1000 cm3 = 1 dm3
1 mL = 1 cm3
DENSITY
Density – SI derived unit for density is kg/m3
1 g/cm3 = 1 g/mL = 1000 kg/m3
m
mass
d= V
density =
volume
EXAMPLE:
A piece of platinum metal with a density of 21.5 g/cm3
has a volume of 4.49 cm3. What is its mass?
m
d= V
m = d x V = 21.5 g/cm3 x 4.49 cm3 = 96.5 g
Ex. 1.1
Ex. 1.2
A Comparison of Temperature Scales
Three temperature scales:
i)
0F
– degrees Fahrenheit
ii)
0C
– degrees Celcius
iii) K - Kelvin
K = oC + 273.15
oF
=
oC
9 oF o
oF
x
C
+
32
5 oC
= (oF – 32oF) x
5 oC
9 oF
Example:
Convert 172.9 0F to degrees Celsius.
= 5 x (0F – 32)
9
0C = 5 x (172.9 – 32) = 78.3
9
0C
Scientific Notation
The number of atoms in 12 g of carbon:
602,200,000,000,000,000,000,000
6.022 x 1023
The mass of a single carbon atom in grams:
0.0000000000000000000000199
1.99 x 10-23
N x 10n
N is a number
between 1 and 10
n is a positive or
negative integer
568.762
0.00000772
move decimal left
move decimal right
n>0
n<0
568.762 = 5.68762 x 102
0.00000772 = 7.72 x 10-6
Addition or Subtraction
1. Write each quantity with the same exponent n
2. Combine N1 and N2
3. The exponent, n, remains the same
4.31 x 104 + 3.9 x 103 = 4.31 x 104 + 0.39 x 104
= 4.70 x 104
Multiplication
1. Multiply N1 and N2
2. Add exponents n1 and n2
(4.0 x 10-5) x (7.0 x 103) = ?
= (4.0 x 7.0) x (10-5+3)
= 28 x 10-2
m) x (b x 10n) = (axb) x 10m+n
(a
x
10
= 2.8 x 10-1
Division
1. Divide N1 and N2
2. Subtract exponents n1 and n2
8.5 x 104 ÷ 5.0 x 109 = ?
= (8.5 ÷ 5.0) x 104-9
m) ÷ (b x 10n) = (a ÷ b) x 10m-n
(a
x
10
= 1.7 x 10-5
Significant Figures
- The meaningful digits in a measured or calculated quantity.
RULES:
• Any digit that is not zero is significant
1.234 kg
4 significant figures
• Zeros between nonzero digits are significant
606 m
3 significant figures
• Zeros to the left of the first nonzero digit are not significant
0.08 L
1 significant figure
• If a number is greater than 1, then all zeros to the right of the
decimal point are significant
2.0 mg
2 significant figures
• If a number is less than 1, then only the zeros that are at
the end and in the middle of the number are significant
0.00420 g
3 significant figures
• Numbers that do not contain decimal points, zeros after
the last nonzero digit may or may not be significant.
400 cm
1or 2 or 3 significant figures
4 x 102
1 significant figures
4.0 x 102
2 significant figures
How many significant figures are in each of
the following measurements?
24 mL
2 significant figures
3001 g
4 significant figures
0.0320 m3
3 significant figures
6.4 x 104 molecules
2 significant figures
560 kg
2 significant figures
Significant Figures
Addition or Subtraction
The answer cannot have more digits to the right of the decimal
point than any of the original numbers.
89.332
+1.1
90.432
3.70
-2.9133
0.7867
one significant figure after decimal point
round off to 90.4
two significant figures after decimal point
round off to 0.79
Significant Figures
Multiplication or Division
The number of significant figures in the result is set by the original
number that has the smallest number of significant figures
4.51 x 3.6666 = 16.536366 = 16.5
3 sig figs
round to
3 sig figs
6.8 ÷ 112.04 = 0.0606926 = 0.061
2 sig figs
round to
2 sig figs
Significant Figures
Exact Numbers
Numbers from definitions or numbers of objects are considered
to have an infinite number of significant figures
The average of three measured lengths; 6.64, 6.68 and 6.70?
6.64 + 6.68 + 6.70
= 6.67333 = 6.67 = 7
3
Because 3 is an exact number
Dimensional Analysis Method of Solving Problems
1. Determine which unit conversion factor(s) are needed
2. Carry units through calculation
3. If all units cancel except for the desired unit(s), then the
problem was solved correctly.
given quantity x conversion factor = desired quantity
given unit x
desired unit
given unit
= desired unit
Dimensional Analysis Method of Solving Problems
How many mL are in 1.63 L?
Conversion Unit 1 L = 1000 mL
1000 mL
1.63 L x
= 1630 mL
1L
The speed of sound in air is about 343 m/s. What is this
speed in miles per hour?
conversion units
meters to miles
seconds to hours
1 mi = 1609 m
1 min = 60 s
1 mi
60 s
m
x
x
343
s 1609 m
1 min
1 hour = 60 min
60 min
mi
x
= 767
hour
1 hour